Hadronic $Zγ$ Production with QCD Corrections and Leptonic Decays

TL;DR

The paper delivers a precise NLO QCD calculation of hadronic Zγ production including leptonic Z decays, using a Monte Carlo framework with helicity amplitudes and a narrow width approximation. It reports total and differential cross sections for Tevatron and LHC energies under realistic cuts, highlighting that QCD corrections largely scale invariantly for invariant-mass and angular distributions but enhance high-p_T regions due to real-emission processes, with larger effects at the LHC. The study also analyzes jet components (0-jet vs 1-jet) and shows gluon-dominated dynamics amplify the corrections at higher energies. These results provide realistic predictions for experimental analyses and improve sensitivity to potential new-physics couplings in Zγ production.

Abstract

The process $p p \to Z γ+ X \to \ell^- \ell^+ γ+ X$, where $\ell$ denotes a lepton, is calculated to order $α_s$. Total and differential cross sections, with acceptance cuts imposed on the leptons and photon, are given for the Tevatron and LHC center of mass energies. In general, invariant mass and angular distributions are simply scaled up in magnitude by the QCD radiative corrections, whereas in transverse momentum distributions, the QCD radiative corrections increase with the transverse momentum.

Figures (9)

• Figure 1: Invariant mass distribution of the $\ell^- \ell^+ \gamma$ system for the process $p\,p \hbox{$^{^{(\!-\!)}}$} \rightarrow Z \gamma + X \rightarrow \ell^- \ell^+ \gamma + X$. Parts a) and b) are for the Tevatron and LHC center of mass energies, respectively. The NLO (solid line) and LO (dashed line) cross sections are shown. The cross sections have been summed over $\ell = e, \mu$ and the cuts listed in Sec. IIIB have been imposed.
• Figure 2: Same as Fig. \ref{['FIG:M']} but for the rapidity distribution of the leptons.
• Figure 3: Same as Fig. \ref{['FIG:M']} but for the rapidity distribution of the $Z$ boson.
• Figure 4: The ratio $[d\sigma^{\hbox{\scriptsize NLO}} / dy(\ell)] / [d\sigma^{\hbox{\scriptsize LO}} / dy(\ell)]$ plotted versus $y(\ell)$ for the process $p\,p \hbox{$^{^{(\!-\!)}}$} \rightarrow Z \gamma + X \rightarrow \ell^- \ell^+ \gamma + X$. Parts a) and b) are for the Tevatron and LHC center of mass energies, respectively. The cuts listed in Sec. IIIB have been imposed.
• Figure 5: Same as Fig. \ref{['FIG:M']} but for the angular distribution of the negatively charged lepton. The angle $\theta_{-}$ is measured in the $Z$ boson rest frame with respect to the $Z$ boson direction in the $Z\gamma$ rest frame.