The current status of the GRAPES-3 extensive air shower experiment

Abstract

The GRAPES-3 is a dense extensive air shower array operating with ~400 scintillator detectors and it also contains a 560 m² tracking muon detector (E _μ>1GeV), at Ooty in India. 25% of scintillator detectors are instrumented with two fast photomultiplier tubes (PMTs) for extending the dynamic range to ~5×10³ particles m^-2. The scintillators, signal processing electronics and data recording systems were fabricated in-house to cut costs and optimize performance. The muon multiplicity distribution of the EAS is used to probe the composition of primary cosmic rays below the'knee', with an overlap with direct measurements. Search for multi-TeV γ-rays from point sources is done with the aid of the muon detector. A good angular resolution of 0.7° at 30 TeV, is measured from the shadow of the Moon on the isotropic flux of cosmic rays. A sensitive limit on the diffuse flux of 100 TeV γ-rays is placed by using muon detector to filter the charged cosmic ray background. A tracking muon detector allows sensitive measurements on coronal mass ejections and solar flares through Forbush decrease events. We have major expansion plans to enhance the sensitivity of the GRAPES-3 experiment in the areas listed above.