METing SUSY on the Z peak

TL;DR

This paper proposes a SUSY-based explanation for the ATLAS Z-peak excess, suggesting light gluinos and heavy neutralinos decaying to Z-bosons could account for the observed signal.

Contribution

It introduces a specific SUSY model with light gluinos and heavy neutralinos that can reproduce the ATLAS excess while satisfying experimental constraints.

Findings

Light gluinos with mass less than 1.2 TeV are compatible with the excess.

Heavy neutralino NLSP around 400 GeV decays predominantly to Z-boson and gravitino.

The model can explain the excess without conflicting with existing limits.

Abstract

Recently the ATLAS experiment announced a 3 $\sigma$ excess at the Z-peak consisting of 29 pairs of leptons together with two or more jets, $E_T^{\rm miss}> 225$ GeV and $H_T \geq 600$ GeV, to be compared with $10.6 \pm 3.2$ expected lepton pairs in the Standard Model. No excess outside the Z-peak was observed. By trying to explain this signal with SUSY we find that only relatively light gluinos, $m_{\tilde g} \lesssim 1.2$ TeV, together with a heavy neutralino NLSP of $m_{\tilde \chi} \gtrsim 400$ GeV decaying predominantly to Z-boson plus a light gravitino, such that nearly every gluino produces at least one Z-boson in its decay chain, could reproduce the excess. We construct an explicit general gauge mediation model able to reproduce the observed signal overcoming all the experimental limits. Needless to say, more sophisticated models could also reproduce the signal, however, any model would have to exhibit the following 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 pointed out.