Direct Photon Production in Association With A Heavy Quark At Hadron Colliders

TL;DR

The paper delivers a next-to-leading order calculation for direct photon production in association with a heavy quark, including both pointlike photon contributions and photon fragmentation up to $O(α α_s^2)$ and $O(α_s^3)$, respectively, implemented via a two-cutoff phase-space slicing within a variable flavor scheme. It provides detailed predictions for Tevatron and LHC kinematics, examining the evolving dominance of subprocesses (annihilation versus gluon/heavy-quark initiated), the impact of NLO fragmentation and photon isolation, and the role of intrinsic charm in the proton. Key findings show that annihilation dominates at high $p_{Tγ}$ at the Tevatron, while gluon- and heavy-quark-initiated channels dominate at the LHC with a stable $K$-factor around 2, and that isolation substantially reduces fragmentation effects. The work offers a framework to test heavy-quark PDFs and to probe intrinsic charm, contributing to precise Standard Model backgrounds and potential insights for new physics at high-energy colliders.

Abstract

Results of a next-to-leading order calculation of the inclusive cross section for a photon and a heavy quark (charm or bottom), $p \bar p / pp \to γ+Q +X$, are presented. Pointlike photon subprocesses through ${\cal O}(αα_{s}^2)$ and fragmentation subprocesses through ${\cal O}(α_{s}^3)$ are included. The calculation is performed using a phase space slicing technique so that the effects of experimental cuts can be included. Results for the ratios of the charm and bottom cross sections are presented and the systematics of the various subprocesses for both the Tevatron and the LHC are compared and contrasted.

Figures (15)

• Figure 1: Compton Scattering
• Figure 2: An example of Leading Order Fragmentation Contributions 1) $gg \rightarrow Q\bar{Q} \gamma$, where the photon can fragment off from either one of the final state heavy quarks, 2) $gQ\rightarrow gQ \gamma$, where again the photon can fragment off from either one of the final state partons, the gluon or the heavy quark
• Figure 3: An example of Next-to-Leading Order Fragmentation Contributions 1) $gg\rightarrow Q\bar{Q} g \gamma$, where again the photon is produced by fragmenting from either of the final state partons produced in the hard scattering, 2) another example of NLO fragmentation $gQ\rightarrow ggQ \gamma$
• Figure 4: The differential cross section, $d\sigma /dp_{T\gamma}$ for the production of a direct photon and a bottom quark as a function of $p_{T\gamma}$ for $\sqrt{S}=1.96{\rm\ TeV}$, at NLO - solid line, and at LO - dashed line
• Figure 6: Some typical Feynman diagrams for the annihilation subprocess $q\bar{q}\rightarrow \gamma Q\bar{Q}$ where 1) the photon is emitted from the final state heavy quarks and 2) the photon is emitted from the initial state light quarks