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 $\tilde{g}\to b{\tilde{b}}_1^{†}\to b\bar{b}{\tilde{\chi }}_{2,3}^0\to b\bar{b}{\tilde{\chi }}_1^{0}Z$, 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, ${\tilde{t}}_1\to b{\tilde{\chi }}_1^{+}$.

Comments: 4 pages, 3 figures, discussions added, tables and figures updated, version accepted by Phys. Rev. D