Effects of Thunderstorm Electric Field on the Lateral Distribution of Cosmic Ray Secondary Particles at LHAASO

The charged components of cosmic ray secondary particles are deflected by thunderstorm electric fields as they pass through kilometer-scale thunderclouds. As a result, the information on location of secondary particles reaching the observation level will be affected, and the lateral distribution will also be changed. In this paper, the Monte Carlo method is used to simulate the effects of near-earth thunderstorm electric field on the lateral distribution of secondary particles at LHAASO. A vertical and uniform atmospheric electric field model is used in our simulations. The results show that during thunderstorm the lateral distribution of secondary particles widens, and the variation amplitude is not only associated with the strength of electric field, but also dependent upon the primary energy and zenith angle of cosmic rays. In an electric field of - 1000 V$·$cm${}^{-1}$ (below the threshold of the Relatively Runaway Electron Avalanche, RREA), the variation amplitude of the lateral distribution of secondary particles is about 0.7% for $\theta =$ 0${}^{\circ }$, and the variation amplitude reaches 4.7% for $\theta =$ 50${}^{\circ }$. The primary energy of cosmic rays is about 180 GeV, the increasing amplitude is about 0.6%. When the primary energy is about 560 TeV, the variation can be up to 20.1%. In an electric field of - 1700 V$·$cm${}^{-1}$ (above the threshold of the RREA process), the increasing amplitude of the lateral distribution is greater than that in an electric field of - 1000 V$·$ cm${}^{-1}$. And the variation amplitude is 3.8% for $\theta =$ 0${}^{\circ }$ and 34% for $\theta =$ 50${}^{\circ }$, respectively. For the primary energy of about 180 GeV, the increasing amplitude of secondary particles is 9.9%. For the primary energy of about 560 TeV, the variation can be as high as 119%. Our simulation results are helpful to understand the deflection mechanisms of cosmic ray secondary particles generated by the near-earth thunderstorm electric field, as well as the variation of LHAASO data during thunderstorms.