Paper proposal Study of High Muon Multiplicity cosmic events with the ALICE- LHC Mario Rodríguez Cahuantzi Physics Department – CINVESTAV (México) Physics Forum, June 11th 2014
Outline Motivation of the analysis Analysis of data Monte Carlo studies Summary
Motivation of the analysis ALEPH: 140 m of rock, momentum muon threshold p > 70/cosθ underground scintillators, HCAL (horizontal area ~ 50 m2 ), TPC projected area ~ 16 m2 DELPHI: 100 m of rock, momentum muon threshold p > 52/cosθ Hadron calorimeter (horizontal area ~ 75 m2), muon barrel, TPC, T oF and outer detectors L3+C: 30 m of rock, momentum muon threshold p > 20/cosθ + surface array Scintillator surface array (200 m2), trigger, muon barrel (100 m2), hadron calorimeter, etc.
The conclusion is similar to Motivation of the analysis ALEPH: Astroparticle Physics 19 (2003) 513–523 However, even the combination of extreme assumptions of highest measured flux value and pure iron spectrum fails to describe the abundance of high multiplicity events. Astroparticle Physics 28 (2007) 273–286 DELPHI: ~18.5 days of data taking ALEPH: ~20 days of data taking Data indicate that heavier component is needed to explain higher multiplicity muon bundles These muon bundles are not well described (almost an order of magnitude above the simulation)
Analysis of data (run selection) Between the years 2010 and 2013, ALICE collected several millions of events during the cosmic data taking sessions. The run selection took into account the relevant system for cosmic ray studies: ACORDE, SPD and TOF as trigger detectors and the TPC as readout. The total sample corresponds to 31.3 days of data taking.
Muon Multiplicity Distribution (MMD) ALICE collected 6 events with more than 100 atmospheric muons during 31.3 days of data taking.
event display of muon bundles 276 atm. muons 136 atm. muons 181 atm. muons 136 atm. muons 288 atm. muons
Monte Carlo studies (MMD) Knee Ankle 1 particle per m2 - second 1 particle per m2 - year 1 particle per km2 - year • Energy of the primary cosmic rays (PCR) that produces muon bundles (# muons > 4) than can be detected by ALICE: 10 14 < E < 10 18 eV • Energy of the PCR that produces HMM events (# muons > 100) in ALICE: 10 16 < E < 10 18 eV
Monte Carlo studies (MMD)
Monte Carlo studies (MMD) MMD at intermediate multiplicity (7 < # muons < 40) for 27.2 days of data, compared with the fit for pure proton and Fe composition, MC with Absolute Normalization • Primary energy range of the simulation : 10 14 < E < 10 18 eV • The data are, as expected, in between the pure proton composition (light elements) and pure Fe (heavy elements). • The lower multiplicities (lower primary energies) are closer to pure Proton as expected.
Monte Carlo studies : High Muon Multiplicity (HMM) events DATA: 5 EVENTS IN 31.3 DAYS 1 event each 6.3 days rate: 1.8 x 10 -6 Hz (uncert. ~40%) We want to see how is the rate of HMM events (Nmu>100) with the simulation for pure proton and pure Fe samples. We simulate 365 days of effective time to reduce the fluctuations. Then we count how many events with Nmu>100 (HMM events) we have for both the samples. To reduce it we did it 5 times (run 1 → 365 days, run 2 → 365, …, run 5 → 365)
Monte Carlo studies : High Muon Multiplicity (HMM) events DATA: 5 EVENTS IN 31.3 DAYS 1 event each 6.3 days rate: 1.8 x 10 -6 Hz (uncert. ~40%) We want to see how is the rate of HMM events (Nmu>100) with the simulation for pure proton and pure Fe samples. We simulate 365 days of effective time to reduce the fluctuations. Then we count how many events with Nmu>100 (HMM events) we have for both the samples. To reduce it we did it 5 times (run 1 → 365 days, run 2 → 365, …, run 5 → 365)
Monte Carlo studies (HMM) Statistical uncertainty Corsika 6990 Corsika 7350 #run Fe proton Fe proton (# of HMM) (# of HMM) (# of HMM) (# of HMM) 1 51 27 52 30 2 42 24 71 32 3 31 25 62 29 4 34 20 61 35 5 53 22 58 31 Corsika 6990 Corsika 7350 Fe proton Fe proton mean 42.2 23.6 60.8 31.4 sigma 5 (12%) 1.3 3.5 1.1 (5.5%) (5.7%) (3.7%)
Monte Carlo studies (HMM) Statistical uncertainty QGSJET II-03 QGSJET II-04 Fe proton Fe proton # of HMM 42.2 23.6 60.8 31.4 Rate / days 1 event 1 event 1 event 1 event each 8.6 each 15.5 each 6 each 11.6 days days days days Rate [Hz] 1.3 x 10- 7.5 x 10- 1.9 x 10- 1 x 10-6 6 7 6 Stat. 12 6 6 4 uncertainty (%)
Final Results (HMM) QGSJET II-03 QGSJET II-04 Fe proton Fe proton # of HMM 42.2 23.6 60.8 31.4 Rate / days 1 event 1 event 1 event 1 event each 8.6 each 15.5 each 6 each 11.6 days days days days Rate [Hz] 1.3 x 10-6 7.5 x 10-7 1.9 x 10-6 1 x 10-6 Stat. 12 6 6 4 uncertainty (%) Syst. 10 11 19 7 uncertainty (%) Uncertainty 16 13 20 8 (% syst. + stat. in quadrature) DATA: 5 EVENTS IN 31.3 DAYS 1 event each 6.3 days rate: 1.8 x 10-6 Hz (uncert. ~40%)
Summary: Message of the paper In the period 2010-2013 the ALICE experiment took more than 31 effective days of dedicated cosmic runs. Thi result on the muon multiplicity distribution, obtained with an absolute normalization of the simulated data, confirms the reliability of cosmic data taking and its explanation with simulation programs, allowing us to face the study of HMM events. These events, already detected in the past from some LEP experiments like ALEPH and DELPHI, and actually without any explanation, have been recorded also in ALICE. ALICE is able to reproduce with the simulation the rate of HMM events and indicate that they are mostly due to primary cosmic rays of heavy nuclei with an energy above 10 16 eV, and a shower core located near ALICE . This is in agreement with an heavier primary composition above the energy of the knee. In particular, the rate of the pure Fe composition is so close to the data to suggest an heavy composition above the energy 3 x10 16 eV in which we found most of these events. This is compatible with a knee at about 3 x 10 15 eV, or lower values, due to proton or very light elements and a spectral steepening of each element depending on its charge.
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