Lifting degeneracies in Higgs couplings using single top production in association with a Higgs boson

Abstract

Current Higgs data show an ambiguity in the value of the Yukawa couplings to quarks and leptons. Not so much because of still large uncertainties in the measurements but as the result of several almost degenerate minima in the coupling profile likelihood function. To break these degeneracies, it is important to identify and measure processes where the Higgs coupling to fermions interferes with other coupling(s). The most prominent example, the decay of h → γγ, is not sufficient to give a definitive answer. In this paper, we argue that t-channel single top production in association with a Higgs boson, with h → bb, can provide the necessary information to lift the remaining degeneracy in the top Yukawa. Within the Standard Model, the total rate is highly reduced due to an almost perfect destructive interference in the hard process, W b → th. We first show that for non-standard couplings the cross section can be reliably computed without worrying about corrections from physics beyond the cutoff scale Λ 10 TeV, and that it can be enhanced by more than one order of magnitude compared to the SM. We then study the signal pp → thj(b) with 3 and 4 b's in the final state, and its main backgrounds at the LHC. We find the 8 TeV run dataset to be sensitive to the sign of the anomalous top Yukawa coupling, while already a moderate integrated luminosity at 14 TeV should lift the degeneracy completely.

Enhancing thj production from top-Higgs FCNC couplings

“…• Case-(I ): when κ tqh = 0.1, the total cross section of pp → thj at 8 and 14 TeV LHC can be respectively enhanced up to nearly 176 and 145 times the SM predictions [76].…”

“…In the SM, the process pp → thj can only be induced by the weak charged current interaction and has a relative small cross section, which is about 18 (88) fb at 8 (14) TeV LHC. However, such a process is found to be very sensitive to modifications of the Higgs couplings [74][75][76][77][78][79][80][81]. In particular, the top-Higgs FCNC couplings tqh(q = u, c) can sizably enhance thj cross section due to the contributions from the strong interaction processes.…”

Effect of anomalous couplings on the associated production of a single top quark and a Higgs boson at the LHC

“…This change of sign leads to a constructive interference among the diagrams and thus a significant increase in the thj and thbj cross sections. It is argued that this enhancement can be detected at the LHC using various decay modes of the Higgs boson [5][6][7]. In this paper, we are not only considering this situation, but general anomalous tth coupling.…”

“…However, in this paper we shall not pursue the details of the possible new physics models, rather restrict ourselves to the study of the effect of the anomalous couplings that can appear in the W tb, tth and W W h vertices on the pp → thX process in the effective theory framework. Recently, there have also been a few studies that consider the change in the sign of the tth Yukawa coupling on the associated production of a single top quark and a Higgs boson [5][6][7]. This change of sign leads to a constructive interference among the diagrams and thus a significant increase in the thj and thbj cross sections.…”

“…However, since most of the jets in the signal processes are b-jets, we can use the tagging of the b-jets to reduce JHEP12(2013)077 the backgrounds. In particular, for the signature -"an isolated e/µ + 3 b-jets + light jets" [6], all of the processes under consideration can contribute. To isolate different signal processes, one has to look for other signatures.…”