The Muon Detector Study For AS γ Experiment In Tibet

In order to exclude the cosmic ray background and increase the sensitivity of observing y rays, we proposed the underground muon detector experiment, which is an upgrade experiment of Tibet ASy array. In2010, Chinese group had completed the infrastructure of MDA (one of12water Cherenkov muon detectors), which has16small detector units. In2011, two small detector units of MDA were installed and operated successfully. The main work I have done is presented as follows:(1) For the muon detector using water Cerenkov technique, keeping the long-term stability of water is one of the key issues. In order to stabilize the water quality and increase the reflectivity of the Cherenkov photons in the pool, the large Tyvek bag was developed.(2) To study the performance of the20-inch photomultiplier tube R3600.(3) To install and run the detector in Tibet experiment site. A single muon peak was clearly observed with approximately300photoelectrons in each small detector unit, which meets the requirements of the physics goals. Both self-trigger mode and using the L3C scintillator signal as the trigger were carried out to test the performance of the small detector unit. The result shows that the resolution of the single muon is about30%, which is better than that observed with2007prototype detector. Moreover, the position non-uniformity of the pool was investigated. The obtained non-uniformity is better than6%.(4) In order to fully understand the experimental results, the detector simulation was done by using the geant4code. The simulation results show that the number of the photoelectrons collected by PMT is consistent with which of the experimental data.