Probing conversion-driven freeze-out at the LHC

TL;DR

This paper investigates how conversion-driven freeze-out, a dark matter production mechanism, can be tested at the LHC through various search strategies for long-lived particles, highlighting current constraints and potential improvements.

Contribution

It provides a comprehensive analysis of LHC search strategies for conversion-driven freeze-out, including novel modifications to displaced vertex searches to enhance sensitivity.

Findings

Current LHC searches constrain parts of the parameter space.

Displaced vertex analysis can be significantly improved with minor modifications.

Complementarity of different search strategies covers the entire lifetime range.

Abstract

Conversion-driven freeze-out is an appealing mechanism to explain the observed relic density while naturally accommodating the null-results from direct and indirect detection due to a very weak dark matter coupling. Interestingly, the scenario predicts long-lived particles decaying into dark matter with lifetimes favorably coinciding with the range that can be resolved at the LHC. However, the small mass splitting between the long-lived particle and dark matter renders the visible decay products soft, challenging current search strategies. We consider four different classes of searches covering the entire range of lifetimes: heavy stable charge particles, disappearing tracks, displaced vertices, and missing energy searches. We discuss the applicability of these searches to conversion-driven freeze-out and derive current constraints highlighting their complementarity. For the displaced vertices search, we demonstrate how a slight modification of the current analysis significantly improves its sensitivity to the scenario.