Enabling searches for long-lived particles at a future 10 TeV Muon Collider

TL;DR

The paper tackles detecting meta-stable charged particles at a future 10 TeV Muon Collider under significant beam-induced backgrounds. It uses a Gauge-MMSB SUSY benchmark with a long-lived stau and systematically studies hit-timing windows (Nominal, Medium, Loose) to assess how occupancy and track reconstruction affect LLP sensitivity. The key finding is that loosening timing acceptance can recover sensitivity up to $\sqrt{s}/2$ with substantial tracking efficiency and purity, along with concrete recommendations for tracker design and reconstruction improvements. This work informs detector concepts and LLP search strategies for next-generation muon colliders by highlighting timing-enabled LLP detection as a viable discovery channel.

Abstract

Muon Colliders offer fantastic opportunities to explore new phenomena at the energy frontier. However, beam-induced-backgrounds from muon decays pose significant challenges for detector design, readout, and reconstruction. Previous detector studies have employed stringent hit-timing requirements to reduce occupancy to manageable levels with negligible efficiency loss for prompt Standard Model particles. In the spirit of maximizing discovery potential, we investigate the capability of detecting meta-stable charged long-lived particles at a 10 TeV Muon Collider. As a benchmark, we consider a Gauge Mediated Supersymmetry Breaking (GMSB) model in which the stau is long-lived and can be identified as a high momentum, slowly moving track. We find that nominal hit-timing selections are too restrictive, and investigate the impact of looser requirements. We demonstrate that it is possible to recover sensitivity to particles with masses close to $\sqrt{s}/2$ by expanding time acceptance, and provide recommendations to further improve tracker design and track reconstruction.

Figures (13)

• Figure 1: Benchmark model. Pair-production of long-lived staus in a simplified GMSB SUSY model, with each stau decaying to a tau and gravitino.
• Figure 2: Kinematic properties of simulated staus including $p_T$ (top left), $\eta$ (top right), average $\beta\gamma$ (bottom left), and average $\beta$ (bottom right).
• Figure 3: The Tracker geometry from MuColl_v1, indicating the position of each layer in the $r{-}z$ plane towards-mucoll.
• Figure 4: Simulated arrival times of staus with mass $m$ = 1, 2.5, 3.5, and 4 TeV and BIB. Left to right: Vertex Barrel Layer 7, Inner Barrel Layer 2, Outer Barrel Layer 2.
• Figure 5: Hits per cm$^2$ (left) and occupancy (right) in the MuColl_v1 detector with 100$\%$ BIB for each hit-timing window considered.