WimPyDD: An object–oriented Python code for the calculation of WIMP direct detection signals

We introduce WimPyDD, a modular, object–oriented and customizable Python code that calculates accurate predictions of nuclear scattering expected rates for Weakly Interacting Massive Particle (WIMP) direct–detection experiments within the framework of Galilean–invariant non–relativistic effective theory in virtually any scenario, including inelastic scattering, an arbitrary WIMP spin and a generic WIMP velocity distribution in the Galactic halo. WimPyDD can also be used to analyze WIMP direct detection signals in halo–independent approaches where the velocity distribution is written in terms of a superposition of streams taken as free parameters. WimPyDD exploits the factorization of the three main components that enter in the calculation of direct detection signals: i) the Wilson coefficients that encode the dependence of the signals on the ultraviolet completion of the effective theory; ii) a response function that depends on the nuclear physics and on the main features of the experimental detector (acceptance, energy resolution, response to nuclear recoils); iii) a halo function that depends on the WIMP velocity distribution and that encodes the astrophysical inputs. In WimPyDD these three components are calculated and stored separately for later interpolation and combined together only as the last step of the signal evaluation procedure. This makes the phenomenological study of the direct detection scattering rate with WimPyDD transparent and fast also when the parameter space of the WIMP model has a large dimensionality.

我们提出了WimPyDD：一款模块化、面向对象且可定制的Python代码，可在伽利略不变非相对论有效理论框架下，精准计算弱相互作用大质量粒子（Weakly Interacting Massive Particle，WIMP）直接探测实验的核散射预期反应率，覆盖几乎所有可能的场景，包括非弹性散射、任意WIMP自旋以及银晕中通用的WIMP速度分布。WimPyDD还可用于采用晕独立方法分析WIMP直接探测信号，此类方法中将速度分布表示为若干作为自由参数的流的叠加。WimPyDD对直接探测信号计算所需的三大核心组分进行了因式分解：其一为威尔逊系数（Wilson coefficients），用于表征信号对有效理论紫外完备性的依赖；其二为响应函数，其取决于核物理性质以及实验探测器的关键特性（如接受度、能量分辨率、对核反冲的响应）；其三为晕函数，其取决于WIMP速度分布并编码天体物理输入信息。在WimPyDD中，这三大组分将被分别计算并存储，以供后续插值调用，仅在信号评估流程的最后一步才将三者结合。这一设计使得利用WimPyDD开展直接探测散射率的现象学研究既清晰透明又高效快捷，即便WIMP模型的参数空间维度较高时亦是如此。