Azimuthal Angle Correlations for Higgs Boson plus Multi-Jet Events

TL;DR

The paper develops a CP-sensitive observable for Higgs boson production in association with multiple jets by exploiting insights from the Multi-Regge Kinematics limit. It redefines the azimuthal angle as the angle between summed jet momenta on opposite sides of the Higgs (q_a and q_b) and optimizes cuts (notably y_sep) to enhance the correlation while preserving cross sections. Through fixed-order (hjj, hjjj), parton-shower, and all-order MRK-based analyses, it demonstrates that the observable remains remarkably stable against higher-order corrections and that all-order resummation reproduces the CP signal where parton showers can fail. These results support robust CP-structure extraction in Higgs+multi-jet events at the LHC, informing both analysis strategies and theoretical modeling.

Abstract

At lowest order in perturbation theory, the scattering matrix element for Higgs boson production in association with dijets displays a strong correlation in the azimuthal angle between the dijets, induced by the CP-properties of the Higgs Boson coupling. However, the phase space cuts necessary for a clean extraction of the CP-properties simultaneously induce large corrections from emissions of hard radiation and thus formation of extra jets. The current study concerns the generalization of CP-studies using the azimuthal angle between dijets beyond tree-level and to events with more than just two jets. By analyzing the High Energy Limit of hard scattering matrix elements we arrive at a set of cuts optimized to enhance the correlation, while maintaining a large cross section, and an observable, which is very stable against higher order corrections. We contrast the description of Higgs boson production in association with jets at different levels: for tree-level hjj and hjjj matrix elements, for hjj matrix elements plus parton shower, and in a recent all-order framework, which converges to the full, all-order perturbative result in the limit of large invariant mass between all produced particles.

Figures (12)

• Figure 1: $A_\phi$ vs. $\Delta y$ and $y^*$ with a bin size of $.25\times .25$ units of rapidity, for a SM Higgs boson of mass $m_h=120$ GeV. Insert: $d\sigma/(dy^*d\Delta y)$ in fb/bin.
• Figure 2: $(1/\sigma\ d\sigma/d\phi_{jj})$ for $hjj$-production at tree-level with the cuts of Eq. \ref{['eq:multijetcuts']} and $y_\mathrm{sep}=0.5,0.75,1.0$.
• Figure 3: $(1/\sigma\ d\sigma/d\phi_{jj})$ for production of the $CP$-odd higgs boson $A$ plus two jets at tree-level with the cuts of Eq. \ref{['eq:multijetcuts']} and $y_\mathrm{sep}=0.5,0.75,1.0$. The scales were chosen as described in Section \ref{['sec:parton-shower']}.
• Figure 4: The angular distribution (according to Eq. \ref{['eq:qaqb']}) for $y_\mathrm{sep}=0.75$ for both the two-jet sample and three different sub-samples of the three-jet sample (all jets above 40 GeV in transverse momentum --- see text for further details). The cuts and the definition of azimuthal angle in samples of more than two jets ensure that the distribution is very stable against perturbative corrections. The lines are fits on the form of Eq. \ref{['eq:fitform']} to the histograms.
• Figure 5: The angular distribution (according to Eq. \ref{['eq:qaqb']}) for $y_\mathrm{sep}=0.75$ for both the two-jet sample and a three-jet (all above 40 GeV in transverse momentum) sample of the two hardest jets on one side of the Higgs and a softer on the other (see text for further details). The characteristic azimuthal dependence is not reflected in the azimuthal angle between the two hardest jets. This dependence, induced by the $CP$-properties of the Higgs boson couplings, is displayed however, when the sum of jet vectors according to Eq. \ref{['eq:qaqb']} is considered. The lines are fits on the form of Eq. \ref{['eq:fitform']} to the histograms.