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

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, $\tilde{t}_1 \to b \tilde{\chi}^+_1$.