Study of muon bundles from extensive air showers with the ALICE detector at CERN LHC

K Shtejer

doi:10.1088/1742-6596/718/5/052039

Abstract

ALICE is one of four large experiments at the CERN Large Hadron Collider, specially designed to study particle production in ultra-relativistic heavy-ion collisions. Located 52 meters underground with 28 meters of overburden rock, it has also been used to detect muons produced by cosmic-ray interactions in the upper atmosphere. The large size and excellent tracking capability of the ALICE Time Projection Chamber are exploited to study the muonic component of extensive air showers. We present the multiplicity distribution of these atmospheric muons and its comparison with Monte Carlo simulations. The latest version of the QGSJET hadronic interaction model was used to simulate the development of the resulting air showers. High multiplicity events containing more than 100 reconstructed muons were also studied. Similar events have been studied in previous underground experiments such as ALEPH and DELPHI at LEP without satisfactory explanations for the frequency of the highest multiplicity events. We demonstrate that the high muon-multiplicity events observed in ALICE stem from primary cosmic rays with energies above 1016 eV and that the frequency of these events can be successfully described by assuming a heavy mass composition of primary cosmic rays in this energy range.

Highlights

ALICE (A Large Ion Collider Experiment) [1], designed to study the Quark Gluon Plasma (QGP) in ultra-relativistic heavy-ion collisions at the CERN Large Hadron Collider (LHC) has been used to perform studies that are of relevance to astro-particle physics
The muons collected in ALICE are created in Extensive Air Showers (EAS) that develop after the interaction of primary cosmic rays with nuclei in the upper atmosphere
In this study we find that primaries with energy E > 1014 eV give rise to multi-muon events (Nμ > 4) reconstructed in the ALICE Time Projection Chamber (TPC)

Summary

Introduction

ALICE (A Large Ion Collider Experiment) [1], designed to study the Quark Gluon Plasma (QGP) in ultra-relativistic heavy-ion collisions at the CERN Large Hadron Collider (LHC) has been used to perform studies that are of relevance to astro-particle physics. In this study we find that primaries with energy E > 1014 eV give rise to multi-muon events (Nμ > 4) reconstructed in the ALICE Time Projection Chamber (TPC). Three additional detectors were used as triggers for this study: ACORDE (Alice COsmic Ray DEtector), TOF (Time Of Flight Detector) and SPD (Silicon Pixel detector). It is composed of two layers of silicon pixel modules centred upon the nominal interaction point of the LHC beams. The MMD obtained in ALICE is similar to the multiplicity distribution reported in the past by experiments at LEP, but those experiments did not provide any satisfactory explanation for the HMM events. The experimental rate of the HMM events is 1.9 × 10−6 Hz with a statistical uncertainty of 45%, giving an error in the rate of ±0.9 × 10−6 Hz

Number of muons

Systematic uncertainty

Findings

Conclusions