Diphoton production at Tevatron and the LHC in the NLO* approximation of the Parton Reggeization Approach

TL;DR

This work assesses diphoton hadroproduction at high energies within the Parton Reggeization Approach (PRA), integrating k_T-factorization with Reggeized partons and unPDFs to address multi-scale observables beyond conventional collinear QCD. It computes real NLO corrections with a novel mMRK subtraction to prevent double counting and derives the RR\to gamma gamma quark-box amplitude with exact transverse-momentum dependence, including a full numerical treatment and gauge checks. Numerical results show strong agreement with Tevatron and LHC data at high diphoton $p_T$, with the NLO* corrections largely suppressed in the MRK region, while the quark-box contribution remains modest near the $M$ peak. The study demonstrates PRA’s stability and effectiveness for high-energy, multi-scale diphoton production and provides improved background modeling for related resonance searches.

Abstract

The hadroproduction of prompt isolated photon pairs at high energies is studied in the NLO* framework of the Parton Reggeization Approach. The real part of the NLO corrections is computed, and the procedure for the subtraction of double counting between real parton emissions in the hard-scattering matrix element and unintegrated PDF is constructed for the amplitudes with Reggeized quarks in the initial state. The matrix element of the important NNLO subprocess RR->2gamma with full dependence on the transverse momenta of the initial-state Reggeized gluons is obtained. We compare obtained numerical results with diphoton spectra measured at Tevatron and the LHC, and find a good agreement of our predictions with experimental data at the high values of diphoton transverse momentum, pT, and especially at the pT larger than the diphoton invariant mass, M. In this multi-Regge kinematics region, the NLO correction is strongly suppressed, demonstrating the self-consistency of the Parton Reggeization Approach.

Figures (12)

• Figure 1: The Feynman Rules of the effective theory LipatovEFTLipVyaz, relevant for the present study. The propagators, factors, corresponding to the Reggeized quarks (dashed lines with arrows) and gluons (dashed lines) in the initial state of the hard subprocess and necessary interaction vertices are presented. All momenta for the vertices are incoming.
• Figure 2: The set of Feynman diagrams for the LO subprocess (\ref{['proc:QQgaga']}).
• Figure 3: The set of the Feynman diagrams for the NLO subprocess (\ref{['proc:QRgagaq']}).
• Figure 4: The set of the Feynman diagrams for the NLO subprocess (\ref{['proc:QQgagag']}).
• Figure 5: Upper panel, the diagrammatic representation for the squared amplitude of the subprocess (\ref{['proc:QRgagaq']}) and the corresponding mMRK subtraction term. Lower panel -- the same for the subprocess (\ref{['proc:QQgagag']}).