Hunting for neutral, long-lived exotica at the LHC using a missing transverse energy signature

TL;DR

This paper explores using missing transverse energy signatures at the LHC to detect neutral, long-lived particles that decay outside the detector, extending search capabilities beyond traditional displaced particle methods.

Contribution

It introduces a model-independent method using $E_T^{miss}$ signals to set limits on long-lived particles, applicable across various models and decay channels.

Findings

Set 95% CL upper limits on production cross sections for specific long-lived particle models.

Demonstrated that $E_T^{miss}$ searches can match displaced particle searches for decay distances over a few meters.

Provided a comprehensive grid of limits for particle and mediator masses up to 2 TeV.

Abstract

Searches at the Large Hadron Collider (LHC) for neutral, long-lived particles have historically relied on the detection of displaced particles produced by their decay $\textit{within}$ the detector volume. In this paper we study the potential of the complementary signature comprising of the missing transverse energy ($E_T^{miss}$) signal, traditionally used to look for dark matter, e.g., the lightest supersymmetric particle (LSP), to extend the LHC coverage to models with long-lived (LL) particles when they decay $\textit{outside}$ the detector. Using CMS and ATLAS analyses at the 8 TeV LHC, we set an upper limit at the 95% confidence level (CL) on the production cross sections for two specific scenarios: (i) a model with a heavy non-standard model Higgs boson decaying to a LL scalar and (ii) an R-parity violating RPV SUSY model with a LL neutralino. We show that this method can significantly extend the LHC sensitivity to neutral, LL particles with arbitrary large lifetimes and that the limits obtained from a $E_T^{miss}$ signal are comparable to those from displaced particle searches for decay distances above a few meters. Results obtained in this study do not not depend on the specific decay channel of the LL particle and therefore are model-independent in this sense. We provide limits for the whole two-dimensional plane in terms of the mass of the LL particle and the mass of the mediator up to masses of 2 TeV including particular benchmarks studied in the original experimental papers. We have made these limits available in the form of a grid which can be used for the interpretation of various other new physics models.