Status of leptoquark models after LHC Run-2 and discovery prospects at future colliders

TL;DR

This paper evaluates the current constraints on leptoquark models from LHC Run-2 data and explores future collider prospects, focusing on their potential to explain anomalies in B-meson decays and their detectability at upcoming experiments.

Contribution

It provides the first comprehensive analysis of leptoquark model constraints using non-resonant dilepton searches and assesses future collider sensitivities for these models.

Findings

LHC Run-2 data already constrains some leptoquark parameter space.

Future muon colliders can probe all relevant vector leptoquark models with minimal data.

Exclusion limits vary depending on whether leptoquark couplings are universal or non-universal.

Abstract

We study limits from dilepton searches on leptoquark completions to the Standard Model in the parameter space motivated by anomalies in the $b \rightarrow s$ sector. After a full Run-2 analysis by LHCb, the disparity in lepton flavour violation has disappeared. However, the mismatch in angular distributions as well as in $B_s \rightarrow \mu^+ \mu^-$ partial width is still unresolved and still implies a possible new physics contribution. We probe three models of leptoquarks -- scalar models $S_3$ and $R_2$ as well as vector leptoquark model $U_1$ using non-resonant dilepton searches to place limit on both the mass and couplings to SM fermions. The exclusions of leptoquarks coupling either non-uniformly to different lepton flavours or uniformly is examined. Interestingly, if leptoquark couplings to electrons and muons are indeed universal, then the $U_1$ model parameter space that corresponds to the anomalous contribution should already accessible with Run-2 data in the non-resonant $e\mu$ channel. In the non-universal case, there is a significant exclusion in couplings, but not enough to reach regions that explain observed anomalies. We, therefore, examine the prospective sensitivity at the HL-LHC as well as of a 3 TeV future muon collider. For the vector leptoquark model, we find that a muon collider can probe all of the relevant parameter space at 95% confidence with just 1 fb$^{-1}$ data whereas $R_2$ and $S_3$ models can be excluded at 95% with 5 fb$^{-1}$ and 6.5 fb$^{-1}$ luminosity respectively.