Production of D* Mesons with Dijets in Deep-Inelastic Scattering at HERA

TL;DR

This study analyzes $D^{*\pm}$ production in DIS at HERA, including events with dijets, to test perturbative QCD predictions and the gluon content of the proton. It compares NLO calculations in fixed-flavor-number schemes with $k_T$-factorisation predictions, using hadronisation corrections and various PDF inputs. The data largely agree with both approaches within uncertainties, with CASCADE often providing a better description of normalization and forward-region dynamics, and the results disfavor a need for substantial resolved photon contributions beyond NLO. Observables such as $x_{\gamma}^{obs}$ and $x_g^{obs}$ support the validity of gluon densities derived from inclusive DIS fits and demonstrate charm production as a probe of small-$x$ QCD dynamics in DIS.

Abstract

Inclusive D* production is measured in deep-inelastic ep scattering at HERA with the H1 detector. In addition, the production of dijets in events with a D* meson is investigated. The analysis covers values of photon virtuality 2< Q^2 <=100 GeV^2 and of inelasticity 0.05<= y <= 0.7. Differential cross sections are measured as a function of Q^2 and x and of various D* meson and jet observables. Within the experimental and theoretical uncertainties all measured cross sections are found to be adequately described by next-to-leading order (NLO) QCD calculations, based on the photon-gluon fusion process and DGLAP evolution, without the need for an additional resolved component of the photon beyond what is included at NLO. A reasonable description of the data is also achieved by a prediction based on the CCFM evolution of partons involving the k_T-unintegrated gluon distribution of the proton.

Figures (7)

• Figure 1: Differential cross sections for inclusive $D^{*\pm}$ meson production as a function of $Q^2$, $x$, $W$, $p_{\rm T}$, $\eta$ and $z$. The inner error bars indicate the statistical errors, and the outer error bars show the statistical and systematic uncertainties added in quadrature. The bands for the expectations of HVQDIS and CASCADE are obtained using the parameter variations as described in secion 2. Figures a), b) and c) also present the ratio $R=\sigma_{\rm theory} /\sigma_{\text{data}}$ for the predictions as bands, by taking into account their theoretical uncertainties. The inner error bars of the data points at $R=1$ display the relative statistical errors, and the outer error bars show the relative statistical and systematic uncertainties added in quadrature.
• Figure 2: Differential cross sections for inclusive $D^{*\pm}$ meson production with, compared to figure \ref{['fig3a']}, the additional requirement $p_{\rm T}^*>2.0$ GeV for the $D^{*\pm}$ meson in the $\gamma p$ center-of-mass frame as a function of $Q^2$, $x$, $p_{\rm T}$ and $\eta$. The inner error bars indicate the statistical errors, and the outer error bars show the statistical and systematic uncertainties added in quadrature. The bands for the expectations of ZM-VFNS, a "massless" QCD calculation masslesszmfrag and of HVQDIS and CASCADE are obtained using the parameter variations as described in section 2. The ratio R is described in the caption of figure \ref{['fig3a']}.
• Figure 3: Differential cross sections for the production of $D^{*\pm}$ mesons with dijets as a function of $Q^2$, $x$, $E_{\rm T}^{\text{max}}$ in the Breit frame and $M_{\rm jj}$. The inner error bars indicate the statistical errors, and the outer error bars show the statistical and systematic uncertainties added in quadrature. The bands for the expectations of HVQDIS and CASCADE are obtained using the parameter variations as described in section 2. The ratio R is described in the caption of figure \ref{['fig3a']}.
• Figure 4: Double differential cross sections for the production of $D^{*\pm}$ mesons with dijets as a function of $\Delta\phi$ in the Breit frame for two regions in $Q^2$. The inner error bars indicate the statistical errors, and the outer error bars show the statistical and systematic uncertainties added in quadrature. The bands for the expectations of HVQDIS and CASCADE are obtained using the parameter variations as described in section 2. Also shown is the ratio $R_{\text{norm}}^*$, for which the cross section in the last two bins is used for normalisation (for details see section 7).
• Figure 5: Differential cross sections for the production of $D^{*}$-jet and other jet as a function of the pseudorapidity of the $D^*$-jet and the other jet (OJ) and of the difference in pseudorapidity $\Delta\eta=\eta_{\rm DJ} - \eta_{\rm OJ}$ of the two jets. The inner error bars indicate the statistical errors, and the outer error bars show the statistical and systematic uncertainties added in quadrature. The bands for the expectations of HVQDIS and CASCADE are obtained using the parameter variations as described in section 2. In addition, the ratio $R_{\text{norm}}$ is shown (for details see section 7).