LHC constraints and prospects for S 1 scalar leptoquark explaining the B ¯ → D ( * ) τ ν ¯ anomaly

Recently, deviations in flavor observables of $\overline{B}\ensuremath{\rightarrow}{D}^{(*)}\ensuremath{\tau}\overline{\ensuremath{\nu}}$ have been shown between the predictions in the Standard Model and the experimental results reported by BABAR, Belle, and LHCb collaborations. One of the solutions to this anomaly is obtained in a class of leptoquark model with a scalar leptoquark boson ${S}_{1}$, which is a $SU(3{)}_{c}$ triplet and $SU(2{)}_{L}$ singlet particle with $\ensuremath{-}1/3$ hypercharge interacting with a quark-lepton pair. With well-adjusted couplings, this model can explain the anomaly and be compatible with all flavor constraints. In such a case, the ${S}_{1}$ boson can be pair-produced at CERN's Large Hadron Collider (LHC) and subsequently decay as ${S}_{1}^{*}\ensuremath{\rightarrow}t\ensuremath{\tau}$, $b{\ensuremath{\nu}}_{\ensuremath{\tau}}$, and $c\ensuremath{\tau}$. This paper explores the current 8 and 13 TeV constraints, as well as the detailed prospects at 14 TeV, of this flavor-motivated ${S}_{1}$ model. From the current available 8 and 13 TeV LHC searches, we obtain constraints on the ${S}_{1}$ boson mass for ${M}_{{S}_{1}}l400\char21{}640\text{ }\text{ }\mathrm{GeV}$ depending on values of the leptoquark couplings to fermions. Then we study future prospects for this scenario at the 14 TeV LHC using detailed cut analyses and evaluate exclusion and discovery potentials for the flavor-motivated ${S}_{1}$ leptoquark model from searches for the $(b\ensuremath{\nu})(\overline{b}\overline{\ensuremath{\nu}})$ and $(c\ensuremath{\tau})(\overline{c}\overline{\ensuremath{\tau}})$ final states. In the latter case, we consider several scenarios for the identification of charm jets. As a result, we find that the ${S}_{1}$ leptoquark origin of the $\overline{B}\ensuremath{\rightarrow}{D}^{(*)}\ensuremath{\tau}\overline{\ensuremath{\nu}}$ anomaly can be probed with ${M}_{{S}_{1}}\ensuremath{\lesssim}600/800\text{ }\text{ }\mathrm{GeV}$ at the 14 TeV LHC with $\mathcal{L}=300/3000\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ of accumulated data. One can also see that the 14 TeV LHC run II with $\mathcal{L}=300\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ can exclude the ${S}_{1}$ leptoquark boson up to ${M}_{{S}_{1}}\ensuremath{\sim}0.8\text{ }\text{ }\mathrm{TeV}$ at 95% confidence level, whereas a future 14 TeV LHC with $\mathcal{L}=3000\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ data has a potential to discover the ${S}_{1}$ leptoquark boson with its mass up to ${M}_{{S}_{1}}\ensuremath{\sim}1.1\text{ }\text{ }\mathrm{TeV}$ with over $5\ensuremath{\sigma}$ significance, from the $(b\ensuremath{\nu})(\overline{b}\overline{\ensuremath{\nu}})$ and/or $(c\ensuremath{\tau})(\overline{c}\overline{\ensuremath{\tau}})$ searches.