100 TeV diffuse γ-rays observation by YangBaJing Hybrid Array

Purpose 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.
Methods 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.
Result and conclusion 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.