Cornering scalar leptoquarks at LHC

Abstract

We study implications of large lepton-quark-leptoquark couplings for direct leptoquark searches at Large Hadron Collider. We present all existing flavor constraints on the strength of these couplings assuming that leptoquarks under consideration interact exclusively with charged leptons and quarks of the same generation. We find that these leptoquarks can have sizeable couplings to the Standard Model fermions. This insures a self consistency of our study. We discuss the leptoquark production mechanisms at LHC and demonstrate the importance of inclusion of a t-channel pair production and, in particular, a single leptoquark production through a recast of an existing CMS search at LHC for the second generation leptoquark. Our recast yields the best direct limit on Yukawa coupling of the second generation leptoquark that couples to a muon and a strange quark to date.

Observable effects of general new scalar particles

“…In all cases the limits apply to ratios of couplings and masses, which are the quantities that appear in the coefficients of the effective operators. (In some cases tailored searches can give better bounds when the new scalars can be directly produced [46].) Let us comment on the few absences in those tables.…”

Lepton flavor nonuniversality inb→sℓ+ℓ−processes

“…It indeed verifies the relation, C 9 = −C 10 [9], and leads to a consistency with the measured value of R K . The features of this leptoquark state have been already described in the literature [26]. While there is no theoretical motivation to forbid leptoquark contributing to b → see decays, simultaneous presence of both muonic and electronic couplings could be problematic because they would, together, induce lepton flavor violation in B s → eµ and µ → eγ decays.…”

“…It is interesting that the flavor physics constraints at low energies agree and are complementary with the constraints obtained from the direct experimental searches at LHC [27,28]. Furthermore, the atomic parity violation experiments provided a strong constraint on the interaction of the down-quark-electron interaction with the leptoquark state [26,29], while the couplings to muons appear to be less constrained via B(K L → µ ± e ∓ ) < 4.7 × 10 −12 [26,30]. We therefore assume in our analysis that in the b → s + − processes only the muons can interact with the leptoquark state.…”

Constraints on leptoquark models from IceCube data

“…Leptoquark can be produced, singly or doubly, at colliders (hadron, e + e − or e ± p) and signals (like the jj from the decay of a leptoquark pair) and other important properties and constraints can be studied [8][9][10][11][12][13][14][15][16][17][18][19]. A search for pair-production of first and second generation scalar LQs has been performed with 19.6 fb −1 of data by CMS [20,21].…”