Azimuthal correlation among jets produced in association with a bottom or top quark pair at the LHC

TL;DR

This paper analyzes jet angular correlations in events with top or bottom quark pairs plus two jets at the LHC to help determine the spin and CP properties of new particles produced via gluon fusion.

Contribution

It provides analytic expressions for azimuthal angle correlations in heavy quark pair plus jets events, aiding in spin and CP property measurements of new particles at the LHC.

Findings

Strong azimuthal correlations for b b-bar + 2 jets distinguish CP-even/odd scalars.

Similar angular patterns for t t-bar + 2 jets near threshold and relativistic limits.

Method helps in experimental determination of particle spin and CP properties.

Abstract

Angular correlation of jets produced in association with a massive scalar, vector or tensor boson is crucial in the determination of their spin and CP properties. We study jet angular correlations in events with a high mass bottom quark pair or a top quark pair and two jets at the LHC, whose cross-section is dominated by the virtual gluon fusion sub-processes when appropriate kinematic selection cuts (vector-boson fusion cuts) are applied. We evaluate helicity amplitudes for sub-processes initiated by qq, qg and gg collisions in the limit where the intermediate gluons are collinear to the initial partons. We first obtain a general expression for the azimuthal angle correlations among the dijets and t t-bar or b b-bar, in terms of the gg to t t-bar or b b-bar helicity amplitudes in the real gluon approximation of the full matrix elements, and find simple analytic expressions in the two kinematic limits, the production of a heavy quark pair near the threshold, and in the relativistic limit where the invariant mass of the heavy quark pair is much larger than the quark mass. For b b-bar + 2 jets we find strong azimuthal angle correlations which are distinct from those expected for events with a CP-even or odd scalar boson which may decay into a b b-bar pair. For t t-bar + 2 jets we find that the angular correlations are similar to that of a CP-odd scalar+2 jets near the threshold M_(t t-bar) ~ 2 m_t, while in the relativistic limit they resemble the distribution for b b-bar + 2 jets. These correlations in the standard QCD processes will help establish the experimental technique to measure the spin and CP properties of new particles produced via gluon fusion at the LHC.