100 TeV diffuse $$\gamma $$-rays observation by YangBaJing Hybrid Array

Abstract

Cosmic rays up to PeV energy are believed to be generated in our galaxy. $$\gamma $$ -rays at 100 TeV energies are important probe to identify PeVtrons. Besides, $$\gamma $$ -rays contain additional information on the propagation of the galactic cosmic rays. Diffuse $$\gamma $$ -rays originating from the Galactic plane from 20 to 200 TeV region are studied with early 160-day data collected by YangBaJing Hybrid Array (YBJ-HA), which is a hybrid array and consists of scintillation detectors and underground muon detectors. All-distance equi-zenith angle and time-swapping methods are used to analyze the number of $$\gamma $$ -rays excess. Because of no significant observation on $$\gamma $$ -ray emission, Helene’s method is adopted to derive the $$90\%$$ confidence level upper limits on the flux of diffuse galactic $$\gamma $$ -rays. And the limit to the ratio of the flux of $$\gamma $$ -rays to CRs is obtained at the order of $$10 ^{-4}$$ , which is the current best result at these energies.