Small-x one-particle-inclusive quantities in the CCFM approach
G. Bottazzi, G. Marchesini, G. P. Salam, M. Scorletti
TL;DR
The paper investigates how to describe small-x DIS data from HERA by employing the CCFM equation to incorporate coherent, angular-ordered gluon radiation beyond DGLAP. It develops a phenomenological framework with an unintegrated gluon density, a chosen CCFM version with a controlled small-x growth, and a fit to F2 to constrain infrared behavior, while computing a set of almost one-particle-inclusive observables. Results show partial improvement over DGLAP-based predictions for some observables (e.g., F2, F2^c, R, energy flow) but with notable discrepancies that undermine detailed phenomenology yet highlight where the approach succeeds and where improvements are needed. The work identifies specific subleading effects, infrared treatment, and scheme choices (e.g., z→0 finite part, non-Sudakov form factor) as critical directions for future refinement, and offers a concrete step toward BFKL-type phenomenology via CCFM while clarifying current limitations and necessary future work.
Abstract
This article presents the results of a quantitative study of the small-x data at HERA, using the CCFM equation. The first step consists of choosing the version of the CCFM equation to be used, corresponding to selecting a particular subset of next-to-leading-logarithmic corrections --- the choice is constrained by requiring a phenomenologically reasonable small-x growth. For the time being, the parts of the splitting functions that are finite at z=0 have been left out. We then examine results for F_2^c, R, the transverse energy flow, the charged-particle transverse-momentum spectrum and the forward-jet cross section and compare to data. While some of the data is reproduced better than with DGLAP-based calculations, the agreement is not entirely satisfactory, suggesting that the approach developed here is not yet suitable for detailed phenomenology. We discuss why, and suggest directions for future work.