Study of the γ/p discrimination at ∼100 TeV energy range with LHAASO experiment

Abstract The observation of high energy γ -rays is essential to unveil the long-standing enigma of the origin and acceleration of Galactic Cosmic Rays (CRs). Given its powerful capability of distinguishing between protons and γ -rays owing to its very large area of underground muon detectors, the LHAASO observatory will be the most sensitive ground-based detectors for γ -rays at 100 TeV with a CRs background rejection rate better than 10 − 5 . To evaluate the very small rejection rate with sufficient precision at energies above 100 TeV, one needs a large number of Monte Carlo events which is time consuming and challenging. As only the μ -poor events are interesting in the calculation of the rejection rate and take up a tiny fraction of the all CRs events, we modify the popular air shower simulation package, CORSIKA, by outputting only the μ -poor events for the following full detector simulation. As a result, our method is fully consistent with the evaluation made with the official CORSIKA at lower energy. Particularly, our improvement significantly escalate the calculation efficiency above 100 TeV, where it can be at least 50 times faster than using all events in simulation. By virtue of this new method, the γ /p discrimination of the LHAASO experiment at energies above 100 TeV is obtained for the first time, which indicates that LHAASO can reject CR backgrounds at a level of 10 − 5 and 10 − 9 at 100 TeV and 1 PeV respectively.