LHC Bounds on $R_{D^{(*)}}$ motivated Leptoquark Models

TL;DR

This paper uses current LHC data, especially ATLAS $ au au$ resonance searches, to set new constraints on specific leptoquark models that could explain anomalies in B-meson decays, focusing on their impact on $R_{D^{(*)}}$.

Contribution

It provides the first recasting of ATLAS $ au au$ resonance data to constrain $S_1$ and $U_1$ leptoquark models relevant for $R_{D^{(*)}}$ anomalies.

Findings

Established new exclusion limits on $S_1$ and $U_1$ leptoquark couplings.

Demonstrated the importance of non-resonant $t$-channel contributions.

Showed limits are competitive with existing bounds.

Abstract

Most of the popular explanations of the observed anomalies in the semileptonic $B$-meson decays involve TeV scale Leptoquarks (LQs). Among the various possible LQ models, two particular LQs -- $S_{1}(3, 1, 1/3)$ and $U_{1}(3, 1, 2/3)$ seem to be most promising. Here, we use current LHC data to constrain the $S_{1}(3, 1, 1/3)$ and $U_{1}(3, 1, 2/3)$ parameter spaces relevant for the $R_{D^{(*)}}$ observables. We recast the latest ATLAS $\tau\tau$ resonance search data to obtain new exclusion limits. For this purpose, we consider both resonant (pair and single productions) and non-resonant ($t$-channel LQ exchange) productions of these LQs at the LHC. For the limits, the most dominant contribution comes from the (destructive) interference of the non-resonant production with Standard Model backgrounds. The combined contribution from the pair and inclusive single production processes is less prominent but non-negligible. The limits we get are independent and competitive to other known bounds. For both the models, we set limits on $R_{D^{(*)}}$ motivated couplings.