GVD - Neutrino Telescope in Lake Baikal - DESY Indico
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Winter expedition at Lake Baikal
GVD - Neutrino Telescope in Lake Baikal
Present and Nearest Future
Lukáš Fajt
IEAP CTU in Prague
For the Baikal-GVD Collaboration
EPS-HEP 2021
29. 07. 2021
L. Fajt Baikal-GVD 29.07.2021 1 / 18
Neutrino Astronomy
Neutrinos:
are stable
are not effected by electric and
magnetic fields
do not scatter on gas, dust and CMB
escape easily from dense environments
can track sources of HE cosmic rays
and/or γs
arXiv:1111.0507
L. Fajt Baikal-GVD 29.07.2021 2 / 18
Present L. Fajt Baikal-GVD 29.07.2021 2 / 18
Neutrino Telescope Baikal-GVD
Neutrino telescope Baikal-GVD (Gigaton Volume Detector) is a cubic-kilometre scale underwater 3D array of
photon-sensitive PMTs whose main purpose is the study of astrophysical neutrinos
10 organizations,5 countries, 70 members
3.6 km from shore
Lake depth 1366 m
Absorption length: 22 m
Scattering length: 30-50 m
Ice coverage for 2 months
Moderately low background (15-80 kHz)
2016: First cluster
2021: eight clusters, 2304 OMs
L. Fajt Baikal-GVD 29.07.2021 3 / 18Optical Module (OM) = Basic Detection Unit
L. Fajt Baikal-GVD 29.07.2021 4 / 18Cluster = Basic Construction Unit
Cluster:
8 independent strings
60 m radius
Completely independent
Separate electro-optical shore cable
DAQ located in the water (30 m depth)
Trigger conditions:
I 4.5 and 1.5 p.e. on adjacent OMs in 100 ns window
String:
36 OMs, 15 m spacing, depths from 750 to 1275 m
Readout is organised in 3 sections, 12 OMs each
Acoustic and LED calibration devices
Anchored at the lake bottom
Buoys on the top (30 m depth)
L. Fajt Baikal-GVD 29.07.2021 5 / 18Detector Calibrations
Positioning:
Up to 50 m deviations of top OMs
Average velocity 0.5 cm/s
Measurements every 1-6 minutes
Positioning precision < 20 cm
Time Calibration:
Precise timing crucial for high angular reconstruction
precision
3 types of calibration devices: Built-in LEDs, LED
beacons, lasers
Time calibration precision < 2 ns
Intercluster calibration with WR + laser
L. Fajt Baikal-GVD 29.07.2021 6 / 18Automatic Data Processing
https://pos.sissa.it/395/1040/pdf
40 Gb/cluster/day send and stored at the shore
centre
300 Mbit/s radio link over the lake to Baikalsk
Data send to JINR servers over the internet
Data stored on EOS
Since 2021, completely automatic data processing
(100s of cores) + alert production system
Raw waveforms stored → possible reprocessing
Pulse extractions
White Rabbit synchronization of independent cluster
data flows
Single cluster track and two independent cascade
reconstructions
OM coordinates monitoring
DQM
L. Fajt Baikal-GVD 29.07.2021 7 / 18Muon Tracks Reconstruction
MC Simulations:
Data Sample: Muon Reconstruction:
Simple neutrino generator for CC
interactions of νµ and νµ with Single cluster analysis Hit finding (noise rejection)
Bartol flux model (10 GeV - April 1 and June 30, 2019 Preliminary muon track direction
100 TeV) estimation
Low-noise period
Atmospheric muon bundles: Track fit Q = χ2 (t) + w · f (q, r )
I CORSIKA 5.7 (240 GeV - 2 PeV) ∼ 320 days of single-cluster
I MUM for muon propagation equivalent Neutrino selection
I 643 days of single-cluster livetime I BDT
9.8 million reconstructed events I Cut-based selection
Realistic per-channel noise
https://pos.sissa.it/395/1177/pdf https://pos.sissa.it/395/1080/pdf
L. Fajt Baikal-GVD 29.07.2021 8 / 18Muon Neutrino Sample - Cut Based Selection
Neutrino selection cuts:
Results:
Zenith angle > 120◦
Data: 44 neutrino candidate events were found
At least 8 hits on at least 2 strings
Atmospheric neutrino MC simulation: 43.6 ± 6.6
Fit quality Q/ndf < 32
(stat.) events
Visible track length L > 42 m
Atmospheric muon background is < 1 event
Average distance to OMs < 18 m
Median energy of the neutrino events ∼ 500 GeV
Charge of all hits > 18 p.e.
L. Fajt Baikal-GVD 29.07.2021 9 / 18Muon Neutrino Candidates
L. Fajt Baikal-GVD 29.07.2021 10 / 18High-energy Cascades
Cascade Reconstruction:
Noise suppression with Extended Causality criterion (Purity = 99.6%, Efficiency = 82.7%)
I |ti − tj | < dij /v + δt with all hits with higher charge
I Hit on the neighbouring OMs in the corresponding time window(0, dij /v + 50) ns
I Q > 1.5p.e.
At least 6 hits on at least 3 strings
Initial position and time estimation
→
−
( R ,T ))2
exp
1
PNhit (Timeas −Ti
Series of χ2 fits of position and time: χ2 = Nhit −4 i=0 σt2
, σt = 4 ns
96 independent Likelihood P minimizations with different
Pinitial values:
L = Lhit + Lnonhit = − i log Pi (Qi |Esh , θsh , φsh ) − j
log Pj (0|Esh , θsh , φsh ), where
Pi (Qi |Esh , θsh , φsh ) = Poisson(Qi |Qexp )
L. Fajt Baikal-GVD 29.07.2021 11 / 18∼ 1 PeV Cascade Neutrino Candidate
GVD 2019 112
937 TeV (1200 TeV)
53 hits used for reconstruction
94 meters from central string
Zenith angle 61 degree
L. Fajt Baikal-GVD 29.07.2021 12 / 18Up-going Neutrino Candidates
GVD 2019 114
79 TeV (91 TeV)
49 hits used for the reconstruction
47 meters from central string
Zenith angle 109 degree
GVD 2020 196 - Preliminary
97 TeV
41 hits used for the reconstruction
61 meters from central string
Zenith angle 115 degree
L. Fajt Baikal-GVD 29.07.2021 13 / 18Multi-messenger studies https://pos.sissa.it/395/002/pdf & https://pos.sissa.it/395/946/pdf
IceCube Alerts Follow-Up:
Baikal Alerts: Since September 2020
Since September 2020 22 alerts processed
a few hour delay No coincidences found
Within collaboration Follow-up of multi-wavelength signals:
Antares Alerts Follow-Up: AT2019dsg TDE
Since December 2018 Magnetar SGR 1935+2154 (2 cascades in 5
48 alerts processed degrees)
3 interesting coincidence candidates found and GW170817 - no events (JETP Letters, v.108,
studied issue 12)
Radio-loud blazars
L. Fajt Baikal-GVD 29.07.2021 14 / 18Future L. Fajt Baikal-GVD 29.07.2021 14 / 18
Detector Construction
Status 2021: 8 clusters, 3 laser stations, experimental string
Effective volume 2021: 0.40 km3 (cascade mode)
L. Fajt Baikal-GVD 29.07.2021 15 / 18Future I
MC Simulations
Improvements in the noise rate generation
Run-by-Run simulations with specific noise and threshold conditions (DONE, being tested)
Multicluster simulations of 5 clusters for 2019 (DONE, being tested)
General
Significant improvements in pulse extraction: Pulse fitting, Double Pulse identification, pulse separation
Alerts: Shorten the time from a few hours to a few tens of minutes
https://pos.sissa.it/395/1113/pdf
L. Fajt Baikal-GVD 29.07.2021 16 / 18Future II
Track Channel Cascade Channel
Multicluster Reconstruction Suppression of background cascades with BDT
Scan-Fit Implementation - higher reconstruction Vetoing with other clusters - search for muon
efficiencies track in other clusters
Optimization of cuts for HE tracks Search for High-energy starting events
Likelihood reconstruction - production of Double cascade reconstruction - new algorithm
likelihood tables being tested on MC data
https://pos.sissa.it/395/1063/pdf https://pos.sissa.it/395/1114/pdf
L. Fajt Baikal-GVD 29.07.2021 17 / 18MC Double Cascades - prove of concept
https://pos.sissa.it/395/1167/pdf
L. Fajt Baikal-GVD 29.07.2021 18 / 18Thank you for your attention. L. Fajt Baikal-GVD 29.07.2021 18 / 18
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