$$\gamma $$/hadron discrimination by analysis of the muon lateral distribution and the ALPAQUITA array

Abstract A new method using the muon lateral distribution and an underground muon detector to achieve high discrimination power against hadrons is presented. The method is designed to be applied in the Andes Large-area PArticle detector for Cosmic-ray physics and Astronomy (ALPACA) experiment in Bolivia. This new observatory in the Southern hemisphere has the goal of detecting &gt;100 TeV $$\gamma $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>γ</mml:mi> </mml:math> rays in search for the origins of Galactic cosmic rays. The method uses the weighted sum of the lateral distribution of the muons detected by underground detectors to separate between air showers initiated by cosmic rays and $$\gamma $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>γ</mml:mi> </mml:math> rays. We evaluate the performance of the method through Monte Carlo simulations with CORSIKA and Geant4 and apply the analysis to the prototype of ALPACA, ALPAQUITA. With the application of this method in ALPAQUITA, we achieve an improvement of about 18 % in the energy range from 60 to 100 TeV over the estimated sensitivity using only the total number of muons.