Status of CCFM - unintegrated gluon densities

TL;DR

This work updates the CCFM framework to obtain unintegrated gluon densities for the proton and extends it to the real photon. It introduces updated splitting-function treatments, investigates soft-region cutoffs and scale choices, and presents three J2003 proton sets fitted to HERA $F_2(x,Q^2)$ data, with comparisons to the previous JS solution. The photon case uses CASCADE with a GRVgam-based photon density to predict heavy-quark production in $\gamma\gamma$ collisions, finding reasonable charm agreement but underprediction for bottom, and comparing $k_\perp$-factorization to NLO. Overall, the results improve the understanding of small-$x$ gluon densities and enable more reliable predictions for photon-induced processes.

Abstract

New fits of the unintegrated gluon density obtained from CCFM evolution to HERA $F_2(x,Q^2)$ data are presented. Also predictions of the unintegrated gluon density of the real photon are presented.

Figures (2)

• Figure 1: Comparison of the different sets of unintegrated gluon densities obtained from the CCFM evolution as described in the text. In $(a-c)$ the unintegrated gluon density is shown as a function of $x$ for different values of $k_\perp$ at a scale of $\bar{q}=10$ GeV. In $(d-f)$ the ratio $R=\frac{x{\@fontswitch\mathcal{A}}(x,k_\perp^2,\bar{q}^2)}{x{\@fontswitch\mathcal{A}}(x,k_\perp^2,\bar{q}^2)_{\bf JS}}$ as a function of $x$ for different values of $k_\perp$ is shown.
• Figure 2: The cross section for heavy quark production obtained with Cascade using the CCFM unintegrated gluon density of the photon compared to measurements in $\gamma \gamma$ collisions.