Search for $t{Z}^{\prime }$ associated production induced by $tc{Z}^{\prime }$ couplings at the LHC

Abstract

The $P_5^{\prime }$ and $R_K$ anomalies, recently observed by the LHCb collaboration in $B\to K^{(\ast )}$ transitions, may indicate the existence of a new $Z^{\prime }$ boson, which may arise from gauged $L_{\mu }-L_{\tau }$ symmetry. Flavor-changing neutral current $Z^{\prime }$ couplings, such as $tc{Z}^{\prime }$, can be induced by the presence of extra vector-like quarks. In this paper we study the LHC signatures of the induced right-handed $tc{Z}^{\prime }$ coupling that is inspired by, but not directly linked to, the $B\to K^{(\ast )}$ anomalies. The specific processes studied are $cg\to t{Z}^{\prime }$ and its conjugate process each followed by $Z^{\prime }\to {\mu }^{+}{\mu }^{-}$. By constructing an effective theory for the $tc{Z}^{\prime }$ coupling, we first explore model-independently the discovery potential of such a $Z^{\prime }$ at the 14 TeV LHC with 300 and 3000 fb${}^{-1}$ integrated luminosities. We then reinterpret the model-independent results within the gauged $L_{\mu }-L_{\tau }$ model. In connection with $tc{Z}^{\prime }$, the model also implies the existence of a flavor-conserving $cc{Z}^{\prime }$ coupling, which can drive the $c\bar{c}\to Z^{\prime }\to {\mu }^{+}{\mu }^{-}$ process. Our study shows that existing LHC results for dimuon resonance searches already constrain the $cc{Z}^{\prime }$ coupling, and that the $Z^{\prime }$ can be discovered in either or both of the $cg\to t{Z}^{\prime }$ and $c\bar{c}\to Z^{\prime }$ processes. We further discuss the sensitivity to the left-handed $tc{Z}^{\prime }$ coupling and find that the coupling values favored by the $B\to K^{(\ast )}$ anomalies lie slightly below the LHC discovery reach even with 3000 fb${}^{-1}$.

Comments: 14 pages, 18 figures, explanations added, matched with the published version