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Real-Time Event Reconstruction and Analysis in CBM and STAR
Experiments
To cite this article: Ivan Kisel and for CBM and STAR Collaborations 2020 J. Phys.: Conf. Ser. 1602 012006

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Real-Time Event Reconstruction and Analysis in CBM and STAR Experiments - IOPscience
36th Winter Workshop on Nuclear Dynamics                                                                        IOP Publishing
Journal of Physics: Conference Series                         1602 (2020) 012006          doi:10.1088/1742-6596/1602/1/012006

Real-Time Event Reconstruction and Analysis
in CBM and STAR Experiments
                      Ivan Kisel
                      (for CBM and STAR Collaborations)

                      1
                        Goethe-University Frankfurt, Theodor-W.-Adorno-Platz 1, 60323 Frankfurt am Main,
                      Germany
                      2
                        FIAS Frankfurt Institute for Advanced Studies, Ruth-Moufang-Str. 1, 60438 Frankfurt am
                      Main, Germany
                      3
                        Helmholtz Research Academy Hesse for FAIR, Max-von-Laue-Str. 12, 60438 Frankfurt am
                      Main, Germany
                      4
                        GSI Helmholtz Centre for Heavy Ion Research, Planckstr. 1, 64291 Darmstadt, Germany
                      E-mail: I.Kisel@compeng.uni-frankfurt.de

                      Abstract. Within the FAIR Phase 0 program, the algorithms of the FLES (First-Level Event
                      Selection) package developed for the CBM experiment (FAIR/GSI, Germany) are adapted for
                      the STAR experiment (BNL, USA). Use of the same algorithms creates a bridge between online
                      and offline, which makes it possible to combine online and offline resources for data processing.
                      In this way, an express data production chain was created on the basis of the STAR HLT farm,
                      that extends the functionality of HLT in real time up to the analysis of physics. It is important,
                      that the express analysis chain does not interfere with the standard analysis chain. A particular
                      advantage of express analysis is that it allows calibration, production and analysis of the data
                      to begin immediately after they are collected. Therefore, the use of express analysis is beneficial
                      for BES II data production and helps to speed up scientific discovery by helping to obtain
                      results within one year after the end of data acquisition. The specific features of express data
                      production are presented and discussed as well as the results of online production and analysis,
                      such as real-time reconstruction of short-lived particles in the BES-II STAR environment.

1. Introduction
Within the framework of the Facility for Antiproton and Ion Research (FAIR) project, a large
international centre is being constructed to study the structure and fundamental properties of
matter. It will be a new generation accelerator complex that will provide unique opportunities
for detailed investigations in the most interesting areas of modern science: nuclear, hadron and
particle physics, atomic and anti-matter physics, high density plasma physics, and applications
in condensed matter physics, biology and bio-medical sciences [1].
   In the Compressed Baryonic Matter (CBM) [2] experiment with heavy ions, the highest
baryon densities will be created, and the properties of super-dense nuclear matter will be
investigated in various extreme states that are similar to, for example, the conditions of matter
in the center of neutron stars, where matter is at the final stage of evolution before transition to
the black hole. The CBM experiment will thus complement the experimental heavy-ion program

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Real-Time Event Reconstruction and Analysis in CBM and STAR Experiments - IOPscience
36th Winter Workshop on Nuclear Dynamics                                                                                                                                                     IOP Publishing
                                   Journal of Physics: Conference Series                                                                                   1602 (2020) 012006                             doi:10.1088/1742-6596/1602/1/012006

                                    at the LHC accelerator complex at CERN where the properties of the hot matter similar to that
                                    after the Big Bang are investigated.
                                       The scientific program of the CBM experiment includes:
                                             •   explore properties of super-dense nuclear matter;
                                             •   search for in-medium modifications of hadrons;
                                             •   search for the transition from dense hadronic matter to quark-gluon matter;
                                             •   search for the critical endpoint in the phase diagram of strongly interacting matter;
                                             •   investigate the structure of neutron stars and the dynamics of core-collapse supernovae.
                                       The experiment will measure rare and penetrating probes such as dilepton pairs from light
                                    vector mesons and charmonium, open charm, multistrange hyperons, together with collective
                                                  KF
                                    hadron flow and     Particle:
                                                    fluctuations     Reconstruction
                                                                 in heavy-ion                  short-lived
                                                                              collisions at rates                 Particles
                                                                                                  up to 107 collisions per second.

                                                                                                                                                                                                    Concept:
                                                                                                π+
                                                                                                                                                                                              • Mother and daughter particles have the same state
                                                                                                                                                                                                 vector and are treated in the same way
                                                                                                                                                                                              • Reconstruction of decay chains
                                                                                                                          Κ+                                                        Figure • 1.KalmanAFiltersimulated
                                                                                                                                                                                                               (KF) based central Au-Au
                                                                                                                                                                                    collision •atGeometry
                                                                                                                                                                                                  25 AGeV        energy with about 1000
                                                                                                                                                                                                           independent
                                                                                                                                                                                              • Vectorizedin the CBM experiment.
                                                                                                                                                                                    charged particles
                                                                                                                                                                                              • Uncomplicated usage
                                                                                                                                         p
                                                                                                                                                                                                    Functionality:
                                                                        Λ                                         • Construction of short-lived particles
                                                 Ω+         Concept of KF Particle in CBM                         • Addition and subtraction of particles
                                                                                                                  • Transport
                                              1. KFParticle    class   describes
                                                                          collision at 25particles  by:           • Calculation of an angle between particles
  3        KFParticle: Reconstruction of Vertices      and   Decayed
                                                           Simulated AuAu
                                                                                   Particles
                                                                                          AGeV

                        π+                                      r = { x, y, z, px, py, pz, E }                    • Calculation of distances and deviations
                         CBM   is characterized           by Position,
                                                               highdirection,collision
                                                                                     2
                                                                                       s2 C     C rates,  C large
                                                                                                               3
                                                                                                                  •amount      ofonproduced
                                                                                                                     Constraints                  particles,
                                                                                                                                    mass, production             non-length
                                                                                                                                                       point and decay
                                             Λ̅ KΩ̅
                                                                                                    C   C    C
                           +          +                                              6 x
                                                                                                                                                     xy      xz     xpx     xpy      xpz     xE
                                                                                              2                7
                                             State vector   State vector            momentum
                                                                                     6C
                                                                                     6      s y C   C   C C  C 7
                                                                                                               7                              xy             yz     ypx     ypy      ypz     yE

                    homogeneous
                      π+        Κ + magnetic       fields
                                                (r,C)         and       and energy6
                                                                         a     very  6C     complex
                                                                                            C   sz2 C
                                                                C =  = 66C C C sp2 C C C 77
                                                                                     6
                                                                                                        C
                                                                                                          detector
                                                                                                          C
                                                                                                               7
                                                                                                             C 7
                                                                                                               7  • system.
                                                                                                                     KF Particle Event
                                                                                                                                 Finder  reconstruction
                                                                                                                                              xz     yz
                                                                                                                                                                is the
                                                                                                                                                                    zpx     zpy      zpz     zE

                                                 p̅ π+and time consuming task of the data analysis in modern high-energy physics
                                                                                                                                              xpx    ypx    zpx       x     px py    px pz   px E
                                                                                     6                         7
                                                                                                                                                                           sp2y Cpy pz Cpy E 7
                                    most complicated                                                       r = { x, y, z, px, py, pz,66CExp} Cyp
                                                                                                                                         6C
                                                                                                                                                y      y   Czpy Cpx py
                                                                                                                                         4 xpz Cypz Czpz Cpx pz
                                                                                                                                                                                             7
                                                                                                                                                                           Cpy pz sp2z Cpy E 7
                                                                                                                                                                                             5
                                                              Covariance matrix
                              experiments. Κ+        Itp is a key part of success in the CBM experiment                             Reconstruction
                                                                                                                                               with of
                                                                                                                                             CxE
                                                                                                                                                      updecays
                                                                                                                                                    CyE         with neutral
                                                                                                                                                          to thousand
                                                                                                                                                           CzE    C px E     daughter
                                                                                                                                                                           Cpy E Cpz E sE2
                                                                                                                                                                         particles
                                                                Concept:                                                                 by the missing mass method:
                                                                 2. Covariance        matrix   contains      essential   information
                              per central collision (Fig. 1). An additional complication in CBM is its continuous data stream
                                                                                                 • Mother and daughter particles have the same state
                                KFParticle Lambda(P,   Pi);                      // construct
                                                                    about tracking               anti Lambda
                                                                                        and detector       performance.
                        Λ represented
                                                  p
                                                   in form of3. time
                                Lambda.SetMassConstraint(1.1157);   The method slices.
                                                                                  // improve This
                                                                                                   vector and are treated in the same way

                                                                                                momentum
                                                                                        for mathematicallymakes and   theusage
                                                                                                                    mass     reconstruction
                                                                                                 • Reconstruction of decay chains
                                                                                                                 correct           of
                                                                                                                                                                     π-
                                                                                                                                                   of such 4-dimensional       data
           Ω+                                                                                    • Kalman filter based
                        Λ       KFParticle
                              with     timeOmega(K,
                                                stamps Lambda);
                                                            and the covariance        matrices
                                                                                 // construct
                                                                             search              isinteresting
                                                                                           for anti  provided
                                                                                                      Omega by thephysics KF Particle extremely difficult. All of the above
                                                                                                 • Geometry independent
             Ω+                 PV -= (P; Pi; K);                   package based        on the primary
                                                                                  // clean       Kalman filter
                                                                                                 • Vectorized
                                                                                                                  (KF) developed by
                                                                                                             vertex
                              mentioned
                                PV += Omega;
                                                  makes necessary   FIAS group to// 1,2
                                                                                      develop
                                                                                    addprimarily
                                                                                          Omegafor
                                                                                                       fast     and
                                                                                                        CBMprimary
                                                                                                    to the     and      efficient algorithms for data analysis and to
                                                                                                                   ALICE.
                                                                                                                      vertex
                                                                                                                                         Σ-
                                                                                                 • Uncomplicated usage
          ̅ ++
          Ω             Λ̅ K++
                                                          Simulated AuAu collision at 25 AGeV

           Ω̅           Λ̅ K  optimize        them     for
                                Omega.SetProductionVertex(PV);   4. Heavyon
                                                            running
                              ̅̅ ππ+ (K; Lambda).SetProductionVertex(Omega);
                               +                                Functionality:
                                                                               mathematics
                                                                                  a
                                                                                 //    modern
                                                                                    Omega     is requires
                                                                                                 fully        fast and vectorized computer
                                                                                                       high-performance
                                                                                                        fitted
                                                                      algorithms.// K, Lambda are fully fitted
                                                                                                                                                    cluster [3].     n
                             pp                                    • Construction of short-lived particles
                                                                     5. Mother
                                      (P; Pi).SetProductionVertex(Lambda);
                                                                     • Addition       and
                                                                                        // p,daughter
                                                                                and subtraction pi  are fullyparticles
                                                                                                of particles  fitted are KFParticle and
                             2. First Level Event are                                     treated in the same way.
      KFParticle Lambda(P, Pi);                       // construct anti Lambda
      Lambda.SetMassConstraint(1.1157);                // improve momentum and mass  Selection   • Transport
      KFParticle Omega(K, Lambda);            KF Particle provides
                                                      // construct anti Omega    6. aThesimple
                                                                                             naturaland and direct     approach
                                                                                                                   simple             to physics
                                                                                                                                interface
                                                                                                 • Calculation of an angle between particles     allowsanalysis
                                                                                                                                                             to       (used in CBM, ALICE, STAR and sPHENIX)
      PV -= (P; Pi; K);
      PV += Omega;
                             The First Level Event Selection
                                                       // clean the primary vertex
                                                      // add Omega to the primary vertex
                                                                                                          (FLES)            package    decay[4,
                                                                                                 • Calculation of distances and deviations
                                                                                     reconstruct easily       rather complicated                chains.5] of the CBM experiment is intended to
                      Ivan Kisel, Uni-Frankfurt, FIAS, GSI
      Omega.SetProductionVertex(PV);                  // Omega is fully fitted
                                                                                                 • Constraints on mass, production point and decay length                          WWND, Puerto Vallarta, 02.03.2020                             9 /20
                             reconstruct online the7.full
      (K; Lambda).SetProductionVertex(Omega);         // K, Lambda are fully fitted
                                                                                     The package
                                                                                            event istopologygeometry independent
                                                                                                 • KF Particle Finder         including        and tracks
                                                                                                                                                      can be        of charged particles and short-lived
      (P; Pi).SetProductionVertex(Lambda);            // p, pi are fully fitted      easily adapted to different experiments.
                             particles. The FLES package consists of several modules: Cellular Automaton (CA) track finder,
                            KFParticle provides uncomplicated approach to physics analysis (used in CBM, ALICE and STAR)
   1. KF Particle — S. Gorbunov, “On-line reconstruction algorithms for the CBM and ALICE experiments,” Dissertation thesis, Goethe University of Frankfurt, 2012,
                             kalman Filter (KF) track fitter, KF Particle Finder and physics selection. In addition, a quality
   http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/29538
V. Akishina, I. Kisel, Uni-Frankfurt, FIAS                                                                               MMCP 2017, Dubna, 07.07.2017 11 /16
   2. KF Particle Finder — M. Zyzak, “Online selection of short-lived particles on many-core computer architectures in the CBM experiment at FAIR,” Dissertation
   thesis, Goethe University of Frankfurt, 2016, http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/41428
  20 July 2018
                             check module is implemented,             STAR Collaboration Meeting
                                                                                                     that allows to monitor and                              2 /18
                                                                                                                                                                   control the reconstruction process at
                             all stages. The FLES package is platform and operating system independent. The package is
                             portable to different many-core CPU architectures, vectorized using SIMD (Single Instruction,
                             Multiple Data) instructions and parallelized between CPU cores. All algorithms are optimized
                             with respect to the memory usage and the speed.

                                                                                                                                                                           2
Real-Time Event Reconstruction and Analysis in CBM and STAR Experiments - IOPscience
36th Winter Workshop on Nuclear Dynamics                                                                             IOP Publishing
Journal of Physics: Conference Series                            1602 (2020) 012006            doi:10.1088/1742-6596/1602/1/012006

2.1. Cellular Automaton (CA) track finder
The 4-dimensional (4D, space and time) Cellular Automaton (CA) track finder [5, 6] takes as
input hit measurements from the tracking detector in the form of a time-slice, which includes
time and spacial measurements. The track finding procedure starts with combining the hits
into triplets, combination of three hits on adjacent stations. The triplet structure was chosen,
since it allows to estimate the momentum of a particle, which could produce it. The triplets
with two common hits are combined into track candidates. The track candidates should survive
a dedicated selection based on the track length and calculated χ2 -value to be accepted to the
reconstructed tracks.
   Input time information is used in the algorithm to the same extent and in similar manner
as it is done with the spacial coordinates. The same logic is used while constructing triplets:
the hits in the triplet should belong to the same particle, therefore they should correlate not
only in space, but also in time. The resulting track reconstruction efficiencies for the cases of
event-by-event analysis (so-called 3D analysis) as well as for the 4D case (with included time
measurement, as well as 3-dimensional spacial information) while reconstructing time-slices are
similar thus there is no efficiency degradation in the much more complicated case of time slices.
                              4D ofEvent
The same is valid for the speed      the 4DBuilding     at 10with
                                            CA tracks finder   MHzrespect to the 3D case.

2.2. Kalman Filter (KF) track fit
High precision of the parameters of particle trajectories (tracks) and their covariance matrices
is aHitsprerequisite
         at high input rates for finding rare signal events among hundreds of thousands of background
events.      Such high precision is usually
    Hits 0.1 MHz                                      obtained by using the estimation
                                             Hits 1 MHz                       Hits 10 MHz
                                                                                          algorithms based on
the Kalman filter (KF) method. High speed of the reconstruction algorithms on modern many-
core computer architectures can be accomplished by: optimizing with respect to the computer
memory, in particular declaring all variables in single precision, vectorizing in order to use the
SIMD instruction set and parallelizing between cores within a compute node.

2.3. 4D event builder
    From hits to tracks to events

     (1) Hits 10 MHz                                (2) Tracks                                      (3) Events

Figure 2. Reconstructed tracks in time slices clearly represent groups, which correspond to the
                               Reconstructed tracks clearly represent groups, which correspond to the original events:
original events       85%with      85%
                             of single    of single
                                       events,           events,
                                               no splitted          no splitted
                                                           events, further           events,
                                                                           analysis with        and final
                                                                                         TOF information      event
                                                                                                         at the        building
                                                                                                                vertexing stage       is done at
the   vertexing stage using TOF information.
 Ivan Kisel, Uni-Frankfurt, FIAS, GSI                                                                      WWND, Puerto Vallarta, 02.03.2020 8 /20

   After all tracks are found and their parameters are reconstructed, the tracks are grouped
into events. This is done by clustering tracks based on their time parameters in the area of the
target. The left distribution of Fig. 2 shows hits within a time slice for 107 interaction rate. One
can see that the traditional grouping of hits into events at this stage is impossible. The track
distribution at the middle shown against the same hits displays grouping of tracks belonging to
the same event. The right distribution with different colors shows different clusters of tracks,
close in time in the target area. One can see that already at this stage it is possible to build
events with efficiency more than 85%. The task of event building is finalized at the stage of

                                                                         3
Real-Time Event Reconstruction and Analysis in CBM and STAR Experiments - IOPscience
36th Winter Workshop on Nuclear Dynamics                                                                                                                 IOP Publishing
Journal of Physics: Conference Series                                               1602 (2020) 012006                             doi:10.1088/1742-6596/1602/1/012006

searching the primary vertex, where it is possible to additionally use the proximity of tracks in
space, as well as more accurate time measurements of the TOF detector.

2.4. KF Particle Finder — a package for reconstruction of short-lived particles
Today the most interesting physics is hidden in the properties of short-lived particles, which
are not registered, but can be reconstructed only from their decay products. A fast and
efficient KF Particle Finder package [4, 7], based on the Kalman filter (hence KF) method,
for reconstruction and selection of short-lived particles is developed to solve this task. A search
of more4 than 100KF
                  decay channels
                     Particle     has been
                                Finder       currently
                                         forFinder
                                              Physics  implemented
                                                         Analysis and(Fig.Selection
                                                                           3).
                              KF  Particle          block-diagram
                                                                       Charged particles: e±, µ±, π±, K±, p±, d±, 3He±, 4He±

                                                                          Neutral particles: νµ, ν̅µ, π0, n, n̅ , Λ, Λ̅, Ξ0, Ξ̅0

                       Dileptons              Open-charm                                                Strange particles                                            Hypermatter

                      Charmonium                                              K0s → π+ π-
                                                Open-charm                    K+ → µ+ νµ                                                                          Hypernuclei
                      J/ψ → e+ e-
                                                  particles                                                                                                    {Λn} → d+ π-
                      J/ψ → µ+ µ-                                             K- → µ- ν̅µ                  Ξ- → Λ π-
                                             D0   → K- π+                                                                                                      {Λ̅n̅ } → d- π+
                                                                              K+ → π+ π0                   Ξ̅+ → Λ̅ π+
                       Low mass              D0 → K- π+ π+ π-                                                                                                  {Λnn} → t+ π-
                                                                              K- → π- π0                   Ξ- → Λ π-               Σ+     → p π0
                     vector mesons           D̅ 0 → K+ π-                                                                                                      {Λ̅n̅ n̅ } → t- π+
                                                                                                           Ξ̅+ → Λ̅ π+             Σ̅-    → p̅ π0
                      ρ → e+ e-              D̅ 0 → K+ π+ π- π-               Λ → p π-                                                                          3 H → 3He π-
                                                                                                                                                                 Λ
                                                                                                           Ω- → Λ K-               Σ0     →Λγ
                      ρ → µ+ µ-              D+ → K- π+ π+                    Λ̅ → p̅ π+                                                                         Λ ̅
                                                                                                                                                                3 H       → 3He π+
                                                                                                           Ω̅+ → Λ̅ K+             Σ̅0    → Λ̅ γ
                      ω → e+ e-              D- → K+ π- π-                    Σ+ → p π0                                                                         4 H → 4He π-
                                                                                                                                                                 Λ
                                                                                                           Ω- → Λ K-               Ξ0     → Λ π0
                      ω → µ+ µ-              Ds+ → K+ K- π+                   Σ̅- → p̅ π0                                                                        Λ ̅
                                                                                                                                                                4 H       → 4He π+
                                                                                                           Ω̅+ → Λ̅ K+             Ξ̅0    → Λ̅ π0
                      ϕ → e+ e-                                               Σ+ → n π+
                                                                                                                                                               4 He → 3He p π-
                                                                                                                                                                Λ
                                             Ds- → K+ K- π-                                                Ω- → Ξ0 π-
                      ϕ → µ+ µ-                                                                                                                                4 He → 3He p π+
                                                                                                                                                                Λ                 ̅
                                             Λc+→ p K- π+                     Σ̅- → n̅ π-                  Ω̅+ → Ξ̅0 π+                                        5 He → 4He p π-
                                                                                                                                                                Λ
                                             Λ̅c- → p̅ K- π+                  Σ- → n π-                                                                        5 He → 4He p π+
                                                                                                                                                                Λ                   ̅
                         Gamma                                                Σ̅+ → n̅ π+
                        γ → e+ e-
                    Gamma-decays                                                                      Strange resonances
                      π0 → γ γ                                                                                                                                      Double-Λ
                      η →γγ                                                                                                                                        hypernuclei
                                                                                                                                                               4
                                                                                                         Ξ*0 → Ξ- π+                                            ΛΛH  → 4ΛHe π-
                                                                                                                                                               4 H → 3 H p π-
                                                                             K*+    → K0s π+             Ξ̅*0 → Ξ̅+ π-                                          ΛΛ       Λ
                     Light mesons                                                                        Ω*- → Ξ- K- π+            K*+    → K+ π0              5 H → 5 He π-
                                                                                                                                                                ΛΛ       Λ
                     and baryons              Open-charm                     K*-    → K0s π-                                                                   4 He → 5 He p π+
                                                                                                         Ω̅*+ → Ξ̅+ K+ π-          K*-    → K- π0               ΛΛ       Λ
                                                resonances                   Σ*+    → Λ π+                                         K*0    → K0 π0
                      π+     → µ+ νµ          D*0 → D+ π-                    Σ̅*-   → Λ̅ π-                                        Σ*0    → Λ π0
                      π-     → µ- ν̅µ         D̅ *0 → D- π+                  Σ*-    → Λ π-                                         Σ̅*0   → Λ̅ π0
                      ρ      → π+ π-          D*+ → D0 π+                    Σ̅*+   → Λ̅ π+               K*0     → K+ π-          Ξ*-    → Ξ- π0                    Heavy multi-
                      Δ0     → p π-           D*- → D̅ 0 π-                  Ξ*-    → Λ K-                K̅ *0   → K- π+          Ξ̅*+   → Ξ̅+ π0                  strange objects
                      Δ̅0    → p̅ π+                                         Ξ̅*+   → Λ̅ K+               ϕ       → K+ K-
                                                                                                                                                                   {ΛΛ} → Λ p π-
                      Δ++    → p π+                                                                       Λ*      → p K-
                      Δ̅--   → p̅ π-                                                                      Λ̅*     → p̅ K+                                          {Ξ0Λ} → Λ Λ

                                                                                                                                           ( mbias: 1.4 ms; central: 10.5 ms )/event/core
           23 March 2017                                      Maksym Zyzak, 29th CBM Collaboration Meeting, Darmstadt                                                                   3 /15
      Ivan Kisel, Uni-Frankfurt, FIAS, GSI                                                                                                          WWND, Guadeloupe, 28.03.2018 !10 /18
Figure 3. Block diagram of the KF Particle Finder package. The particle parameters, such as
decay point, momentum, energy, mass, decay length and lifetime, together with their errors are
estimated using the Kalman filter method.

   In the package all registered particle trajectories are divided into groups of secondary and
primary tracks for further processing. Primary tracks are those, which are produced directly
in the collision point. Tracks from decays of resonances (strange, multi-strange and charmed
resonances, light vector mesons, charmonium) are also considered as primaries, since they are
produced directly at the point of the primary collision. Secondary tracks are produced by the
short-lived particles, which decay not in the point of the primary collision and can be clearly
separated. These particles include strange particles (Ks0 and Λ), multi-strange hyperons (Ξ and
Ω) and charmed particles (D0 , D± , Ds± and Λc ). After that tracks are combined according to
the block diagram in Fig. 3. The package estimates the particle parameters, such as decay point,
momentum, energy, mass, decay length and lifetime, together with their errors. The package has
a rich functionality, including particle transport, calculation of a distance to a point or another
particle, calculation of a deviation from a point or another particle, constraints on mass, decay
length and production point. All particles produced in the collision are reconstructed at once,
that makes the algorithm local with respect to the data and therefore extremely fast.
   In addition, simultaneous reconstruction in the KF Particle Finder of different decay channels
of the same particle, including also decays with a neutral particle in the final state, makes it

                                                                                                4
Real-Time Event Reconstruction and Analysis in CBM and STAR Experiments - IOPscience
36th Winter Workshop on Nuclear Dynamics                                                                                                                                        IOP Publishing
      Journal of Physics: Conference Series                                                                   1602 (2020) 012006                                doi:10.1088/1742-6596/1602/1/012006

                             Clean Probes of Collision Stages
       possible to calculate the efficiency of the reconstruction of rare particles and reliably estimate
       their systematic errors.

                                      ×106                          0
                                                                   Ks σ = 3.6 MeV/c2                   ×106                    Λ σ = 1.6 MeV/c2                                               Λ σ = 1.4 MeV/c2
                     Entries

                                                                                        Entries

                                                                                                                                                      Entries
                                                                   S/B = 42.6                                                  S/B = 89.7                                                     S/B = 8.73

                                                                                                   5                                      -
                                 1                        K0s→π+π-                                                        Λ→ pπ                            500
                                                                                                                                                                                        Λ→pπ+

                                 0                                                                 0                                                            0
                                                   0.5                            0.6                         1.1                   1.2                                     1.1                        1.2
                                                     minv {π+π-} [GeV/c2]                                             minv {pπ-} [GeV/c2]                                          minv {pπ+} [GeV/c2]
                                      ×103                          -
                                                                   Ξ σ = 1.9 MeV/c2
                                                                                                                                +
                                                                                                                               Ξ σ = 1.7 MeV/c2
                                                                                                                                                                                               -
                                                                                                                                                                                              Ω σ = 2.1 MeV/c2
                     Entries

                                                                                        Entries

                                                                                                                                                      Entries
                                20                                 S/B = 14.1                                                  S/B = 10.7                  200                                S/B = 35.3
                                                                                                  20

                                                               -                  -                                        +                                                              -                  -
                                                          Ξ →Λπ                                                           Ξ →Λπ+                                                        Ω →ΛK
                                10                                                                                                                         100
                                                                                                  10

                                 0                                                                 0                                                            0
                                             1.3                            1.4                               1.3                   1.4                         1.6                     1.7                      1.8
                                                                        -                                                                                                                          -
                                                     minv {Λπ } [GeV/c2]                                             minv {Λπ+} [GeV/c2]                                           minv {ΛK } [GeV/c2]

                                      ×106                -
                                                         Σ σ = 5.9 MeV/c2                              ×103           Σ+ σ = 5.5 MeV/c2                              ×103           Σ+ σ = 11.1 MeV/c2
                      Entries

                                                                                        Entries

                                                                                                                                                      Entries
                                                         S/B = 49.7                                                   S/B = 7.21                                20                  S/B = 5.81
                               0.2                                                                40

                                                               -
                                                              Σ →π-n                                                      Σ+→π+n                                                        Σ+→pπ0
                                0.1                                                               20                                                            10

                                 0                                                                 0                                                             0
                                 1.1                1.2                     1.3                    1.1              1.2             1.3                          1.1              1.2                  1.3
                                                         minv {π-n} [GeV/c2]                                         minv {π+n} [GeV/c2]                                            minv {pπ0} [GeV/c2]
                                                                                                                                                  5M central AuAu UrQMD events at 10 AGeV with realistic PID

Ivan Kisel, Uni-Frankfurt,
        Figure       4. The    package provides clean probes of various stages WWND,
                           FIAS, GSI
                                  FLES                                         of thePuerto Vallarta, 02.03.2020
                                                                                      collision:       results of14 /20

       the search for short-lived particles are shown for 5M central AuAu UrQMD events at 10 AGeV
       with realistic PID.

          The use of the Kalman filter at all stages of particle reconstruction allows in many cases to
       get rid almost completely of the combinatorial background and to obtain clean sets of particles,
       which can serve as probes of various stages of the collision (Fig. 4).

       2.5. Deep learning for quark-gluon plasma detection
       In addition to the macroscopic inverse approach [8] we investigate the microscopic inverse
       approach by using artificial neural networks to classify processes in heavy ion collisions. We
       have created two types of neural networks: fully connected (FC) and deep convolutional (CNN)
       neural networks. These networks were then used to identify quark-gluon plasma simulated
       within the Parton-Hadron-String Dynamics (PHSD) microscopic off-shell transport approach
       for central Au+Au collision at a fixed energy.
          For FC networks we use a 64-neuron fully-connected hidden layer with batch normalization,
       Leaky Rectified Linear Unit (LReLU) activation and dropout. The number of neurons is chosen
       empirically and is fixed to allow comparison of FC neural networks with one, two and three
       layers. Batch normalisation and dropout are used to reduce overfitting and therefore improve
       overall performance. LReLU is used as it performs similarly to the most commonly used Rectified
       Linear Unit (ReLU) activation function but avoids dead neuron issues.
          The CNN consists of two three-dimensional convolutional layers, each followed by a max
       pooling layer, and two sequential fully-connected layers.

                                                                                                                          5
Real-Time Event Reconstruction and Analysis in CBM and STAR Experiments - IOPscience
theory.gsi.de/~ebratkov/phsd-project/
                                                                                                                                                                                       Input (28x20x20x20)
                                                                                                                                     2-layer fully-connected network
                                                                                                                                                                                   Conv3D (32, 3x3x3, LReLU)
                                                                                                                                               Input (28x20x20x20)

:                                                             PHSD model                                                                                                               Max pooling (2x2x2)
       Collision:
     September  29, 2019          7:56    WSPC/INSTRUCTION FILE                       ”Deep learning for                                                Flatten
                                                                                                                                                                                   Conv3D (64, 3x3x3, LReLU)
    QGP ●    Au+Au
         detection”
                                 QGP off on Nuclear
         ● Central 36th Winter Workshop             QGP  on
                                                     Dynamics
                                                                                                                                        FC (64, bn, LReLU, dropout 0.5)
                                                                                                                                                                                 IOP     Publishing
                                                                                                                                                                                  Max pooling (2x2x2)

                               5000 events        5000 events                                                                                      FC (2, Softmax)
         ● 31.2A GeV
                   Journal of Physics: Conference Series                                                    1602 (2020) 012006                             doi:10.1088/1742-6596/1602/1/012006
                                                                                                                                                                                        Flatten

                                                                                                                                          QGP off                 QGP on
                               How to classify an event?                                                                                                                          FC (64, bn, LReLU, dropout 0.5)

                8        F. Sergeev, E. Bratkovskaya, I. Kisel and I. Vassiliev                                                                                                           FC (2, Softmax)

                                                                                                                                                                                   QGP off                 QGP on
                                                     CBM Collaboration Meeting, Kolkata, 01.10.2019 6 /12

                                                                                                                         Architecture                                Accuracy
                                                                                                                 Ivan Kisel, Uni-Frankfurt, FIAS, GSI                               CBM Collaboration Meeting, Kolkata, 01.10.2019 9 /12

                                                                                                                                                 1-layer                   ~80%

                                                                                                                     FC  NN 5.
                                                                                                                      Figure       Training ~80%
                                                                                                                               2-layer      and validation accuracy
                                                                                                                      for the FC networks and the CNN.
                                                                                                                               3-layer      ~75%

                                                                                                                                    CNN                                    >90%

                               Fig. 5.                     Goalaccuracy
                                         Training and validation is to determine      physical
                                                                        for the FC networks      properties
                                                                                            and the CNN.                of QCD matter in real time
      Ivan Kisel, Uni-Frankfurt,
                             The FIAS, GSI5
                                    Fig.    shows that the accuracy on the validation set rapidly increases        WWND, Puerto
                                                                                                                          for allVallarta, 02.03.2020
                                                                                                                                  four network                                                                              17 /20
                4. Conclusion
                        architectures
                The results obtained in ourupworktosuggest
                                                      the fifth     epoch,
                                                             that raw         whenhidden
                                                                       data contains   the patterns
                                                                                            rise slows down and the curves level off. At the
                        same
                that allow       time,network
                           the neural    the precision         on thean training
                                                classifiers to discern                 set using
                                                                           event simulated  continues
                                                                                                 the  to go up until it reaches 100%, which
                transport model with and without the quark-gluon plasma formation model. Out
                        suggests that overfitting occurs after the fifth epoch. Nevertheless, the fully-connected networks
                of four architectures that included several fully-connected networks as well as a
                        reachneural
                convolutional    80%network
                                        precision     while
                                              the latter       the
                                                          showed  theconvolutional
                                                                      best performance. neural network attains the best performance of more
                        than 90% accuracy.
                Acknowledgments
                        3. Express
                Fedor Sergeev             reconstruction
                              is thankful to                       andStudent
                                             the International Summer    analysis
                                                                                Programinat STAR
                                                                                             GSI-
                FAIR for the opportunity to participate in the Summer School in 2019.
                        The STAR (Solenoidal Tracker At RHIC) experiment [9] at the RHIC (Relativistic Heavy Ion
                   The work was supported in part by the Helmholtz International Center for FAIR
                (HIC forCollider)    facility
                         FAIR), the Hessen  Stateof  the of
                                                  Ministry  Brookhaven       National
                                                              Higher Education,            Laboratory
                                                                                Research and  the     (BNL, USA) is designed to study
                        nuclearandmatter
                Arts (HMWK),                  under
                                     the Federal        extreme
                                                  Ministry          conditions
                                                            of Education           of relativistic
                                                                         and Research  (BMBF),     heavy ion collisions, including hadron
                Germany.production and search for signs of quark-gluon plasma formation and its properties.
                                  Very important for RHIC is the possibility to collide ions, covering the range of baryon
                References
                              chemical potential (µB ) from 20 to 420 MeV, which corresponds to a wide range of energies
                    1.    K. Fukushima and T. Hatsuda, Rept. Prog. Phys. 74 014001 (2011).
                    2.    The (so
                              CBM called      Beam
                                    collaboration.      EnergyetScan,
                                                   (T. Ablyazimov  al.), Eur.BES).     The BES results once again confirmed evidence of QGP
                                                                              J. Phys. A
                                                                                    √ 53, 60 (2017).
                              discovery in the upper RHIC energy sN N = 200 GeV. The results of the search for the critical
                              point and the first-order phase boundary have narrowed the region of interest to collision energies
                                        √
                              below sN N = 20 GeV. Thus, the phase II of the Beam Energy Scan (BES-II), scheduled for
                                                                                           √
                              2019-2020 [10], covers the energy range sN N
Real-Time Event Reconstruction and Analysis in CBM and STAR Experiments - IOPscience
36th Winter Workshop on Nuclear Dynamics                                                                                                   IOP Publishing
Journal of Physics: Conference Series                                          1602 (2020) 012006                    doi:10.1088/1742-6596/1602/1/012006

used in HLT and its integration into the official STAR repository for use in the standard physics
analysis is currently in progress.
                       BES-II: eXpress+Standard Data Production and Analysis
                 2019, 2020                           DAQ                                Disk                    Tape
                                                  ?            „good“
                 tHLT = tDAQ + 1s                     HLT                                     Tape
                 tHLT = tDAQ + 1s
                                   xHLT                                                                  oRCF
                                                      Disk           xCalibration             Disk
                 txCal = tDAQ + 1w
                 txCal = tDAQ + 1h
                                                                          DB
                                                               30%                  70%
                 txProd = txCal + 1w             xProduction                          xProduction
                 txProd = txCal + 1d
                                             CA Track Finder                        CA Track Finder

                 txPhys = txProd                  xPhysics                             xPhysics                  xStorage
                 txPhys = txProd
                                             KF Particle Finder                     KF Particle Finder

                                                                                         Disk

                 tCal = tRun + 1m                              DB                     Calibration
                                                                                                                 Disk

                 tProd = tCal + 6m                                                                          Production                        Tape
                                                                                                            StiCA Track Finder

                                                                                                                                               Disk
                                                                        tRun   tCal      tProd tPhys
                                                   tBES-II = 2020 + 6 m + 1 h + 1 d + 3 m = 6÷9 m = 2020                                    Physics
          time

                 tPhys = tProd + 6m
                 txPhys = txProd + 3m              tBES-II = 2020 + 6 m + 1 m + 6 m + 6 m = 1÷2 y = 2020÷2021
                                                                                                                                          PWG Standard,
                                                   tBES-II = 2020 + 6 m + 2 m + 1 y + 1 y = 2÷3 y = 2022÷2023                       KF Particle, KF Particle Finder
          Ivan Kisel, Uni-Frankfurt, FIAS, GSI                                                                             WWND, Puerto Vallarta, 02.03.2020 19 /20

    Figure 6. The HLT express and the standard data production and analysis workflows.

    The use of the CA track finder and the KF particle finder in online extends significantly
the functionality of HLT (Fig. 6). The standard calibration, production and analysis remain
unchanged. HLT starts the calibration procedure as soon as data become available. The express
chain makes possible physics analysis of the data as soon as the calibration is reasonable. It
unifies approaches in extended (x)HLT and online (o)RCF to speed up the express workflow,
and combines high competence of xHLT and oRCF experts involved in online operation. In
addition, it provides physics working groups with instant and uncomplicated access to the data,
like picoDST etc.
    With the express calibration and alignment one can reconstruct hyperons with high
significance and low level of background, as it is shown in Fig. 7. Hyperons are clearly seen
at all BES-II energies: 3, 3.2, 3.9, 7.7, 9.1, 14.5, 19.6, 27 GeV. In addition, high significance
allows extraction of spectra.

4. Conclusion
The CBM experiment with 107 input rate will require the full event reconstruction and physics
analysis of the experimental data online. As the same HPC farm will be used for offline and online
processing of experimental data, the main reconstruction and analysis algorithms will work both
offline and online. Errors and insufficient accuracy in online data processing, physics analysis
or selection of interesting collisions by the reconstruction algorithms will lead to complete loss
of all experimental data, since only the incorrectly selected data will be stored in this case.
Therefore only immediate comparison of the results of online analysis with the predictions of
theoretical models using ANNs can guarantee the proper operation of the whole experiment. It
has been demonstrated, that the core algorithms of the FLES package, the Cellular Automaton
for searching for particle trajectories (100 µs/core/track) and the Kalman Filter to estimate
their parameters (0.5 µs/core/track), have a very high level of intrinsic parallelism for their fast

                                                                                          7
36th Winter Workshop on Nuclear Dynamics                                                                                                                  IOP Publishing
Journal of Physics: Conference Series                                                            1602 (2020) 012006                 doi:10.1088/1742-6596/1602/1/012006
                                                                           BES-II: xHyperons
                                                             200M AuAu events at 14.5 GeV, 2019 BES-II express production
                                  6                                                         6                                                    3
                Entries        ×10 M = 1116.0 MeV/c2 σ = 1.7 MeV/c2                      ×10 M = 1322.3 MeV/c2 σ = 2.1 MeV/c2                 ×10 M = 1672.7 MeV/c2 σ = 2.2 MeV/c2

                                                                         Entries

                                                                                                                                Entries
                                                                                                                                          4
                          20          S/B = 15.1 S/ S+B = 7468.9                                S/B = 9.16 S/ S+B = 1046.5                           S/B = 3.62 S/ S+B = 73.9
                                                         -                         0.5                     -          -                                         -          -
                                               Λ→ pπ                                                     Ξ →Λπ                                               Ω →ΛK
                          10                                                                                                              2

                          0                                                         0                                                     0
                               1.1                       1.15                        1.3                       1.35                       1.65                  1.7             1.75
                                                                                                                  -                                                    -
                                               minv {pπ-} [GeV/c2]                                      minv {Λπ } [GeV/c2]                                  minv {ΛK } [GeV/c2]
                                  6                                                         3                                                    3
                               ×10 M = 1116.0 MeV/c2 σ = 1.6 MeV/c2                      ×10 M = 1322.4 MeV/c2 σ = 2.2 MeV/c2                 ×10 M = 1672.9 MeV/c2 σ = 2.3 MeV/c2
                Entries

                                                                         Entries

                                                                                                                                Entries
                          2           S/B = 7.36 S/ S+B = 2290.1                                S/B = 14.4 S/ S+B = 475.7                            S/B = 7.35 S/ S+B = 52.8
                                                                               100                        +                                                    +
                                                         +
                                               Λ→pπ                                                     Ξ →Λπ         +
                                                                                                                                                             Ω →ΛK+
                                                                                                                                          1
                           1
                                                                                   50

                          0                                                         0                                                     0
                               1.1                       1.15                        1.3                       1.35                       1.65                  1.7             1.75
                                              minv {pπ+} [GeV/c2]                                       minv {Λπ+} [GeV/c2]                                 minv {ΛK+} [GeV/c2]

            •   With the express calibration and alignment we reconstruct hyperons with high significance and low level of background.
Figure 7.    Online
        • Hyperons        search
                     are clearly seen for
                                      at all hyperons
                                             BES-II energies:on   200M
                                                              3, 3.2, 3.9, 7.7,AuAu
                                                                                9.1, 14.5, events    at 14.5 GeV (2019 BES-II express
                                                                                           19.6, 27 GeV.
production).
        • High significance  allows extraction of spectra.

         Ivan Kisel, Uni-Frankfurt, FIAS, GSI                                                                                                   WWND, Puerto Vallarta, 02.03.2020 19 /20

and efficient implementation on many-core CPU/GPU architectures. The KF particle finder
package with more than 150 decay channels implemented (100 µs/core/decay) is a common
platform for offline physics analysis and for real-time express analysis at 107 interaction rate in
CBM.
   Adaptation of the FLES algorithms within the FAIR Phase-0 program to the STAR
experiment with its excellent detector performance, high quality experimental data and a well
established reconstruction chain is the first and successful step in preparing the FLES algorithms
for reconstruction and analysis of CBM real data at Day-1. Use of the CA track finder and KF
particle finder developed in the CBM experiment can be beneficial for other experiments as the
experimental heavy ion physics becomes more and more challenging.

References
[1] FAIR — Facility for Antiproton and Ion Research. Green Paper. The Modularized Start Version. GSI. October
       2009.
[2] CBM Collaboration, Compressed Baryonic Matter Experiment, Tech. Stat. Rep., GSI, Darmstadt, 2005; 2006
       update.
[3] I. Kisel, Event reconstruction in the CBM experiment, Nucl. Instr. and Meth. A566 (2006) 85-88.
[4] I. Kisel, I. Kulakov and M. Zyzak, Standalone first level event selection package for the CBM experiment,
       IEEE Trans. Nucl. Sci. 60 (5) (2013) 3703-3708.
[5] V. Akishina and I. Kisel, Online 4-dimensional reconstruction of time-slices in the CBM experiment, IEEE
       Trans. Nucl. Sci. 62 (6) (2015) 3172-3176.
[6] V. Akishina, “4D Event Reconstruction in the CBM Experiment”, Dissertation thesis, Goethe university,
       Frankfurt am Main (2017).
[7] M. Zyzak, “Online Selection of Short-Lived Particles on Many-Core Computer Architectures in the CBM
       Experiment at FAIR”, Dissertation thesis, Goethe university, Frankfurt am Main (2016).
[8] I. Kisel, Event Topology Reconstruction in the CBM Experiment, J. Phys. Conf. Ser. 1070 (2018), 97.
[9] K.H. Ackermann et al. (STAR Collaboration), “STAR detector overview”, Nucl. Instr. Meth. A499 (2003)
       624.
[10] STAR Collaboration, “Studying the Phase Diagram of QCD Matter at RHIC”, 01 June 2014.
       https://drupal.star.bnl.gov/STAR/files/BES WPII ver6.9 Cover.pdf

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