Testing Leptoquark/EFT in $\bar B \to D^{(*)} l\bar\nu$ at the LHC

TL;DR

This paper compares leptoquark and EFT models in explaining B meson decays at the LHC, highlighting the limitations of EFT for low-mass leptoquarks and discussing future high-luminosity search prospects.

Contribution

It demonstrates the invalidity of EFT for leptoquark masses below 10 TeV at the LHC and clarifies the differences in bounds derived from LQ and EFT models.

Findings

EFT bounds overestimate for LQ masses below 10 TeV.

LHC constraints are comparable to flavor bounds in some NP scenarios.

Future high-luminosity LHC can improve sensitivity to NP signals.

Abstract

We investigate the current LHC bounds on New Physics (NP) that contributes to $\bar B \to D^{(*)} l\bar\nu$ for $l = (e,\mu,\tau)$ by considering both leptoquark (LQ) models and an effective-field-theory (EFT) Hamiltonian. Experimental analyses from $l+\text{missing}$ searches with high $p_T$ are applied to evaluate the NP constraints with respect to the Wilson coefficients. A novel point of this work is to show difference between LQs and EFT for the applicable LHC bound. In particular, we find that the EFT description is not valid to search for LQs with the mass less than $\lesssim 10\,\text{TeV}$ at the LHC and leads to overestimated bounds. We also discuss future prospects of high luminosity LHC searches including the charge asymmetry of background and signal events. Finally, a combined summary for the flavor and LHC bounds is given, and then we see that in several NP scenarios the LHC constraints are comparable with the flavor ones.