Abstract
We revisit scalar leptoquark pair-production at hadron colliders and significantly improve the level of precision of the cross section calculations. Apart from QCD contributions, we include lepton t-channel exchange diagrams that turn out to be relevant in the light of the recent B-anomalies. We evaluate all contributions at next-to-leading-order accuracy in QCD and resum, in the threshold regime, soft-gluon radiation at next-to-next-to-leading logarithmic accuracy. Our predictions consist hence in the most precise leptoquark cross section calculations available to date, and are necessary for the best exploitation of leptoquark searches at the LHC.
Highlights
Many extensions of the Standard Model (SM) predict the existence of scalar leptoquarks [1,2,3,4,5,6,7,8], i.e., scalar bosons coupling to a quark and a lepton simultaneously
We evaluate all contributions at next-to-leading order in QCD and resum, in the threshold regime, soft-gluon radiation at next-to-next-to-leading-logarithmic accuracy
NNLL effects, which we estimate through the ratio of the NLO-QCD þ NNLL to the NLO-QCD cross sections both calculated with the same NLO parton distribution functions (PDFs) set, are independent of the process and PDF choice
Summary
Many extensions of the Standard Model (SM) predict the existence of scalar leptoquarks [1,2,3,4,5,6,7,8], i.e., scalar bosons coupling to a quark and a lepton simultaneously. Scalar leptoquarks have gained significant interest as they may provide an explanation [16,17,18,19,20,21,22] for the B-meson anomalies [23,24,25,26,27,28,29,30] and address [31] the discrepancy between theoretical predictions [32] and experimental measurements [33] of the anomalous magnetic moment of the muon ðg − 2Þμ In this context, favored scenarios generally feature large lepton-quark-leptoquark Yukawa couplings y. Hadronic production of heavy systems, which is the case considered here, inevitably probes partonic center-of-mass energies close to the production threshold given by twice the leptoquark mass mLQ In this limit, radiative corrections are dominated by soft-gluon emissions, manifesting themselves as large logarithmic terms that must be consistently resummed to all orders [36,37,38,39]. Our predictions, which are the most precise to date, are required to derive limits consistently, in particular when assessing the influence of the leptoquark Yukawa couplings
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