When a Muon Is Not a Muon--- Detecting Fast Long-Lived Charged Particles from Cascade Decays Using a Mass Scan

TL;DR

This paper introduces a novel method using invariant mass distributions to detect fast long-lived charged particles, like sleptons, at the LHC, especially when traditional Time-of-Flight methods are ineffective.

Contribution

It proposes a mass scan technique analyzing invariant mass peaks to identify and measure long-lived sleptons and neutralino masses in collider experiments.

Findings

Effective detection of fast LLCPs demonstrated in simulations.

Method can measure both slepton and neutralino masses.

Applicable to models with boosted long-lived particles.

Abstract

If produced at the LHC, long-lived charged particles (LLCPs) would leave tracks in the muon detector. Time-of-Flight based methods for detecting these particles become less efficient if the LLCPs are fast, which would typically be the case if they are produced in the decays of some mother particle which is either heavy or very boosted. Thus for example, in supersymmetric models with long-lived sleptons, the long-lived sleptons produced in neutralino decays are often fast, with beta above 0.95 even at a 7 TeV LHC. We propose to use the (mis-measured) invariant mass distribution of "muon"-lepton pairs, where the "muon" could be a slepton LLCP, to detect it. This distribution peaks somewhat below the neutralino mass. The peak can be further enhanced by evaluating the distribution for different values of candidate "muon" masses. We simulate two GMSB-like models to show that this procedure can be used to detect the long-lived sleptons and measure both their mass and the neutralino mass.