The MATHUSLA Experiment

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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 .