The MATHUSLA Experiment

超越标准模型的长寿命粒子(LLP)在许多新的物理扩展中被激发，并可能与暗物质、等级问题、中微子质量和重子不对称有关。基于对撞机的粒子物理实验正越来越多地将精力集中在搜索非瞬时衰变的特征上，但现有搜索的范围本质上受到探测器的物理尺寸和碰撞相互作用点附近的限制。MATHUSLA实验是一个拟议的LLP探测器，将在欧洲核子研究中心实验室建造，用于在大约2027年开始的高光度LHC期间运行。对于各种动机良好的模型，例如从标准模型类希格斯产生的强子衰变LLP，预期的MATHUSLA灵敏度比LHC主探测器(ATLAS和CMS)的灵敏度提高了一到两个数量级。探测器将由一个大的(100m X 100m X 25m)充满空气的衰变体积组成，位于CMS相互作用区上方的表面上，距离CMS作用区约100米。MATHUSLA本身是以模块化方式设计的，因此探测器可以分阶段建造。每个10M x 10M模块都将配备多层塑料闪烁体，由硅光电倍增管通过波长移动光纤读出。这些层位于衰变体积的顶部和底部，能够从大型强子对撞机的高能质子-质子碰撞产生的LLP衰变中重建带电粒子的轨迹。可通过一层或多层电阻板室提供额外的精确跟踪。通过从衰变子体重建LLP的衰变顶点，并利用闪烁体的计时信息，LLP衰变顶点可以重构并与宇宙射线或大型强子对撞机穿透标准模型粒子的背景区分开来。MATHUSLA将能够探测和解析具有从GeV尺度到弱或TeV尺度的质量的LLP的衰变顶点，并且寿命接近大爆炸核合成施加的约0.01 S的上限。此外，在发现LLP的情况下，对MATHUSLA和CMS数据的联合分析可以确定LLP的产生模式和衰变模式，以及LLP和母粒质量。加拿大MATHUSLA小组目前由三所加拿大大学(维多利亚大学、多伦多大学和麦吉尔大学)的四名教职员工组成。这项提案是为资助和扩大正在进行的与MATHUSLA实验相关的研究而提出的第一个项目赠款请求。

Long lived particles (LLPs) beyond the Standard Model are motivated in many new physics extensions, and may have connections to dark matter, the hierarchy problem, neutrino masses, and baryon asymmetry. Collider-based particle physics experiments are increasingly focusing effort on searches for signatures of non-prompt decays, but the scope of the existing searches is intrinsically limited by the physical size of the detectors and proximity to the collision interaction point. The MATHUSLA experiment is a proposed detector of LLPs to be constructed at the CERN laboratory for operation during the high luminosity LHC period, beginning in approximately 2027. The expected MATHUSLA sensitivity for various well-motivated models, such as hadronically decaying LLPs produced from a Standard Model-like Higgs, improves upon that of the LHC main detectors (ATLAS and CMS) by as much as one or two orders of magnitude. The detector will consist of a large (100m x 100m x 25m), air-filled decay volume located on the surface above, and approximately 100m distant from, the CMS interaction region. MATHUSLA itself is designed in a modular fashion, such that the detector can be built in a staged manner. Each 10m x 10m module will be instrumented with layers of plastic scintillators that are read out by silicon photomultipliers via wavelength-shifting optical fibres. These layers, located at the top and bottom of the decay volume, enable the reconstruction of the trajectories of charged particles from the decays of LLPs produced in the high energy proton-proton collisions of the LHC. Additional precision tracking may be provided by one or more layers of resistive plate chambers. By reconstructing the decay vertex of the LLPs from the decay daughters and exploiting timing information from the scintillators, LLP decay vertices can be reconstructed and distinguished from backgrounds from cosmic rays or penetrating Standard Model particles from the LHC. MATHUSLA will be able to detect and resolve decay vertices from LLPs with masses from the GeV scale all the way up to the weak or TeV scale, and with lifetimes approaching the upper limit of ~0.01 s imposed by Big Bang Nucleosynthesis. Furthermore, in the event of an LLP discovery, a combined analysis of MATHUSLA and CMS data could determine the LLP production mode and decay mode, as well as the LLP and parent particle masses. The Canadian MATHUSLA group currently consists of four faculty members at three Canadian universities (University of Victoria, University of Toronto, and McGill University). This proposal is a first project grant request to fund and expand ongoing research related to the MATHUSLA experiment .