Disentangling Higgs-top couplings in associated production

Abstract

In the presence of CP violation, the Higgs-top coupling may have both scalar and pseudoscalar components, κ t andκ t , which are bounded indirectly but only weakly by the present experimental constraints on the Higgs-gluon-gluon and Higgs-γ-γ couplings, whereas upper limits on electric dipole moments provide strong additional indirect constraints onκ t , if the Higgs-electron coupling is similar to that in the Standard Model and there are no cancellations with other contributions. We discuss methods to measure directly the scalar and pseudoscalar Higgs-top couplings by measurements of Higgs production in association with tt, single t and singlet at the LHC. Measurements of the total cross sections are very sensitive to variations in the Higgs-top couplings that are consistent with the present indirect constraints, as are invariant mass distributions inttH, tH andtH final states. We also investigate the additional information on κ t andκ t that could be obtained from measurements of the longitudinal and transverse t polarization in the different associated production channels, and thett spin correlation inttH events. It is important to characterize the new boson H discovered by the ATLAS [1] and CMS [2]Collaborations. In this paper we refer to this particle as a Higgs boson, since it has some of the expected properties, though others remain to be verified. Tests via H decays into γγ [3], W W * [4] and ZZ * [5,6] are consistent with it having spin zero [7][8][9][10][11], as are measurements of H production in association with W and Z [12]. In particular, these tests exclude gravitonlike spin-two couplings with a high degree of confidence. Assuming that the H spin is indeed zero, the next question is whether it has scalar and/or pseudoscalar couplings.Tests in W W * and ZZ * final states [5][6][7][8][13][14][15][16][17] and production in association with W and Z [12] also disfavour strongly pure pseudoscalar couplings, but do not yet exclude a substantial pseudoscalar admixture. In the presence of CP violation, the ratios of scalar and pseudoscalar couplings may differ from channel to channel, and it is important to measure them in as many different channels as possible. Strategies to measure a CP-violating admixture in H → τ + τ − decays have been proposed [18-20], and other tests are possible in H production in vector-boson fusion [21-25], double-diffractive [26, 27] and γγ collisions [28]. There are already indirect constraints on the scalar and pseudoscalar H-top couplings κ t andκ t from experimental information on the H-gluon-gluon and H-γ-γ couplings [29], but these constraints are relatively weak [40], as we discuss later. Upper limits on electric dipole moments also impose important indirect constraints on a possible pseudoscalar H-top couplingκ t [29], if one assumes that if the Higgs-electron coupling is similar to that in the Standard Model and there are no cancellations with other contributing mechanisms.In this paper we investigate the potential for disentangling scalar and pseudoscalar Htop couplings ...

Large pseudoscalar Yukawa couplings in the complex 2HDM

“…There are several proposals for a direct measurement of this ratio, which focus mainly on the tth and on the τ + τ − h couplings. Measurement of b U /a U were first proposed for pp → tth in [62] and more recently reviewed in [63][64][65]. A proposal to probe the same vertex through the process pp → hjj [66] was put forward in [67] and again more recently in [68].…”

Enhancing thj production from top-Higgs FCNC couplings

“…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.…”

ProbingCP-violatinght¯tcoupling ine+e<

“…The signal strengths measured in gg → h and h → γγ have constrained the CP phase |ξ| ≤ 3π/5 at 95% C.L. [23,27] 1 . On the other hand, the electric dipole moment (EDM) of the electron d e constrains the upper limit on the CP-odd coupling |κ t sin ξ| < 0.01 with the assumption of SM-like hēe coupling [36].…”

“…10 shows the signal and bkg distributions of the invariant mass of bb and the photon's recoil energy following the basic selection cuts (a) in Eq. (23). So the mass window cut ∼ 15 GeV and the requirement of the photon energy resolution are efficient to improve the signal significance.…”