Measurement of Charm and Beauty Dijet Cross Sections in Photoproduction at HERA using the H1 Vertex Detector

TL;DR

This paper reports measurements of charm and beauty dijet photoproduction cross sections at HERA, using the H1 vertex detector to identify quark flavors and compare results with QCD predictions.

Contribution

It introduces a method based on impact parameter measurements to distinguish charm and beauty quark contributions in dijet events at HERA.

Findings

Charm cross sections agree with NLO QCD calculations.

Beauty cross sections are measured to be higher than theoretical predictions.

Differential cross sections are provided as functions of jet kinematics.

Abstract

A measurement of charm and beauty dijet photoproduction cross sections at the ep collider HERA is presented. Events are selected with two or more jets of transverse momentum $p_t^{jet}_{1(2)}>11(8)$ GeV in the central range of pseudo-rapidity $-0.9<\eta^{jet}_{1(2)}<1.3$. The fractions of events containing charm and beauty quarks are determined using a method based on the impact parameter, in the transverse plane, of tracks to the primary vertex, as measured by the H1 central vertex detector. Differential dijet cross sections for charm and beauty, and their relative contributions to the flavour inclusive dijet photoproduction cross section, are measured as a function of the transverse momentum of the leading jet, the average pseudo-rapidity of the two jets and the observable $x_{\gamma}^{obs}$. Taking into account the theoretical uncertainties, the charm cross sections are consistent with a QCD calculation in next-to-leading order, while the predicted cross sections for beauty production are somewhat lower than the measurement.