On Drell-Yan production of scalar leptoquarks coupling to heavy-quark flavours

Abstract

Given the hints of lepton-flavour non-universality in semi-leptonic B decays, leptoquark (LQ) models with sizeable couplings to heavy-quark flavours are enjoying a renaissance. While such models are subject to stringent constraints from low-energy experiments also bounds from non-resonant dilepton searches at the Large Hadron Collider (LHC) turn out to be phenomenologically relevant. Based on the latest LHC dilepton analyses corresponding to an integrated luminosity of around 140 fb−1 of proton-proton collisions at $$ \sqrt{s} $$ s = 13 TeV, we present improved limits on the scalar LQ couplings that involve heavy-quark flavours and light or heavy dileptons. In particular, we show that effects beyond the leading order that are related to real QCD emissions are relevant in this context, since the inclusion of additional heavy-flavoured jets notably improves the exclusion limits that derive from the high-mass dilepton tails. The impact of electroweak corrections and interference effects between signal and background is also analysed. Within the POWHEG-BOX framework we provide a dedicated Monte Carlo code that allows for an on-the-fly signal event generation including all the LQ corrections considered in this article.

Drell-Yan production in third-generation gauge vector leptoquark models at NLO+PS in QCD

“…This allows for a realistic exclusive description of DY dilepton processes in singlet vector LQ models at the level of hadronic events. Similar calculations have been performed in the case of scalar LQs in [83,84] and the work presented in the following constitutes a non-trivial extension of our previous article [84]. The added complications that arise here are related to the fact that unambiguous NLO QCD calculations are only possible in the case of a massive vector LQ if the corresponding field is embedded into a consistent ultraviolet (UV) complete model.…”

“…The actual computation involves the evaluation of the real and virtual corrections to the t-channel Born-level contribution and the calculation of resonant single-LQ production followed by the decay of the LQ. One complication compared to the computation of O(α s ) corrections to DY dilepton production in scalar LQ models [83,84] arises from the fact that realistic vector LQ models such as the 4321 model (2.7) contain additional states that carry non-zero SU(3) C charges. In fact, in the case at hand both gluon and coloron exchange has to be considered in order to determine the full NLO QCD contributions to DY dilepton production.…”

“…Since these ditau signatures result from bottom-quark fusion, initial-state radiation will always lead to an enhanced b -jet activity in the events. Devising search strategies with different b -jet categories is therefore expected to help improve the LHC sensitivity [51,54,55,67,71,84,[89][90][91][92][93][94]. To illustrate this point, we have performed a recast of the search [54] that employs 138 fb −1 of pp data collected at √ s = 13 TeV.…”

“…In our phenomenological analysis we discuss the numerical impact of the NLO QCD corrections on the kinematic distributions that enter the existing ATLAS and CMS searches for non-resonant phenomena in τ + τ − final states. Since it is known that the requirement of additional final-state jets containing the decay of a B hadron (b -jets) helps to improve the LHC sensitivity of third-generation LQ searches [51,54,55,67,71,84,[89][90][91][92][93][94] we pay special attention to this feature in our study. Based on our DY ditau analyses we are able to derive improved limits on the parameter space of third-generation singlet vector LQ models using the results [54] that utilise the full LHC Run II integrated luminosity of 138 fb −1 obtained for proton-proton (pp) collisions at a centre-of-mass energy of √ s = 13 TeV.…”

Drell-Yan tails beyond the Standard Model

“…Our study leaves room for a few improvements needed to fully exploit the potential of LHC data to constrain flavor-physics scenarios. These include the incorporation of electroweak and QCD corrections to the LHC observables for the SMEFT [146,147] and leptoquark models [148], and the joint determination of quark PDFs and the BSM couplings [149], which would increase the accuracy of our constraints. The measurement of double differential-distributions is also a direction to be explored, as it could provide a useful handle to increase the sensitivity of Drell-Yan searches to New Physics effects [150].…”