On the Origin of Long-Lived Particles

TL;DR

The paper discusses how the proposed MATHUSLA detector can identify and analyze long-lived particles at the HL-LHC, providing insights into their origin and properties even without direct energy measurements.

Contribution

It introduces a simple, robust method for using MATHUSLA data to determine LLP production modes and underlying parameters, enhancing the potential for detailed physics characterization.

Findings

MATHUSLA can act as a trigger for CMS in LLP detection.

Combining MATHUSLA and CMS data allows mass and production mode determination with ~100 decays.

LLP and parent particle masses can be measured with less than 10% uncertainty.

Abstract

MATHUSLA is a proposed large-volume displaced vertex (DV) detector, situated on the surface above CMS and designed to search for long-lived particles (LLPs) produced at the HL-LHC. We show that a discovery of LLPs at MATHUSLA would not only prove the existence of BSM physics, it would also uncover the theoretical origin of the LLPs, despite the fact that MATHUSLA gathers no energy or momentum information on the LLP decay products. Our analysis is simple and robust, making it easily generalizable to include more complex LLP scenarios, and our methods are applicable to LLP decays discovered in ATLAS, CMS, LHCb, or other external detectors. In the event of an LLP detection, MATHUSLA can act as a Level-1 trigger for the main detector, guaranteeing that the LLP production event is read out at CMS. We perform an LLP simplified model analysis to show that combining information from the MATHUSLA and CMS detectors would allow the LLP production mode topology to be determined with as few as $\sim 100$ observed LLP decays. Underlying theory parameters, like the LLP and parent particle masses, can also be measured with $\lesssim 10\%$ precision. Together with information on the LLP decay mode from the geometric properties of the observed DV, it is clear that MATHUSLA and CMS together will be able to characterize any newly discovered physics in great detail.