Hunting wino and higgsino dark matter at the muon collider with disappearing tracks

TL;DR

This paper explores the potential of a 10 TeV muon collider to detect long-lived charged particles indicative of wino and higgsino dark matter, using a novel background suppression strategy for disappearing tracks.

Contribution

It introduces a hit-level selection method exploiting timing and hit correlations to effectively suppress muon beam-induced backgrounds in disappearing track searches.

Findings

Muon collider can probe wino and higgsino masses close to half the center-of-mass energy.

The background from beam-induced decays can be reduced to 0.08 tracks per event.

The analysis demonstrates competitive sensitivity to dark matter candidates with a 10 TeV muon collider.

Abstract

We study the capabilities of a muon collider experiment to detect disappearing tracks originating when a heavy and electrically charged long-lived particle decays via $X^+ \to Y^+ Z^0$, where $X^+$ and $Z^0$ are two almost mass degenerate new states and $Y^+$ is a charged Standard Model particle. The backgrounds induced by the in-flight decays of the muon beams (BIB) can create detector hit combinations that mimic long-lived particle signatures, making the search a daunting task. We design a simple strategy to tame the BIB, based on a detector-hit-level selection exploiting timing information and hit-to-hit correlations, followed by simple requirements on the quality of reconstructed tracks. Our strategy allows us to reduce the number of tracks from BIB to an average of 0.08 per event, hence being able to design a cut-and-count analysis that shows that it is possible to cover weak doublets and triplets with masses close to $\sqrt{s}/2$ in the 0.1-10 ns range. In particular, this implies that a 10 TeV muon collider is able to probe thermal MSSM higgsinos and thermal MSSM winos, thus rivaling the FCC-hh in that respect, and further enlarging the physics program of the muon collider into the territory of WIMP dark matter and long-lived signatures. We also provide parton-to-reconstructed level efficiency maps, allowing an estimation of the coverage of disappearing tracks at muon colliders for arbitrary models.