How low can SUSY go? Matching, monojets and compressed spectra

TL;DR

This paper investigates the minimal mass limits for supersymmetric particles in compressed spectra scenarios at the LHC, emphasizing the importance of accurate initial state radiation modeling and uncertainties in setting these limits.

Contribution

It provides a detailed analysis of theoretical uncertainties in ISR modeling using matching schemes and derives updated mass limits for SUSY particles in compressed spectra scenarios.

Findings

Squark mass limit: >340 GeV

Gluino mass limit: >500 GeV

Degenerate squark and gluino limit: >650 GeV

Abstract

If supersymmetry (SUSY) has a compressed spectrum then the current mass limits from the LHC can be drastically reduced. We consider a possible 'worst case' scenario where the gluino and/or squarks are degenerate with the lightest SUSY particle (LSP). The most sensitive searches for these compressed spectra are via the final state LSPs recoiling against initial state radiation (ISR). Therefore it is vital that the ISR is understood and possible uncertainties in the predictions are evaluated. We use both MLM (with Pythia 6) and CKKW- L (with Pythia 8) matching and vary matching scales and parton shower properties to accurately determine the theoretical uncertainties in the kinematic distributions. All current LHC SUSY and monojet analyses are employed and we find the most constraining limits come from the CMS Razor and CMS monojet searches. For a scenario of squarks degenerate with the LSP and decoupled gluinos we find $M_{\tilde{q}}>340$ GeV. For gluinos degenerate with the LSP and decoupled squarks, $M_{\tilde{g}}>500$ GeV. For equal mass squarks and gluinos degenerate with the LSP, $M_{\tilde{q},\tilde{g}}>650$ GeV.