Paper proposal Study of High Muon Multiplicity cosmic events with - - PowerPoint PPT Presentation

Study of High Muon Multiplicity cosmic events with the ALICE- LHC

Mario Rodríguez Cahuantzi Physics Department – CINVESTAV (México)

Physics Forum, June 11th 2014

Paper proposal

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

• F 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.

Motivation of the analysis

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

• rder
• f

magnitude above the simulation)

Astroparticle Physics 19 (2003) 513–523

Astroparticle Physics 28 (2007) 273–286 DELPHI: ~18.5 days of data taking

The conclusion is similar to ALEPH: However, even the combination

• f

extreme assumptions

• f

highest measured flux value and pure iron spectrum fails to describe the abundance of high multiplicity events.

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.

ALICE collected 6 events with more than 100 atmospheric muons during 31.3 days of data taking.

Muon Multiplicity Distribution (MMD)

181 atm. muons 136 atm. muons 276 atm. muons 136 atm. muons 288 atm. muons

event display of muon bundles

Monte Carlo studies (MMD)

• Energy of the primary cosmic rays (PCR) that produces muon

bundles (# muons > 4) than can be detected by ALICE: 1014 < E < 1018 eV

• Energy of the PCR that produces HMM events (# muons > 100)

in ALICE: 1016 < E < 1018 eV

Knee Ankle

1 particle per m2 - second 1 particle per m2 - year 1 particle per km2 - year

Monte Carlo studies (MMD)

Monte Carlo studies (MMD)

MMD at intermediate multiplicity (7 < # muons < 40) for 27.2 days

• f data, compared with the fit for pure proton and Fe composition,
• Primary energy range of the simulation : 1014 < E < 1018 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.

MC with Absolute Normalization

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)

Corsika 6990 Corsika 7350 #run Fe (# of HMM) proton (# of HMM) Fe (# of HMM) proton (# 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

Statistical uncertainty

Corsika 6990 Corsika 7350 Fe proton Fe proton mean 42.2 23.6 60.8 31.4 sigma 5 (12%) 1.3 (5.5%) 3.5 (5.7%) 1.1 (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 each 8.6 days 1 event each 15.5 days 1 event each 6 days 1 event each 11.6 days

Rate [Hz]

1.3 x 10- 6 7.5 x 10- 7 1.9 x 10- 6 1 x 10-6

Stat. uncertainty (%)

12 6 6 4

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 each 8.6 days 1 event each 15.5 days 1 event each 6 days 1 event each 11.6 days

Rate [Hz]

1.3 x 10-6 7.5 x 10-7 1.9 x 10-6 1 x 10-6

Stat. uncertainty (%)

12 6 6 4

Syst. uncertainty (%)

10 11 19 7

Uncertainty (% syst. +

• stat. in

quadrature)

16 13 20 8

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 1016 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 x1016eV in which we found most of these events. This is compatible with a knee at about 3 x 1015 eV, or lower values, due to proton

• r very light elements and a spectral steepening of each element

depending on its charge.