ATLAS Z-peaked excess in MSSM with a light sbottom or stop

TL;DR

This paper investigates whether a simplified MSSM scenario with light sbottom or stop can explain the ATLAS Z-peaked excess in dilepton events, considering constraints from LHC searches and decay chain dynamics.

Contribution

It introduces a specific decay chain in MSSM that could account for the ATLAS Z-excess and analyzes its viability under current experimental constraints.

Findings

The Z-excess can be marginally explained at 2σ level with light sbottom scenario.

The scenario with a light stop cannot explain the excess due to decay channel limitations.

Constraints from LHC searches restrict the parameter space for explaining the excess.

Abstract

We attempt to explain the recent ATLAS 3$\sigma$ excess of dilepton events with an invariant mass near $Z$ peak through the gluino-mediated sbottom production in a simplified scenario inspired by the Minimal Supersymmetric Standard Model (MSSM). The additional $Z$ bosons can be produced through the cascade decay chain $\tilde{g} \to b \tilde{b}^{\dagger}_{1} \to b \bar{b} \tilde{\chi}^{0}_{2,3} \to b \bar{b} \tilde{\chi}^{0}_1 Z$, in which $\tilde b_1$ is the right-handed sbottom, $\tilde\chi_1^0$ is the bino-like lightest supersymmetric particle (LSP) and $\tilde\chi_{2,3}^0$ are two nearly degenerate higgsino-like next-to LSPs (NLSPs). Taking into account the constraint from the LHC search for the gluino-mediated sbottom production in the final states with the missing transverse energy and at least three $b$-jets, we find that the ATLAS on-$Z$ excess can only be marginally explained at $2\sigma$ level. We also note that within the scenario where the gluino predominantly decays to the right-handed stop instead of the sbottom, the excess can hardly be explained, since the $Z$-boson is not produced in the stop dominant decay channel, $\tilde{t}_1 \to b \tilde{\chi}^+_1$.