Photon Pair Production with Soft Gluon Resummation in Hadronic Interactions

TL;DR

This work extends the Collins-Soper-Sterman soft-gluon resummation formalism to diphoton production in hadronic collisions, combining q qbar, qg, and gg initiated channels with fragmentation processes to accurately predict the pair's transverse momentum and angular correlations. By matching resummed results to fixed-order calculations and incorporating nonperturbative input, the authors compare to Tevatron data and offer fixed-target predictions, highlighting the significance of gg-initiated contributions and the role of nonperturbative Sudakov effects. The study demonstrates improved agreement with data over fixed-order predictions and discusses the limitations due to approximate treatment of double-initiated gg processes, underscoring the need for a complete O(α_em^2 α_s^3) calculation. It also emphasizes the utility of photon-pair production as a probe of soft-gluon dynamics and a background sigma for Higgs searches, with implications for understanding intrinsic kt and nonperturbative QCD.

Abstract

The production rate and kinematic distributions of isolated photon pairs produced in hadron interactions are studied. The effects of the initial-state multiple soft-gluon emission to the scattering subprocesses q-qbar, qg, and gg to gamma gamma X are resummed with the Collins-Soper-Sterman soft gluon resummation formalism. The effects of fragmentation photons from qg to gamma q, followed by q to gamma X, are also studied. The results are compared with data from the Fermilab Tevatron collider. A prediction of the production rate and kinematic distributions of the diphoton pair in proton-nucleon reactions is also presented.

Figures (14)

• Figure 1: Feynman diagrams representing the leading order and next--to--leading order contributions to photon pair production in hadron collisions. The shaded circles signify the production of long--distance fragmentation photons, which are described by the fragmentation function $D_{\gamma\leftarrow q}$.
• Figure 2: Comparison of the parton--level and Monte Carlo fragmentation contributions at the Tevatron. The upper and lower curves of the same type show the contribution before and after an isolation cut. The left figure shows the transverse momentum of the photon pair $Q_T$. The right figure shows the light--cone momentum fraction carried by the fragmentation photon.
• Figure 3: The predicted distribution for the invariant mass of the photon pair $M_{\gamma\gamma}$ from the resummed calculation compared to the CDF data, with the CDF cuts imposed in the calculation.
• Figure 4: The predicted distribution for the transverse momentum of the photon pair $Q_{T}$ from the resummed calculation compared to the CDF data, with the CDF cuts imposed in the calculation.
• Figure 5: The predicted distribution for the difference between the azimuthal angles of the photons $\Delta\phi_{\gamma\gamma}$ from the resummed calculation compared to the CDF data, with the CDF cuts imposed in the calculation.