Unraveling the CP phase of top-Higgs coupling in associated production at the LHC

Saurabh D Rindani,Ambresh Shivaji,Pankaj Sharma

doi:10.1016/j.physletb.2016.08.002

Abstract

We study the sensitivity of top polarization observables to the CP phase $\zeta_t$ in the top Yukawa coupling in the process $pp\to thj$ at the 14 TeV high-luminosity run of the Large Hadron Collider (HL-LHC). We calculate the top polarization in this process as well as an azimuthal asymmetry of the charged lepton arising from the decay of the top in the lab frame. We find that the dependence of this lab-frame azimuthal asymmetry on the phase $\zeta_t$ closely resembles the dependence of the top polarization on $\zeta_t$. As compared to the cross section, which is sensitive to $\zeta_t$ for larger values, the lepton azimuthal asymmetry can provide a sensitive measurement of $\zeta_t$ for smaller values.

Highlights

Particle physics has entered a new era with the discovery at the Large Hadron Collider (LHC) of a spin-0 particle of mass around 125 GeV in its first run [1, 2]
In the production plane of the top-quark, we deinfe an azimuthal asymmetry, which is the “left-right asymmetry” of the charged lepton at the LHC defined with respect to
The fact that a pseudoscalar does not couple to the EW gauge bosons at tree level spurs the idea of studying the CP properties of the Higgs in fermionic Yukawa couplings as they are more democratic to CP even and odd scalars

Summary

INTRODUCTION

Particle physics has entered a new era with the discovery at the Large Hadron Collider (LHC) of a spin-0 particle of mass around 125 GeV in its first run [1, 2]. We focus on thj production in the presence of the CP-violating phase ζt of the top Yukawa coupling at the 14 TeV LHC and examine the possibility of using top polarization and other angular observables constructed from top decay products in the top rest frame as well as the laboratory (lab) frame to measure this phase. Since earlier work has largely focused on measurement of cross sections and of top polarization through decay distributions in the top rest frame to enable the determination of the top Yukawa coupling and its phase ζt, our main emphasis will be to show how lab-frame observables can be used to probe ζt.

EFFECTIVE TOP-YUKAWA COUPLINGS

SIGNAL AND BACKGROUNDS

Γf dΓf d cos θf

ASYMMETRIES

Findings

CONCLUSIONS