Gravitino Dark Matter Scenarios with Massive Metastable Charged Sparticles at the LHC

TL;DR

Gravitino dark matter scenarios with a massive, metastable stau NLSP yield distinctive collider signatures via ToF and $dE/dx$. The authors use a fast ATLAS-like detector simulation, including tau momentum recalibration, to measure $m_{\tilde{\tau}_1}$ and to reconstruct cascade decays such as $\tilde{q}_R \to q\,\tilde{\chi}_1^0 \to q\,\tau\,\tilde{\tau}_1$ and $\tilde{q}_L \to q\,\tilde{\chi}_2^0 \to q \ell \tilde{\ell} \to q \ell\ell \tilde{\chi}_1^0 \to q \ell\ell\tau\tilde{\tau}_1$, extracting masses of $\tilde{\chi}_1^0$, $\tilde{\chi}_2^0$, $\tilde{q}_R$, $\tilde{q}_L$, $\tilde{\nu}_\tau$, and $\tilde{\ell}$ with sub-percent to few-percent precision (for the high-cross-section point $\epsilon$, and with lower precision for $\zeta,\eta$). The approach relies on imposing two metastable stau candidates, reconstructing tau momenta via transverse momentum balance, and applying invariant-mass selections to reveal resonance peaks; tau recalibration substantially improves resolution. The results indicate that LHC detectors can sensitively probe GDM scenarios at modest luminosities, offering a path to characterize the SUSY spectrum and test gravitino-related physics.

Abstract

We investigate the measurement of supersymmetric particle masses at the LHC in gravitino dark matter (GDM) scenarios where the next-to-lightest supersymmetric partner (NLSP) is the lighter scalar tau, or stau, and is stable on the scale of a detector. Such a massive metastable charged sparticle would have distinctive Time-of-Flight (ToF) and energy-loss ($dE/dx$) signatures. We summarise the documented accuracies expected to be achievable with the ATLAS detector in measurements of the stau mass and its momentum at the LHC. We then use a fast simulation of an LHC detector to demonstrate techniques for reconstructing the cascade decays of supersymmetric particles in GDM scenarios, using a parameterisation of the detector response to staus, taus and jets based on full simulation results. Supersymmetric pair-production events are selected with high redundancy and efficiency, and many valuable measurements can be made starting from stau tracks in the detector. We recalibrate the momenta of taus using transverse-momentum balance, and use kinematic cuts to select combinations of staus, taus, jets and leptons that exhibit peaks in invariant masses that correspond to various heavier sparticle species, with errors often comparable with the jet energy scale uncertainty.