Journal
PHYSICAL REVIEW D
Volume 98, Issue 2, Pages -Publisher
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevD.98.022002
Keywords
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Funding
- Japan Society for the Promotion of Science [JP21000002, JP19104006, JP15H05693, JP15H05741, JPH26707011]
- Institute for Cosmic Ray Research, The University of Tokyo
- U.S. National Science Foundation [PHY0601915, PHY-1404495, PHY-1404502, PHY-1607727]
- National Research Foundation of Korea [2017K I A4A3015188, 2016R1A2B4014967, 20 I7R1A2A1A05071429, 2016R1A5A1013277]
- Russian Academy of Sciences, RFBR Grant [I 6-02-00962a, 4.4502.13]
- Belgian Science Policy under IUAP (ULB) [VII/37]
- State of Utah
- University of Utah through the Office of the Vice President for Research
- Division Of Physics
- Direct For Mathematical & Physical Scien [1404495] Funding Source: National Science Foundation
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One of the uncertainties in the interpretation of ultrahigh energy cosmic ray data comes from the hadronic interaction models used for air shower Monte Carlo (MC) simulations. The number of muons observed at the ground from ultrahigh energy cosmic ray-induced air showers is expected to depend upon the hadronic interaction model. One may therefore test the hadronic interaction models by comparing the measured number of muons with the MC prediction. In this paper, we present the results of studies of muon densities in ultrahigh energy extensive air showers obtained by analyzing the signal of surface detector stations which should have high muon purity. The muon purity of a station will depend on both the inclination of the shower and the relative position of the station. In seven years' data from the Telescope Array experiment, we find that the number of particles observed for signals with an expected muon purity of similar to 65% at a lateral distance of 2000 m from the shower core is 1.72 +/- 0.10(stat) +/- 0.37(syst) times larger than the MC prediction value using the QGSJET II-03 model for proton-induced showers. A similar effect is also seen in comparisons with other hadronic models such as QGSJET II-04, which shows a 1.67 +/- 0.10 +/- 0.36 excess. We also studied the dependence of these excesses on lateral distances and found a slower decrease of the lateral distribution of muons in the data as compared to the MC, causing larger discrepancy at larger lateral distances.
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