Hunting for scalar leptoquarks with boosted tops and light leptons

Abstract

The LHC search strategies for leptoquarks that couple dominantly to a top quark are different than for the ones that couple mostly to the light quarks. We consider charge 1/3 (φ1) and 5/3 (φ5) scalar leptoquarks that can decay to a top quark and a charged lepton (tℓ) giving rise to a resonance system of a boosted top and a high-pT lepton. We introduce simple phenomenological models suitable for bottom-up studies and explicitly map them to all possible scalar leptoquark models within the Buchmüller-Rückl-Wyler classifications that can have the desired decays. We study pair and single productions of these leptoquarks. Contrary to the common perception, we find that the single production of top-philic leptoquarks φ={φ1,φ5} in association with a lepton and jets could be significant for order one φtℓ coupling in certain scenarios. We propose a strategy of selecting events with at least one hadronic-top and two high-pT same flavor opposite sign leptons. This captures events from both pair and single productions. Our strategy can significantly enhance the LHC discovery potential especially in the high-mass region where single productions become more prominent. Our estimation shows that a scalar leptoquark as heavy as ∼1.7 TeV can be discovered at the 14 TeV LHC with 3 ab-1 of integrated luminosity in the tℓℓ+X channel for 100% branching ratio in the φ→tℓ decay mode. However, in some scenarios, the discovery reach can increase beyond 2 TeV even though the branching ratio comes down to about 50%.