标题： 在SHiNESS实验中寻找长寿命的轻中性微子和类轴子粒子 显示英文标题

标题： Searching for long-lived light neutralinos and axionlike particles at the SHiNESS experiment

摘要： 最近Soleti等人[JHEP03(2024)148]在即将建成的欧洲散裂中子源(ESS)设施上提出了一种新的实验称为SHiNESS，利用那里的2-GeV质子束流照射固定靶，以寻找可能处于不同质量范围并具有不同特征信号的隐藏纯中微子。此类特征信号包括电子-正电子对的过量，这些过量可能源自长寿命粒子(LLPs)的位移衰变。在ESS中，这类LLPs的主要来源是$\pi^+$介子和$\mu^+$轻子的静止衰变。我们选择研究R宇称破坏的超对称理论中长寿命轻中性微子的理论场景以及长寿命弱作用破坏的类轴子电荷粒子，因为这些LLPs可以从$\pi^+$和$\mu^+$的衰变中产生。由于$\pi^+$和$\mu^+$在ESS中静止衰变，我们计算了由此产生的LLPs的谱，从而估计了SHiNESS在这两种情景下对LLPs的预期灵敏度范围。我们的计算表明，在多个相关的基准情景中，SHiNESS只需几年的数据收集时间就可以探测到这些模型的大参数区域，超出现有的限制。 显示英文摘要

摘要： Recently Soleti et al. [JHEP03(2024)148] proposed a new experiment called SHiNESS at the upcoming European Spallation Source (ESS) facility, making use of the 2-GeV proton beam there impinging on a fixed target, in order to search for hidden sterile neutrinos that could lie in different mass ranges and arise with distinct signatures. Such signatures include excesses in electron-positron pairs that may originate from displaced decays of long-lived particles (LLPs). At the ESS, the dominant sources of such LLPs are decays at rest of $\pi^+$ mesons and $\mu^+$ leptons. We choose to investigate theoretical scenarios of long-lived light neutralinos in the R-parity-violating supersymmetry and long-lived weak-violating electrophilic axionlike particles, as these LLPs can be produced from decays of $\pi^+$ and $\mu^+$. Since the $\pi^+$'s and $\mu^+$'s decay at rest at the ESS, we compute the spectra of the therefrom produced LLPs, and thus estimate the expected sensitivity reach of SHiNESS to the LLPs in these two scenarios. Our calculation shows that in multiple relevant benchmark scenarios, SHiNESS can probe large parameter regions of these models beyond the existing bounds, in just a couple of years of data-collection time.