Role of the t t ¯ h rest frame in direct top-quark Yukawa coupling measurements
Abstract
This paper studies new possibilities to directly measure a hypothetical C P -odd (pseudoscalar) component in the top-quark Yukawa coupling. In particular, the role of the t t ¯h center-of-mass rest frame in the associated production of a top pair and a h boson at the LHC is explored. The h boson is assumed to have both a C P -even (scalar) and a C P -odd coupling to the top quark. The relative strength of the scalar and pseudoscalar components is regulated by an angle α . Observables sensitive to the nature of the top-quark Yukawa coupling are proposed. These observables are defined in terms of the transverse and longitudinal projections of t , t ¯ and h momenta with respect to the beam axis in the t t ¯h rest frame. Distributions differential with respect to those observables are evaluated up to next-to-leading order in QCD. These distributions are found to be sensitive to the C P nature of the coupling. Dileptonic final states of the t t ¯h system (with h →b b ¯) are used, after fast uc(d)ELPHES detector simulation and full event reconstruction through a kinematic fit, as a case study to test the observables' sensitivity to the C P nature of the coupling. Confidence levels are presented as a function of the total integrated LHC luminosity for the case of exclusion of a pure C P -odd coupling against the Standard Model C P -even hypothesis. By using observables evaluated in the t t ¯h system, the luminosity needed to directly probe the C P properties of the top-quark Yukawa coupling at the High-Luminosity run of the LHC can be decreased by a few hundred inverse femtobarns, when compared to analyses that use observables in the laboratory rest frame. In addition, transverse momentum distributions of the h boson and top quarks are found to provide no more discriminant power than a counting experiment.
- Publication:
-
Physical Review D
- Pub Date:
- October 2019
- DOI:
- 10.1103/PhysRevD.100.075034
- arXiv:
- arXiv:1909.00490
- Bibcode:
- 2019PhRvD.100g5034F
- Keywords:
-
- High Energy Physics - Phenomenology
- E-Print:
- 15 pages, 14 figures