Depth of maximum of air-shower profiles: testing the compatibility of measurements performed at the Pierre Auger Observatory and the Telescope Array experiment

Alexey Yushkov,Jose Bellido,John Belz,Daisuke Ikeda,Vitor De Souza,Telescope Array Collaborations ,For The Pierre Auger ,William Hanlon,Michael Unger,Yoshiki Tsunesada,Pierre Sokolsky

doi:10.1051/epjconf/201921001009

Alexey Yushkov, Jose Bellido + Show 9 more

Open Access

https://doi.org/10.1051/epjconf/201921001009

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Abstract

At the Pierre Auger Observatory and the Telescope Array, the measurements of depths of maximum of airshower profiles, Xmax, are performed using direct observations of the longitudinal development of showers with the help of the fluorescence telescopes. Though the same detection technique is used at both installations, the straightforward comparison of the characteristics of the measured Xmax distributions is not possible due to the different approaches to the analysis of the recorded events. In this work, the Auger – Telescope Array composition working group presents a technique to compare the Xmax measurements from the Auger Observatory and the Telescope Array. Applying this technique the compatibility of the first two moments of the measured Xmax distributions is qualitatively tested for energies 1018.2 eV < E < 1019.0 eV using the recently published Telescope Array data from the Black Rock Mesa and Long Ridge fluorescence detector stations. For a quantitative comparison, simulations of air showers with EPOS-LHC, folded with effects of the Telescope Array detector, are required along with the inclusion in the analysis of the systematic uncertainties in the measurements of Xmax and the energies of the events.

Highlights

The large amount of data on the ultra-high-energy cosmic rays, collected by the Pierre Auger Observatory [1] operating in the Southern Hemisphere since 2004 and the Telescope Array (TA) [2] operating in the Northern Hemisphere since 2008, opens unprecedented possibilities for performing a comparison of the spectra, arrival directions and mass compositions of the cosmic rays coming from the complementary regions of the sky
In this paper we present a preliminary qualitative analysis of the compatibility of these TA measurements with the data of the Pierre Auger Observatory and outline the steps required for finalizing the comparison
While we could not identify any discrepancies beyond the statistical and systematic errors, more definite conclusions can be obtained after the shower simulations with EPOS-LHC for the TA Black Rock Mesa (BR)/Long Ridge (LR) will be available

Summary

Introduction

The large amount of data on the ultra-high-energy cosmic rays, collected by the Pierre Auger Observatory [1] operating in the Southern Hemisphere since 2004 and the Telescope Array (TA) [2] operating in the Northern Hemisphere since 2008, opens unprecedented possibilities for performing a comparison of the spectra, arrival directions and mass compositions of the cosmic rays coming from the complementary regions of the sky. From the Auger analysis, no fiducial field-of-view selection or corrections for the reconstruction and acceptance biases are applied to the TA data. Proton shapes of the measured Xmax distributions become compatible to the MC predictions for other pure primary compositions (helium, nitrogen) [6, 11]. From the comparison of Xmax measured by the TA BR/LR to the predictions of the QGSJetII-04 model (Fig. 3) and from the analysis of the shapes of Xmax distributions [6, 11], it follows that the data are compatible within the statistical and systematic errors to pure protons for all energies E > 1018.2 eV. Within systematic uncertainties, max of the data is in agreement with QGSJet II-04 protons and helium for most energy bins.

Statistical Hypothesis Tests

Discussion