Revisiting LHC gluino mass bounds through radiative decays using MadAnalysis 5

Revisiting LHC gluino mass bounds through radiative decays using MadAnalysis 5



Revisiting LHC gluino mass bounds through radiative decays using MadAnalysis 5

Laboratoire Physique Subatomique et Cosmologie, Université Grenoble-Alpes,

CNRS/IN2P3, 53 rue des Martyrs, F-38026 Grenoble, France

The ATLAS and CMS experiments at the CERN LHC have collected about 25 of data each at the end of their 8 TeV run, and ruled out a huge swath of parameter space in the context of Minimally Supersymmetric Standard Model (MSSM). Limits on masses of the gluino () have been pushed to above 1 TeV. These limits are however extremely model dependent and do not always reflect the level of exclusion. So far the limits on the gluino mass using the simplified model approach only constrained its value using its three-body decays. We show in this work that already existing ATLAS and CMS analysis can also constrain the radiative gluino decay mode and we derived improved mass limits in particular when the mass difference between the LSP and the gluino is small.

1 Introduction and Motivation

Supersymmetry (SUSY) is one of the best motivated and most studied beyond Standard Model (BSM) paradigm. SUSY has an extremely rich phenomenology since it predicts a lot of new particles which could lie around the electroweak scale, which can be searched for at the LHC . In particular, the superpartners of the gluons, the gluinos , possess the largest pair-production cross section at the LHC and are therefore intensively searched for by experimental collaborations. Since no signal of SUSY has been uncovered, the only appropriate interpretation of these null searches was to set limits on the production cross section and masses of superpartners. However, interpreting the searches for NP is a non-trivial task and almost impossible to perform in a model independent way. The first focus of SUSY searches was to set limits on constrained Minimal Supersymmetric Standard Model (CMSSM) or minimal SUperGRAvity (mSUGRA) scenarios . The current lower limits on the gluino stand at, in the CMSSM, TeV for almost degenerate gluino and squarks. Nevertheless these limits are extremely model dependent and do not cover all possibilities in which a SUSY signal could show up. Indeed, if the lightest SUSY particle (LSP) is massive and degenerate with the squarks and/or gluinos, the so-called “compressed SUSY” scenarios, these limits can be seriously weakened. To relax some of these assumptions, the ATLAS and CMS collaborations have adopted the Simplified Model Spectra (SMS) approach (see for example  and references therein) to interpret the NP searches in a less model-dependent way.

Whether from the CMSSM/mSUGRA or the SMS interpretations of SUSY searches, if the first and second generation squarks are degenerate, the limits on their masses are quite strong and are pushed above the TeV scale. In this case, with light flavour squarks decoupled , then the two body decays are forbidden. In this situation, as far as the official experimental analyses are concerned, published gluino mass limits in the SMS approach focussed on its three-body decays or  , where are the lightest neutralino and chargino respectively. These decays are mediated by the squark corresponding to the flavour of the final states quarks, in the case where the couplings of the gluinos are flavour-symmetric.

Nevertheless, since the limits on the first and second generation pushed their masses beyond the TeV scale, the three-body decays may be heavily suppressed. Moreover, even in the case where the third generation squarks are allowed to be lighter, if the mass difference is small, then the three-body decays are kinematically suppressed and official analyses loose their sensitivity. However, there exists one decay mode which does not suffer from such suppression factors, which had received little attention so far: that of the two-body radiative decay .

2 The radiative gluino decay

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