Measurement of cosmic ray flux in the China JinPing underground laboratory

The China JinPing underground Laboratory （CJPL） is the deepest underground laboratory running in the world at present. In such a deep underground laboratory, the cosmic ray flux is a very important and necessary parameter for rare-event experiments. A plastic scintillator telescope system has been set up to measure the cosmic ray flux. The performance of the telescope system has been studied using the cosmic rays on the ground laboratory near the CJPL. Based on the underground experimental data taken from November 2010 to December 2011 in the CJPL, which has an effective live time of 171 days, the cosmic ray muon flux in the CJPL is measured to be （2.0±0.4）×10^-10/（cm2.s）. The ultra-low cosmic ray background guarantees an ideal environment for dark matter experiments at the CJPL.