TAUOLA update for decay channels with e+e− pairs in the final state

With the arrival of high luminosity B-factories like the Belle II experiment, τ decay measurements have become more precise than ever, allowing rarer processes to be explored, and finer details of τ decays to be studied. These are important to understand the spectrum of intermediate particles produced in τ decays. Therefore Monte Carlo generators, like the TAUOLA program, have to facilitate precision analysis as well as confront new models that constantly emerge with the availability of high statistics experimental data. New decay channels and models may lead to large variation of matrix elements size within the available phase space, as in the case when e+e- pairs are present in final state. It requires appropriate presampler of the phase space generator and a proper documentation to help users introduce their own models. While releasing a new update, it is important for the TAUOLA Monte Carlo library to maintain the general structure of the previous versions to preserve backward compatibility. The aim is to minimize changes from the user perspective. This paper presents a demonstration of new models implementation facilitated by the current update.

随着贝儿II实验（Belle II experiment）这类高亮度B工厂的问世，τ轻子衰变的测量精度已达到前所未有的水平，使得研究人员得以探索更为稀有的衰变过程，并对τ轻子衰变的精细细节展开深入研究。这些研究对于阐明τ轻子衰变过程中产生的中间粒子能谱具有重要意义。因此，诸如TAUOLA程序这类蒙特卡洛（Monte Carlo）生成器，不仅需要适配高精度分析的需求，还需应对伴随高统计量实验数据不断涌现的各类新型模型。当衰变末态存在正负电子对（e⁺e⁻ pairs）时，新的衰变道与模型可能会导致可用相空间内矩阵元的幅值出现大幅波动，这就要求相空间生成器配备适配的预采样机制，并提供完善的文档以辅助用户自定义自身的模型。在发布新版本更新时，TAUOLA蒙特卡洛库需保留既往版本的整体架构以维持向后兼容性，其目标是尽可能减少用户所需的修改量。本文展示了依托本次更新实现新型模型集成的具体实例。