Probing Dark Matter freeze-in with long-lived particle signatures: MATHUSLA, HL-LHC and FCC-hh

TL;DR

This paper explores how collider experiments like MATHUSLA, HL-LHC, and FCC-hh can detect long-lived particles to probe Dark Matter freeze-in scenarios, analyzing sensitivities, constraints, and technical factors affecting relic abundance.

Contribution

It provides a comprehensive analysis of collider sensitivities for Dark Matter freeze-in via long-lived particles, including the impact of future detectors and collider energies, with detailed theoretical considerations.

Findings

MATHUSLA can significantly extend the sensitivity to freeze-in Dark Matter.

Future 100 TeV colliders improve detection prospects for long-lived particles.

Thermal masses and scattering processes critically influence relic abundance calculations.

Abstract

Collider searches for long-lived particles yield a promising avenue to probe the freeze-in production of Dark Matter via the decay of a parent particle. We analyze the prospects of probing the parameter space of Dark Matter freeze-in from the decay of neutral parent particles at the LHC and beyond, taking as a case study a freeze-in Dark Matter scenario via the Standard Model Higgs. We obtain the projected sensitivity of the proposed MATHUSLA surface detector (for MATHUSLA100 and MATHUSLA200 configurations) for long-lived particle searches to the freeze-in Dark Matter parameter space, and study its complementarity to searches by ATLAS and CMS at HL-LHC, as well as the interplay with constraints from Cosmology: Big-Bang Nucleosynthesis and Lyman-$\alpha$ forest observations. We then analyze the improvement in sensitivity that would come from a forward detector within a future 100 TeV $pp$-collider. In addition, we discuss several technical aspects of the present Dark Matter freeze-in scenario: the role of the electroweak phase transition; the inclusion of thermal masses, which have been previously disregarded in freeze-in from decay studies; the impact of $2\to 2$ scattering processes on the Dark Matter relic abundance; and the interplay between freeze-in and super-WIMP Dark Matter production mechanisms.