Explanation of the ATLAS Z-peaked excess in the NMSSM

Abstract

Recently the ATLAS collaboration reported a $3\sigma$ excess in the leptonic-$Z+jets+E_T^{miss}$ channel. This may be interpreted in the Next-to-Minimal Supersymmetric Standard Model (NMSSM) by gluino pair production with the decay chain $\tilde{g}\to q\bar{q}{\tilde{\chi }}_2^0\to q\bar{q}Z{\tilde{\chi }}_1^0$, where ${\tilde{\chi }}_1^0$ and ${\tilde{\chi }}_2^0$ denote the lightest and the next-to-lightest neutralinos with singlino and bino as their dominant components respectively. After exploring the relevant parameter space of the NMSSM by considering the constraints from the ATLAS searches for $jets+E_T^{miss}$ signals, we conclude that the NMSSM is able to explain the excess at $1\sigma$ level with the number of the signal events reaching its measured central value in optimal cases, and the best explanation comes from a compressed spectrum such as $m_{\tilde{g}}\simeq 650\mathrm{GeV}$, $m_{{\tilde{\chi }}_2^0}\simeq 565\mathrm{GeV}$ and $m_{{\tilde{\chi }}_1^0}\simeq 465\mathrm{GeV}$. We also check the consistency of the ATLAS results with the null result of the CMS on-$Z$ search. We find that under the CMS limits at $95\%$ C.L., the event number of the ATLAS on-$Z$ signal can still reach 11 in our scenario, which is about $1.2\sigma$ away from the measured central value.

Comments: 18 pages, 2 figures