Large-$p_\perp$ Heavy-Quark Production in Two-Photon Collisions

TL;DR

The study addresses heavy-quark production at large $p_\perp$ in $\gamma\gamma$ collisions, where fixed-order massive calculations are challenged by $\alpha_s \ln(p_\perp^2/m^2)$ terms. It adopts a massless perturbative fragmentation function (PFF) framework to resum these logarithms, computing NLO differential cross sections for direct and resolved photon processes and comparing with the conventional massive approach across LEP2, NLC (TESLA design), and laser-backscattered photon setups. The results show that the massless and massive schemes yield compatible total cross sections, though their DD/DR/RR decompositions differ; the PFF approach produces a softer $p_\perp$ spectrum and reduced renormalization/factorization scale dependence. This work validates the PFF formalism for reliable predictions of large-$p_\perp$ heavy-quark production in $\gamma\gamma$ collisions and clarifies how direct and resolved contributions map between schemes, with implications for future collider analyses.

Abstract

The next-to-leading-order (NLO) cross section for the production of heavy quarks at large transverse momenta ($p_\perp$) in $γγ$ collisions is calculated with perturbative fragmentation functions (PFF's). This approach allows for a resummation of terms $\proptoα_s\ln(p_\perp^2/m^2)$ which arise in NLO from collinear emission of gluons by heavy quarks at large $p_\perp$ or from almost collinear branching of photons or gluons into heavy-quark pairs. We present single-inclusive distributions in $p_\perp$ and rapidity including direct and resolved photons for $γγ$ production of heavy quarks at $e^+e^-$ colliders and at high-energy $γγ$ colliders. The results are compared with the fixed-order calculation for $m$ finite including QCD radiative corrections. The two approaches differ in the definitions and relative contributions of the direct and resolved terms, but essentially agree in their sum. The resummation of the $α_s \ln(p_\perp^2/m^2)$ terms in the PFF approach leads to a softer $p_\perp$ distribution and to a reduced sensitivity to the choice of the renormalization and factorization scales.