Conciliating SUSY with the Z-peaked excess

Vasiliki A Mitsou

doi:10.1051/epjconf/201612602021

Abstract

The ATLAS experiment observed an excess at the $3\sigma$ level in the channel of $Z$ boson, jets and high missing transverse momentum in the full 2012 dataset at 8 TeV while searching for SUSY. The question arises whether the abundance and the kinematical features of this excess are compatible with the yet unconstrained supersymmetric realm, respecting at the same time the measured Higgs boson properties and dark matter density. By trying to explain this signal with SUSY we find that only relatively light gluinos together with a heavy neutralino NLSP decaying predominantly to a $Z$ boson plus a light gravitino could reproduce the excess. We construct an explicit general gauge mediation model able to match the observed signal. More sophisticated models could also reproduce the signal, as long as it features light gluinos, or heavy particles with a strong production cross section, producing at least one $Z$ boson in its decay chain. The implications of our findings for the Run II at LHC with the scaling on the $Z$ peak, as well as for the direct search of gluinos and other SUSY particles, are also discussed.

Highlights

Supersymmetry (SUSY) [1] is an extension of the Standard Model (SM) that assigns to each SM field a superpartner with a spin differing by half a unit
Z bosons are produced through the decay chains of most Minimal Supersymmetric Standard Model (MSSM) particles, the multiplicity obtained per each supersymmetric particle depends on the identity of the supersymmetric particle initially produced and on the supersymmetric spectrum below its mass
As we have shown in the previous sections, the excess observed in ATLAS, if due to SUSY, requires a gluino of a mass ∼ 1 TeV producing nearly one Z boson per gluino in its decay

Summary

Introduction

Supersymmetry (SUSY) [1] is an extension of the Standard Model (SM) that assigns to each SM field a superpartner with a spin differing by half a unit. SUSY solves in an elegant manner several open issues of the SM, such as the hierarchy problem, the nature of dark matter [2], and the grand unification It is one of the most relevant scenarios of new physics explored at the LHC, no clear signs of SUSY have been observed so far. The observed signal can only be explained if one has a large production cross section of heavy SUSY particles (gluinos or squarks) whose decay chain contains about one Z boson per parent particle If such an explanation is the answer to the observed excess, our study points out the way to confirm it in the Run II of LHC, as well as cosmological implications, in particular the particle content of dark matter in the Universe. The resulting scheme of SUSY particle mass hierarchy, including charginos and neutralinos, will be apparent

Z-boson production in the MSSM

Decay of sparticles to Z bosons

A possible explanation in General Gauge Mediation

Prospects for SUSY at LHC13

Findings

Conclusions