The ATLAS Z + MET Excess in the MSSM

Abstract

We demonstrate that the $3\sigma$ excess observed by ATLAS in the Z + MET channel can be explained within the context of the MSSM. Using the freedom inherent in the pMSSM, we perform a detailed analysis of the parameter space and find a scenario that describes the excess while simultaneously complying with all other search constraints from the Run I data at 7 and 8 TeV, including the Z + MET analysis by CMS. We generate a small sample of simplified models, using promising models from our existing pMSSM sample as seeds, and study their properties. The successful region is described by the production of 1st/2nd generation squark pairs, followed by their decay into a bino-like neutralino which in turn decays into a Higgsino-like LSP triplet by emitting a Z boson, i.e., $\tilde{q}\to \tilde{B}\to \tilde{h}$ with $\tilde{q}={\tilde{Q}}_L,{\tilde{u}}_R,$ or ${\tilde{d}}_R$. The sweet spot for the sparticle spectrum is found to have squark masses in the 500-750 GeV range, with bino masses near 350 GeV with a mass splitting of 150-200 GeV with the Higgsino LSP. If this excess holds, then this scenario predicts that a signal will be observed in the 0l + jets and/or 1l + jets searches in the early operations of Run II.

20 pages, 11 figures

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• ATLAS on-Z Excess Through Vector-Like Quarks
• Models of 750 GeV quarkonium and the LHC excesses
• Mixed Stops and the ATLAS on-Z Excess
• ATLAS on-Z Excess via gluino-Higgsino-singlino decay chains in the NMSSM
• Testing ATLAS Z+MET Excess with LHC Run 2
• Aspects of astrophysical particle production and beyond the Standard Model phenomenology
• pMSSM SUSY and the ATLAS Z+jets+MET Excess