Performance of LHAASO-WCDA and Observation of Crab Nebula as a Standard Candle

Understand

The first Water Cherenkov detector of the LHAASO experiment (WCDA-1) has been operating since April, 2019.

• The first 10 months of data have been analyzed to test its performance by observing the Crab Nebula as a standard candle.
• The WCDA-1 achieves the sensitivity of 65 mCU per year with a statistical threshold of 5 $\sigma$.
• In order to do so, 97.7\% cosmic ray background rejection rate around 1 TeV and 99.8\% around 6 TeV with an approximately photon acceptance about 50\% by using the $compactness$ of the shower footprints to be greater than 10 as the discriminator between gamma induced showers and the cosmic ray backgrounds.