Speaker
Description
In this paper we examine the constraints dedicated LHC multi lepton searches can place on $Z'$ bosons coming from gauged muon number minus tau number, $L_{\mu}-L_{\tau}$. As the $L_{\mu}-L_{\tau}$ gauge boson does not couple to proton constituents or electrons at tree level, the current bounds are fairly loose, especially for $M_{Z'} < 1~ \rm GeV$. For $2m_{\mu} < M_{Z'} < M_Z/2$ we develop search strategies using the $pp \to Z \to 4\, \mu$ channel. The cleanliness of the final state, combined with the fact that $pp \to Z \to 4 e$, $Z \to 2e\,2\mu$ can be used as background control samples, allow us to spot $L_{\mu}-L_{\tau}$ $Z'$ with couplings $\mathcal O(10^{-4})$ times the Standard Model couplings with Matrix Element method. For lighter $Z'$, we propose the mode $pp \to 2\mu + \displaystyle{\not} E_T$. The presence of missing energy means there is a wider set of backgrounds to consider in this final state, such as Drell-Yan production of leptonically decaying $\tau$ pairs, however we find these can be controlled with careful cuts.
Summary
we examine the constraints dedicated LHC multi lepton searches can place on $Z'$ bosons coming from gauged muon number minus tau number, $L_{\mu}-L_{\tau}$, where $M_{Z'}< M_{Z}/2$.
