LHC Bounds on R$_{D^{(*)}}$ Motivated Leptoquark Models

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 Mandal et al (JHEP, 07:028, 2015, [1]) 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 Mandal et al (Phys Rev D 99(5):055028, 2019, [2]), Bhaskar et al (Phys Rev D 104(3):035016, 2021, [3]).