Un-integrated PDFs in CCFM

TL;DR

The paper analyzes un-integrated PDFs (uPDFs) derived from CCFM evolution, focusing on their intrinsic transverse momentum distribution at low scales and sensitivity to scale choices. It constructs a starting distribution with Gaussian (and GBW-inspired) $k_t$ inputs, then evolves them with CCFM and off-shell matrix elements, comparing fits to HERA $F_2$ data at small $x$. Key results show the low-$k_t$ region preserves non-perturbative information and possible saturation effects, while large-$k_t$ behavior is dominated by perturbative evolution, with different starting forms converging in the perturbative region. The study also highlights how renormalization and factorization scale choices introduce uncertainties at LO and how the method separates non-perturbative input from perturbative evolution in shaping uPDFs.

Abstract

The un-integrated parton distribution functions (uPDFs) obtained from a CCFM evolution are studied in terms of the intrinsic transverse momentum distribution at low scales. The uPDFs are studied for variations of the renormalization and factorization scales.

Figures (1)

• Figure 1: Comparison of the different sets of un-integrated gluon densities obtained from the CCFM evolution as described in the text.