The role of the S3 GUT leptoquark in flavor universality and collider searches

Abstract

We investigate the ability of the S3 scalar leptoquark to address the recent hints of lepton universality violation in B meson decays. The S3 leptoquark with quantum numbers left(overline{mathbf{3}},mathbf{3},1/3right) naturally emerges in the context of an SU(5) GUT model without any conflict with the stringent limits from observed nucleon stability. Scalar leptoquark S3 with left-handed couplings to 2nd and 3rd generations of charged leptons and down-type quarks seems well-suited to address both RK(∗) and RD(∗) . We quantify this suitability with numerical fits to a plethora of relevant flavor observables. The proposed SU(5) model calls for a second leptoquark state, i.e., {tilde{R}}_2 with quantum numbers (3,2, 1/6), if one is to generate gauge coupling unification and neutrino mass. We accordingly include it in our study to investigate {tilde{R}}_2 ’s ability to offset adverse effects of S3 and thus improve a quality of numerical fits. A global fit of the leptoquark Yukawa couplings shows that large couplings of light S3 to τ leptons are preferred. We furthermore identify Bto {K}^{left(ast right)}overline{nu}nu as the most sensitive channel to probe the preferred region of parameter space. Large couplings of S3 to τ leptons are finally confronted with the experimental searches for τ final states at the Large Hadron Collider. These searches comprise a study of decay products of the leptoquark pair production, as well as, and more importantly, an analysis of the high-mass ττ finalstates.