Air-shower simulations with and without thinning: Artificial fluctuations and their suppression

The most common way to simplify extensive Monte Carlo simulations of air showers is to use the thinning approximation. We study its effect on the physical parameters reconstructed from simulated showers. To this end, we have created a library of showers simulated without thinning with energies from ${10}^{17}\mathrm{eV}$ to ${10}^{18}\mathrm{eV}$, various zenith angles, and primaries. This library is publicly available. Physically interesting applications of the showers simulated without thinning are discussed. Observables reconstructed from these showers are compared to those obtained with the thinning approximation. The amount of artificial fluctuations introduced by thinning is estimated. A simple method, multisampling, is suggested which results in a controllable suppression of artificial fluctuations and at the same time requires less demanding computational resources as compared to the usual thinning.