Studies of the UPC trigger efficiency of the light-by-light scattering in the ALICE experiment
M. Sharifi Kiasari, M.E. Kolobov
IFJ PAN
What is Light-by-Light scattering?
PRC93 (2016) 044907 PRC93 (2016) 044907
PRL11 (2013) 080405
M. Sharifi Kiasari, M.E. Kolobov (IFJ PAN) Studies of the UPC trigger efficiency of the light-by-light scattering in the ALICE experiment 2 / 15
ALICE experiment
Ultra peripheral collision
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Impact parameter is larger than twice the radius of nuclei b > R 1 + R 2
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Strong interaction is negligible
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Photon flux scales with Z 2 (Z Pb = 82)
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Light-by-Light scattering
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Calculations of cross-section at the LHC energies
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Has impact on
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Anomalous magnetic momentum (g − 2)
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New Physics
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Has been measured in the past at the LHC energies
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Unique low invariant mass region M γγ < 5 GeV /c 2 (in ALICE experiment)
M. Sharifi Kiasari, M.E. Kolobov (IFJ PAN) Studies of the UPC trigger efficiency of the light-by-light scattering in the ALICE experiment 4 / 15
Photon reconstruction in ALICE
Scheme of PCM Distribution of conversion
Triggers used in ALICE
Trigger - a certain situation in the detector, which starts data recording on the tapes.
Trigger elements:
For 2015:
0VBA = signal in V0A in BB window 0VBC = signal in V0C in BB window 0UBA = signal in ADA in BB window 0UBC = signal in ADC in BB window 0STP = SPD topological trigger
0SH1 = 0SM2 = 2 or more pixel or in outer SPD 0OMU = Between 2 and 6 TOF pad triggered 0OM2 = At least 2 TOF pads triggered For 2018:
0VBA = signal in V0A in BB window 0VBC = signal in V0C in BB window 0UBA = signal in ADA in BB window 0UBC = signal in ADC in BB window 0MLL = like sign dimuon low threshold 0STG = SPD topological trigger with optional opening angle
0SH1 = 0SM2 = 2 or more pixel or in outer SPD 0OMU = Between 2 and 6 TOF pad triggered 0OM2 = At least 2 TOF pads triggered
Trigger configuration:
For 2015:
CCUP2 (13) = *0VBA *0VBC 0OM2 0SM2 CCUP4 (14) = *0VBA *0VBC 0OMU 0SM2 CCUP9 (2)= *0VBA *0VBC *0UBA *0UBC 0STP CCUP8 (1) = *0VBA *0VBC *0UBA *0UBC 0STP 0OMU
CCUP10 (3) = *0VBA *0VBC *0UBA *0UBC 0SH1 CCUP11 (4) = *0UBA *0UBC 0STP 0OMU CCUP12 (5) = *0UBA *0UBC 0STP For 2018:
CCUP29-B-NOPF-CENTNOTRD (10) = *0VBA
*0VBC *0UBA *0UBC 0STG
CCUP30-B-NOPF-CENTNOTRD (11) = *0VBA
*0VBC *0UBA *0UBC 0STG 0OM2
CCUP31-B-NOPF-CENTNOTRD (12) = *0VBA
*0VBC *0UBA *0UBC 0STG 0OMU
For example, for trigger 17 in this nomenclature it would be: CCUP31-B-SPD2-CENTN OTRD = *0VBA *0VBC *0UBA *0UBC 0STG 0OMU.
For run in 2018 (Run2) parameters are a bit different (but the same nomenclature would be used).
M. Sharifi Kiasari, M.E. Kolobov (IFJ PAN) Studies of the UPC trigger efficiency of the light-by-light scattering in the ALICE experiment 6 / 15
Conversion radius of photon [cm] for different triggers
If we take a look at these histograms for different triggers, we will see how much the selection differs from one trigger to another:
Trigger 17 Trigger 12 Trigger 1
Trigger 10 Trigger 2
Peaks are coming from material where photons converted to e + e − pair.
ConvR0 vs ConvR1 for all photons and each configuration for Run2 (2018)
M. Sharifi Kiasari, M.E. Kolobov (IFJ PAN) Studies of the UPC trigger efficiency of the light-by-light scattering in the ALICE experiment 8 / 15
ConvR0 vs ConvR1 for all photons and each configuration
for Run1 (2015)
Fast Ors (trigger units of ITS SPD detector)
[0, 2] configuration [1, 1] configuration
[2, 0] configuration
M. Sharifi Kiasari, M.E. Kolobov (IFJ PAN) Studies of the UPC trigger efficiency of the light-by-light scattering in the ALICE experiment 10 / 15
Hits on the layer 0 and layer 1 of SPD of the tracks.
[0, 2] configuration [1, 1] configuration
[2, 0] configuration
2D Hists
Control plots, correlation between variables
M. Sharifi Kiasari, M.E. Kolobov (IFJ PAN) Studies of the UPC trigger efficiency of the light-by-light scattering in the ALICE experiment 12 / 15
Conclusion
To conclude we can say that as we saw from our analysis, the most efficient
trigger appeared to be number 17 - this was the main goal of our project. We’ve
also studied different photon configurations, have been familiarized with different
trigger types which are used for UPC in ALICE and gained some experience with
data analysis in ROOT. The results of this analysis can help us to understand
current triggering situation and will serve for future Run3 triggering scheme. They
can be used for future exclusions of beyond SM effects.
THANK YOU FOR YOUR ATTENTION!
M. Sharifi Kiasari, M.E. Kolobov (IFJ PAN) Studies of the UPC trigger efficiency of the light-by-light scattering in the ALICE experiment 14 / 15
Resourses
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Int. J. Mod. Phys. A 29 (2014) 1430044. e-Print: arXiv:1402.4476
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arXiv:1702.01625
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arXiv:1810.04602
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arXiv:1904.01243
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