News from the ALICE experiment and activities in Catania - Paola La Rocca Riunione gruppo III - CT 31 Maggio 2021

News from the ALICE experiment
and activities in Catania
Paola La Rocca
Riunione gruppo III – CT
31 Maggio 2021

LHC Roadmap - ALICE

 Today ALICE 2

 ALICE 2.1 ALICE 3
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ALICE Strategy for Run 3 and Run 4

 • 50 kHz Pb-Pb event readout rate (previously ~1 kHz in the central barrel)
 • Detector upgrades (LS2 + LS3)
 • Integrated luminosity targets:
 – LPb-Pb = 13 nb-1 @ = 5 - 5.5 TeV + pp reference data set
 – Lp-Pb = 0.6 pb-1 @ = 8 - 8.8 TeV + pp reference data set
 – Lp-p = 200 pb-1 @ = 14 TeV w/ focus on high multiplicity and rare
 signals
 • Interest in a short O-O run

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ALICE Run 3 and Run 4 physics goals
 PHYSICS GAOLS
 • Heavy-flavour mesons and baryons (down to very low pT)
 • Charmonium states
 • Dileptons from QGP radiation and low-mass vector mesons
 • High-precision measurement of light- and hyper-nuclei
 → Need minimum-bias readout at highest possible rate

 IMPLEMENTATION
 1. Untriggered data sample
 2. Improve tracking efficiency and momentum resolution at low-pT (tracking
 granularity, material budget, distance to IP)
 3. Preserve particle identification (PID) - consolidate and speed-up main ALICE PID
 detectors

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ALICE detector upgrades for Run 3

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Upgrade of the ALICE TPC

 Adopted solution: 4-GEM stack as result of intensive R&D,
 combination of standard (140 μm) and large pitch (280 μm) GEM foils
 (Previous detector for Run 1 and Run 2: 72 MWPCs)

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Upgrade of the ALICE TPC

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Upgrade of the ALICE ITS

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Upgrade of the ALICE ITS

 Adopted solution: 10 m2 active silicon area, 12.5×109 pixels, based on the ALPIDE Monolithic Active
 Pixel Sensor (MAPS)
 Layout: 7 layers (inner/middle/outer): 3/2/2

 ✓ Improved resolution
 ✓ Less material
 ✓ Faster readout
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Upgrade of the ALICE ITS
 On-surface commissioning clean room

 OB-BOT

 IB-BOT

 IB-TOP

 OB-TOP

 Track
 candidate
 in OB
 Bottom
 Half-Barrel

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Upgrade of the ALICE ITS

 Activities (past and ongoing) in Catania:
 • R&D charcaterization of pixel sensors (testbeam, lab test)
 • Design of the FPC test system (Electronics service) → outsourcing contract with Dubna (Saccà)
 • Production test of FPCs (CT+ME, Electronics + Advanced Technologies services) from August 2017
 to September 2019
 • ITS2 installation (Advanced Technologies service: Francesco, Antonio)
 • ALICE Commissioning + general commissioning (CT+ME)

 ! The participation
 to some of these
 activities has been
 modified due to
 COVID emergency !
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Future ALICE ITS3 (@ RUN 4)

 Inner Tracking System (ITS3) after LS3
 Can we get closer to the IP? Can we reduce the material?

 Silicon makes up only about 15% of total material
 • Removal of water cooling → possible if power
 consumption is reduced
 • Removal of circuit board (power+data) →
 possible if integrated on chip
 • Removal of mechanical support → benefit from
 increased stiffness by rolling Si wafers

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Future ALICE ITS3 (@ RUN 4)

 Inner Tracking System (ITS3) after LS3
 Can we get closer to the IP? Can we reduce the material?

 Key ingredients:
 • 300 mm wafer-scale chips
 • 65 nm CMOS process
 • thinned down to 20-40 μm (0.02-0.04% X0), making
 them flexible
 • bent to the target radii
 • mechanically held in place by carbon foam ribs

 Bent MAPS work perfectly!

 June 2021: R&D activity on chip characterisation (→ Possible involvement of the Catania team)
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Upgrade: MFT and FIT

 Muon Forward Tracker
 • New high-resolution Si tracker (2.5

Upgrade: Online and Offline (O2) processing

 O2 data handling challenge: 50 kHz Pb-Pb interactions → ~3.5 TB/s continuous raw data

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Detector performance in Run 3

 ITS2:
 • Improved tracking efficiency
 • Improved tracking resolution
 • Pointing resolution 3x better in transverse
 plane (6x along beam axis)

 New TPC ROC:
 • Preserve momentum resolution for TPC +
 ITS tracks
 • Preserve particle identification via dE/dx

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ALICE collaboration and papers

40 countries
170 institutes
1972 members

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ALICE: most striking recent results

 STRONG INTERACTION AMONG HADRONS Nature volume 588, pages232–238 (2020)

 - Between baryons, the strong interaction
 leads to a residual force
 - Dynamics of strong interaction studied by
 scattering hadrons off each hadrons →
 difficult or impossible for unstable hadrons
 - Precise method to obtain the missing
 information on the interaction dynamics
 between any pair of unstable hadrons →
 femtoscopy

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ALICE: most striking recent results

 STRONG INTERACTION AMONG HADRONS

 • Precise measurement of proton-Omega (the rarest
 of hyperons) correlation
 • Clear evidence of an attractive strong interaction
 among the two hadrons
 • Test of the theoretical predictions based on lattice
 gauge theory methods (HAL QCD) for the first time

 → New avenue in nuclear physics

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Data Analyses in Catania

 Light (anti)nuclei production Study of short-lived resonances

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Light (anti)nuclei production

 • Multi-baryon states (up to A=4) are produced in high energy hadronic collisions at the LHC
 • Their production mechanism is still under debate
 • Two classes of phenomenological models: Statistical hadronisation and Coalescence
 • Strong impact on Dark Matter searches in Space

 Analyses carried out in Catania:

 • (anti)3He in Xe-Xe collisions at 5.44 TeV ☺
 • 3
 (anti) He e (anti)d in p-Pb collisions at 8.16 TeV ☺
 → Paper in Collaboration Review (target PLB)
 • (anti)d in pp collisions at 13 TeV as a function of RT ☺
 → Preliminary analysis approved in May

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(anti)d production in pp @ 13 TeV as a function of RT
• Production in small collision systems is
 explored using the underlying event (UE) φ=0 TOWARDS region
 activity Multiplicity dominated by hard
 trigger (jet)
• UE activity quantified by the
 selfnormalized charged particle
 multiplicity: TRANSVERSE region
 Useful observable definition of
 the Underlying Event (UE)
 =
 
• Jet selection: pT leading > 5 GeV/c AWAY region
• Several intervals of RT are selected in order to Momentum conservation
 → contains recoil jet
 distinguish between low and high UE activity
 (low RT↔low UE; high RT ↔ high UE)

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(anti)d production in pp @ 13 TeV as a function of RT

 d/p d/π

• First measurements of (anti)deuteron production in several RT classes
• d-to-p and d-to-pi integrated yields ratio does not depend on RT
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(anti)d production in pp @ 13 TeV as a function of RT

• B2 parameter flat vs pT /A → in agreement with simple coalescence
• Results presented @ SQM2021

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Study of Short-lived resonances

 Short-lived resonances are an ideal tool to:
 • Study QGP properties (lifetime fm/c  fireball lifetime)
 K*± → π± + K0S
 • To investigate re-scattering and regeneration processes
 • Validate theoretical models K0S → π+ + π-

 Analysis ongoing in Catania:
 • Charged K* in pp collisions at 13 TeV in several
 multiplicity classes
 • Excited - Baryon with machine learning
 algorithms
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Multiplicity dependent analysis of K*(892)± production in pp
collisions at √s = 13 TeV
 Systematic uncertainties estimation for LHC16 data sample completed
 SYSTEMATIC SOURCES CONSIDERED: pT distribution of systematic uncertainties for the multiplicity class 30-40%
 ⚫ Primary track selection and PID cut for primary 
 ⚫ Secondary track selection, PID and topological cuts
 for K0S
 ⚫ Primary vertex selection
 ⚫ Signal extraction
 ⚫ Material budget
 ⚫ Hadronic interaction
 ⚫ Global Tracking uncertainty

 ➢ Yields have been computed with different analysis
 parameters (12 in total)
 ➢ One or two variations from default selection criteria
 have been considered, applying them one by one Procedure performed for each multiplicity class (9 in total) →
 (36 in total) 3888 (36x12x9) different K*± pT spectra estimated.

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K*(892)± Results and K*(892)0 Comparison

 ⚫ Good agreement between pT spectra of K*± and K*0
 ⚫ pT spectra get harder with increasing multiplicity → qualitatively similar to heavy-ion collisions
 ⚫ For pT < 5 GeV/c spectra increase from low to high multiplicity classes, while for pT > 5 GeV/c
 same spectral shape for all multiplicity classes → process dominant at low pT
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and dN/dy spectra: full statistics

Increase the statistics by analyzing also LHC17 and LHC18 data sample: in progress
⚫ Perform the systematic study at full statistics;
⚫ Evaluate the comparison with the main models (PYTHIA6, PYTHIA8, EPOS-LHC, and DYPSI).

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Observation of an Excited - Baryon

 • Difficult to find excited states of - baryon Belle Collaboration
 • Only (2250) listed in PDG (mass ~ 600 MeV/c2
 higher than ground state)
 • Many models predict excited - states in the 2000
 MeV/c2 region
 • - (2012) (decaying into 0K- and -K0S) measured
 for the first time from Belle Collaboration

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Observation of an Excited - Baryon
For ALICE indications of - (2012) in pp Test of machine learning techniques (BDT, Neural network,
data at s = 13 TeV etc..) to improve -(2012) identification.

 BDT provides the best result on MC data so far. Signal
 efficiency >98% and residual background

Computing

INFRASTUCTURE STATUS
 Aggiornamento a HTCondor-CE
 • Tutti i nodi sono stati installati ex-novo su CentOS 7
 • Central Manager in un nodo a parte
 • HTCondor e HTCondor-CE in unico nodo
 • WNs su macchine fisiche e non più virtuali
 • VOBOX con HTCondor

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Computing

 INFRASTUCTURE STATUS

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Computing

 Aumentato lo spazio disco
 aggiungendo i nuovi dischi
 huawei, da 800 TB a 1.016 TB

 PON IBISCO:
 • Gara infrastruttura → firma
 contratto (Schneider
 Electric), 5 mesi per i lavori
 • Gara cpu-storage → scaduti
 i termini per la gara, nomina
 commissione
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Backup

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The ALICE detector
 ALICE Central Barrel
 B = 0.5 T solenoid, |η| < 0.9
 2π tracking and PID
 Lowest material budget in central
 rapidity region at the LHC
 ITS: Vertexing and tracking down to very
 low pT, PID
 TPC: Global tracking and PID
 TOF: PID via time-of-flight, trigger
 HMPID: high-momentum hadron PID via
 Cherenkov emission
 TRD: e/π discrimination, trigger

 Muon spectrometer
 3 Tm dipole
 -4 < η < -2.5

 Forward detectors
 V0, T0, FMD, AD, ZDC
 Trigger, timing, multiplicity
 and centrality

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ALICE upgrade

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Analisi dati: studio della produzione di nuclei leggeri

 In collisioni adroniche ad elevate energie vengono prodotti stati multi-barionici (piccole
 percentuali):
 • (anti)nuclei leggeri fino a A=4
 • nuclei con stranezza (ipernuclei)

 In collisioni pp (p-Pb) la resa diminuisce di un fattore  1000 (600) se si aumenta A di un’unità (350 in collisioni PbPb)

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Analisi dati: studio della produzione di nuclei leggeri
 • (anti)3He in XeXe a 5.44 TeV done
 • (anti)3He e (anti)d in collisioni p–Pb a 8.16 TeV done Paper in Collaboration review
 Da sottomettere a Physics Letters B
 • (anti)d vs RT in collisioni pp a 13 TeV done

 PRELIMINARY RESULTS
 Physics Forum approval
 5/05/21

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Analisi dati: (anti)3He in p–Pb 8.16 TeV
 • Resa: (1.15 ± 0.16 (stat) ± 0.13 (syst) ) 10-6
 • Rapporto 3He/p per confronto con modelli

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Analisi dati: (anti)d in p–Pb 8.16 TeV
 • Resa (MB): (1.27 ± 0.01 (stat) ± 0.04 (syst) ) 10-3
 • Rapporto d/p per confronto con modelli

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Analisi dati: (anti)d & (anti)3He in p–Pb 8.16 TeV

• Novità del paper su p–Pb a 8.16 TeV → confronto rapporti nuclei-to-pion con modello CSM
• Accordo solo qualitativo

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Analisi dati: (anti)d in p–Pb 8.16 TeV

 Test modello di coalescenza

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Analisi dati: studio del K(892)* carico

 Il rapporto K*0/K mostra una soppressione ad alte La produzione di K*0 è indipendente dal sistema,
 molteplicità → rescattering delle particelle figlie dall’energia e aumenta con la molteplicità

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Analisi dati: (anti)d in pPb 8.16 TeV

 Test modello di coalescenza

 • Paper proposal– work in progress
 • Analisi future:
 - (anti)d in Pb-Pb a 5.02 TeV (2018) – tesi
 master
 - Transverse event activity

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