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

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 $t\overline{t}$ or $b\overline{b}$, in terms of the gg → $t\overline{t}$ or $b\overline{b}$ 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 $b\overline{b}$ + 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 $b\overline{b}$ pair. For $t\overline{t}$ + 2 jets we find that the angular correlations are similar to that of a CP-odd scalar+2 jets near the threshold ${M_{{t\overline{t}}}}\sim 2{m_t}$, while in the relativistic limit they resemble the distribution for $b\overline{b}$ + 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.