Probing the CP nature of the Higgs coupling in tt¯h events at the LHC

Abstract

The determination of the CP nature of the Higgs coupling to top quarks is addressed in this paper, using tth events produced in √ s = 13 TeV proton-proton collisions at the LHC. Dileptonic final states are employed, with two oppositely charged leptons and four jets, corresponding to the decays t → bW + → b + ν ,t →bW − →b −ν and h → bb. Pure scalar (h = H), pure pseudo-scalar (h = A) and CP-violating Higgs boson signal events, generated with MadGraph5_aMC@NLO, are fully reconstructed through a kinematic fit. We furthermore generate samples that have both a CP-even and a CP-odd component in the tth coupling in order to probe the ratio of the two components. New angular distributions of the decay products, as well as CP angular asymmetries, are explored in order to separate the scalar from the pseudo-scalar components of the Higgs boson and reduce the contribution from the dominant irreducible background, ttbb. Significant differences between the angular distributions and asymmetries are observed, even after the full kinematic fit reconstruction of the events, allowing to define the best observables for a global fit of the Higgs couplings parameters.

CP tests of Higgs couplings in tt¯h semileptonic events at the LHC

“…Moreover, background discrimination in this channel can be enhanced using these angular variables. Although results are consistent with what was observed in an analysis of the dileptonic tth channel [17,18], the signal sensitivity of the semileptonic analysis reported here is larger than the dileptonic one. As in the dileptonic analysis [18], all the mixed states of CP-even and CP-odd couplings gave results between the ones obtained with cos α ¼ 0 and cos α ¼ 1; only these two extreme cases are considered in the present analysis.…”

“…Equivalent results for the tth dileptonic final state, published in Ref. [18], are presented on the right-hand side for comparison. The reconstruction using KLFITTER performs better than the one used in the dileptonic channel, avoiding, for instance, the asymmetries seen in the transverse momentum of the Higgs boson (top left).…”

“…We would like to thank S. Amor Dos Santos et al for providing the angular distributions from their analysis in the dileptonic channel [17,18] …”

CP Properties of Higgs Boson Interactions with Top Quarks in the tt¯H and tHAad1, Abbott2, Abbott3 et al. 2020Phys. Rev. Lett.Self Cite673530View full textAdd to dashboardCite

“…The CP properties of the top Yukawa coupling can be probed directly using Higgs boson production in association with top quarks: ttH and tH processes. The couplings impact the production rates [11][12][13][14] and some kinematic distributions. The tH rate is particularly sensitive to deviations from SM couplings due to destructive interference in the SM between diagrams where the Higgs boson radiates from a top quark and from a W boson.…”

Probing the top-Higgs Yukawa CP structure in dileptonic $$ t\overline{t}h $$ with M2-assisted reconstruction

“…For example, ref. [84] performs a conventional kinematic mass reconstruction with the missing transverse momentum and attempts resolving the two-fold sign ambiguity using a likelihood based on transverse momenta of the involved particles. This method leads to 62% efficiency with 50% purity for signal, and 51% efficiency for backgrounds.…”