Study of Muons in Ultra-High-Energy Cosmic-Ray Air Showers with the Telescope Array Experiment
- PDF / 622,153 Bytes
- 4 Pages / 612 x 792 pts (letter) Page_size
- 68 Downloads / 162 Views
ELEMENTARY PARTICLES AND FIELDS Experiment
Study of Muons in Ultra-High-Energy Cosmic-Ray Air Showers with the Telescope Array Experiment Y. Zhezher* (on behalf of the Telescope Array Collaboration) Institute for Nuclear Research, Russian Academy of Sciences, Moscow, 117312 Russia Received August 8, 2019; revised August 8, 2019; accepted August 8, 2019
Abstract—One of the uncertainties in the interpretation of ultra-high-energy cosmic-ray (UHECR) data comes from the high-energy hadronic interaction models used for air shower Monte-Carlo (MC) simulations. A long-standing problem of the so-called “muon excess”, the discrepancy of number of muons predicted by simulations and observed in the data, is believed to be caused by the incompleteness of modern hadronic interaction models, all of which are known to use the extrapolated values of the parameters of hadronic interactions, such as cross sections and multiplicities. The present work is dedicated to the study of muon densities in UHE extensive air showers from the Telescope Array experiment surface detector data. In the 7-year-data from the Telescope Array experiment, we find that the number of particles observed for signals with an expected muon purity of ∼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 QGSJETII-03 model for the proton-induced showers. A similar effect is also seen in comparison with other hadronic models such as QGSJETII-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 the larger lateral distances. DOI: 10.1134/S1063778819660517
I. INTRODUCTION The Telescope Array (TA) experiment is the largest ultra-high-energy (UHE) cosmic-ray experiment in the Northern Hemisphere, located near Delta, Utah, USA [1]. TA is designed to register the extensive air showers (EAS), cascades of secondary particles produced in the interactions of cosmic rays with energies greater than 1018 eV with the Earth’s atmosphere. In the Telescope Array, air showers are registered in two ways: particle density and the shower timing on the ground are measured with the surface detector (SD) array [2], while the fluorescence light from gas molecules in the atmosphere excited and ionized by the passage of EAS particles is detected with 38 fluorescence telescopes grouped into three fluorescence detector stations—Middle Drum, Black Rock Messa, and Long Ridge [3]. The simultaneous use of both surface detectors and fluorescence telescopes is known as the hybrid technique. The surface detector facility is an array of 507 plastic scintillator stations arranged on a square grid with 1.2 km spacing covering an approximate area of 700 km2 . Each detector is composed of two layers of *
E-mail: [email protected]
1.2-cm thick extruded scintillator of the 3 m2 effective area. UHECR data interpretation re
Data Loading...
