Calculation of prompt diphoton production cross sections at Tevatron and LHC energies

TL;DR

The paper delivers a comprehensive, fully differential calculation of diphoton production at hadron colliders, combining NLO direct contributions with NNLL resummation of initial-state radiation and a careful treatment of final-state fragmentation and photon isolation. It demonstrates good agreement with Tevatron data and provides detailed predictions for LHC kinematics, including comparisons with DIPHOX and implications for Higgs to diphoton searches. The work highlights the necessity of resummation for reliable $Q_T$ distributions, discusses fragmentation modeling under realistic isolation, and offers guidance on cuts (e.g., $Q_T<Q$) to isolate the perturbative core. Overall, it advances precise background predictions for Higgs analyses and clarifies the roles of initial- and final-state radiation in diphoton production.

Abstract

A fully differential calculation in perturbative quantum chromodynamics is presented for the production of massive photon pairs at hadron colliders. All next-to-leading order perturbative contributions from quark-antiquark, gluon-(anti)quark, and gluon-gluon subprocesses are included, as well as all-orders resummation of initial-state gluon radiation valid at next-to-next-to-leading logarithmic accuracy. The region of phase space is specified in which the calculation is most reliable. Good agreement is demonstrated with data from the Fermilab Tevatron, and predictions are made for more detailed tests with CDF and DO data. Predictions are shown for distributions of diphoton pairs produced at the energy of the Large Hadron Collider (LHC). Distributions of the diphoton pairs from the decay of a Higgs boson are contrasted with those produced from QCD processes at the LHC, showing that enhanced sensitivity to the signal can be obtained with judicious selection of events.

Figures (15)

• Figure 1: Representative partonic subprocesses that contribute to continuum diphoton production. All leading-order and next-to-leading order direct production subprocesses, i.e., contributions (a)-(e) and (h)-(l), are included in this study. Diagrams (f) and (g) are examples of single-photon one- and two-fragmentation.
• Figure 2: Lowest-order Feynman diagrams describing fragmentation of the final-state partons into photon pairs with relatively small mass $Q$.
• Figure 3: The diphoton event distribution from the theoretical simulation for $\sqrt{S}=1.96$ GeV, with the selection criteria imposed in the CDF measurement, as a function of the various kinematic variables described in the text, shown for $Q_T < Q$ and $Q_T > Q$ separately.
• Figure 4: Invariant mass distributions of photon pairs in $p\bar{p}\rightarrow\gamma\gamma X$ at $\sqrt{S}=1.96$ TeV with QCD contributions calculated in the soft--gluon resummation formalism (red solid) and at NLO (blue dashed). The calculations include the cuts used by the CDF collaboration whose data are shown Acosta:2004sn.
• Figure 5: Transverse momentum distributions in $p\bar{p}\rightarrow\gamma\gamma X$ at $\sqrt{S}=1.96$ TeV along with the CDF data: (a) the fixed-order prediction $P$ (dashes) and its asymptotic approximation $A$ (dots); (b) the full resummed cross section (solid), obtained by matching the resummed $W+Y$ to the fixed-order prediction $P$ (dashed, same as in (a)) at large $Q_{T}$.