Forward pi^0-meson production at HERA

TL;DR

This paper reports the first measurements of high transverse momentum pi^0-mesons produced in deep-inelastic e-p scattering at low Bjorken-x, extending into the forward region and comparing results with QCD models, notably favoring BFKL predictions.

Contribution

It provides the first measurement of single pi^0-mesons in the forward region at very low x, testing QCD evolution models against experimental data.

Findings

BFKL calculation best describes the data

Extended measurements into the forward region at low x

Differential cross sections measured as functions of x, Q^2, p_T, and angle

Abstract

The production of high transverse momentum piz^0-mesons has been measured in deep-inelastic e-p scattering events at low Bjorken-$x$ taken with the H1 detector at HERA. The production of high p_T particles is strongly correlated to the emission of hard partons in QCD and is therefore sensitive to the dynamics of the strong interaction. For the first time the measurement of single particles has been extended to the region of small angles w.r.t. the proton remnant (forward region) and down to very low values of x ~ 5x10^-5. This region is expected to be particularly sensitive to QCD evolution effects in final states. Differential cross sections of inclusive pi^0-meson production have been measured as a function of Bjorken-x and the four-momentum transfer Q^2, and also as a function of the transverse momentum and the polar angle of the pi^0-mesons. A recent BFKL calculation and QCD models based on the DGLAP splitting functions are compared to the data. The best description of the data is achieved by the BFKL calculation.