Forward Pi0-Meson Production at HERA

TL;DR

This paper reports measurements of high transverse momentum pi0-mesons produced in deep-inelastic scattering at HERA, providing data sensitive to QCD effects and comparing results with BFKL and DGLAP models.

Contribution

First measurement of forward pi0 production at low Bjorken-x in deep-inelastic scattering, testing QCD models in a new kinematic regime.

Findings

Data agree with DGLAP-based models at higher Q^2

Some discrepancies observed with BFKL predictions in certain regions

Provides new constraints on QCD evolution at low x

Abstract

High transverse momentum pi0-mesons have been measured with the H1 detector at HERA in deep-inelastic ep scattering events at low Bjorken-x, down to x <~ 4.10^{-5}. The measurement is performed in a region of small angles with respect to the proton remnant in the laboratory frame of reference, namely the forward region, and corresponds to central rapidity in the centre of mass system of the virtual photon and proton. This region is expected to be particularly sensitive to QCD effects in hadronic final states. Differential cross-sections for inclusive pi0-meson production are presented as a function of Bjorken-x and the four-momentum transfer Q^2, and as a function of transverse momentum and pseudorapidity. A recent numerical BFKL calculation and predictions from QCD models based on DGLAP parton evolution are compared with the data.