Abstract
Evidence for electron-muon universality violation that has been revealed in b → sℓℓ transitions in the observables {R}_{KK^{ast }} by the LHCb Collaboration can be explained with spin-1 leptoquarks in SU(2)L singlet V1 or triplet V3 representations in the mathcal{O} (1 − 10) TeV range. We explore the sensitivity of the high luminosity LHC (HL-LHC) and future proton-proton colliders to V1 and V3 in the parameter space connected to {R}_{KK^{ast }} -data. We consider pair production and single production in association with muons in different flavor benchmarks. Reinterpreting a recent ATLAS search for scalar leptoquarks decaying to bμ and jμ, we extract improved limits for the leptoquark masses: for gauge boson-type leptoquarks (κ = 1) we obtain {M}_{V_1} > 1.9 TeV, {M}_{V_1} > 1.9 TeV, and {M}_{V_1} > 1.7 TeV for leptoquarks decaying predominantly according to hierarchical, flipped and democratic quark flavor structure, respectively. Future sensitivity projections based on extrapolations of existing ATLAS and CMS searches are worked out. We find that for κ = 1 the mass reach for pair (single) production of V1 can be up to 3 TeV (2.1 TeV) at the HL-LHC and up to 15 TeV (19.9 TeV) at the FCC-hh with sqrt{s} = 100 TeV and 20 ab−1. The mass limits and reach for the triplet V3 are similar or higher, depending on flavor. While there is the exciting possibility that leptoquarks addressing the {R}_{KK^{ast }} -anomalies are observed at the LHC, to fully cover the parameter space pp-collisions beyond the LHC-energies are needed.
Highlights
We consider pair production and single production in association with muons in different flavor benchmarks
We explore the sensitivity of the high luminosity LHC (HL-LHC) and future proton-proton colliders to V1 and V3 in the parameter space connected to RK,K∗-data
To quantitatively study the sensitivity to leptoquarks at the LHC and beyond, the leptoquark couplings to bottom- and to strange quarks have to be given individually, their product as in (1.1). This is obvious for single production, which feeds on the corresponding parton distribution functions in the proton, see figure 1, but matters for pair production [19], since the flavor patterns dictate the signature from leptoquark decay
Summary
We assume that one of the leptoquark representations, either V1(3, 1, 2/3) or V3(3, 3, 2/3), provides the resolution of the RK(∗) anomalies. The interactions of V1 and V3 with the standard model gauge bosons follow from the kinetic terms. Other renormalizable couplings of the leptoquark bilinear to weak boson field strengths Wμν and Bμν are irrelevant for the present study. We assume that only couplings to quark and lepton doublets are present and neglect couplings to singlet fermions in eq (2.1). This feature is not generic across possible UV completions and requires some model building, e.g. it does not hold in the minimal Pati-Salam model. Some of the proposed models in which V1 is a gauge boson include new vector-like fermions which render the coupling matrix λQL non-unitary. For a selection of references studying the V1 leptoquark in the context of the b → s transitions we refer the reader to refs. [13, 31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53]
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