Improvements in charged lepton and photon propagation for the software PROPOSAL

Accurate particle simulations are essential for the next generation of experiments in astroparticle physics. The Monte Carlo simulation library PROPOSAL is a flexible tool to efficiently propagate high-energy leptons and photons through large volumes of media, for example in the context of underground observatories. It is written as a C++ library, including a Python interface. In this paper, the most recent updates of PROPOSAL are described, including the addition of electron, positron, and photon propagation, for which new interaction types have been implemented. This allows the usage of PROPOSAL to simulate electromagnetic particle cascades, for example in the context of air shower simulations. The precision of the propagation has been improved by including rare interaction processes, new photonuclear parametrizations, deflections in stochastic interactions, and the possibility of propagating in inhomogeneous density distributions. Additional technical improvements regarding the interpolation routine and the propagation algorithm are described.

精确的粒子模拟对于下一代粒子天体物理学（astroparticle physics）实验至关重要。蒙特卡洛（Monte Carlo）模拟库PROPOSAL是一款灵活的工具，可高效地将高能轻子与光子传播穿过大体积介质，例如应用于地下观测站的相关场景中。该库以C++语言编写，并附带Python接口。本文详细介绍了PROPOSAL的最新更新内容，其中新增了电子、正电子与光子的传播功能，并为其实现了全新的相互作用类型。这使得PROPOSAL能够用于模拟电磁粒子级联过程，例如在空气簇射模拟的场景中。通过纳入稀有相互作用过程、全新的光核参数化方案、随机相互作用中的偏转效应，以及支持在非均匀密度分布介质中进行传播，该工具的传播精度得到了显著提升。此外，本文还阐述了插值程序与传播算法方面的多项技术优化。