Inclusive Production of D^+, D^0, D_s^+ and D^*+ Mesons in Deep Inelastic Scattering at HERA

TL;DR

This study measures inclusive production cross sections for $D^+$, $D^0$, $D_s^+$ and $D^{*+}$ in deep inelastic $ep$ scattering at HERA to test the universality of charm fragmentation. By reconstructing displaced decay vertices with the H1 CST, the analysis compares data to LO AROMA and NLO HVQDIS predictions and extracts fragmentation factors and ratios. The results show similar differential cross sections across the four mesons and fragmentation factors in agreement with world averages, supporting the factorisation of charm production and universal hadronisation. Overall, the findings reinforce that charm quark production and fragmentation in DIS can be described by perturbative QCD with a universal fragmentation function, consistent with $e^+e^-$ data.

Abstract

Inclusive production cross sections are measured in deep inelastic scattering at HERA for meson states composed of a charm quark and a light antiquark or the charge conjugate. The measurements cover the kinematic region of photon virtuality 2 < Q^2 < 100 GeV^2, inelasticity 0.05 < y < 0.7, D meson transverse momenta p_t(D) > 2.5 GeV and pseudorapidity |eta(D)| < 1.5. The identification of the D-meson decays and the reduction of the combinatorial background profit from the reconstruction of displaced secondary vertices by means of the H1 silicon vertex detector. The production of charmed mesons containing the light quarks u, d and s is found to be compatible with a description in which the hard scattering is followed by a factorisable and universal hadronisation process.

Figures (6)

• Figure 1: Diagram for the production of $c$-quarks in $ep$ collisions via the photon-gluon fusion process. The hadronisation into a charmed meson $D$ is described by the fragmentation function $D_D^{(c)}(z)$ (cf. Eq. \ref{['eq:f3']}).
• Figure 2: a) Invariant mass distribution $m(K\pi)$ and b) signed decay length significance distribution $S_l$ measured for tagged $D^{0}$ mesons in data (solid points). Superimposed is the fitted decomposition into signal ($S$, hatched) and background ($B$, shaded) contributions (see text). The background in b) is determined from the $m(K\pi)$ sideband regions $(sb)$ as indicated in a).
• Figure 3: Invariant mass distributions $m(K \pi \pi)$ for $D^+ \rightarrow K^- \pi^+ \pi^+$ decay candidates (a) before and (b) after a cut on the decay length significance $S_l> 8$.
• Figure 4: Invariant mass distributions for the four $D$ meson candidate decays that are used to determine the number of signal events: a) $D^+ \to K^- \pi^+ \pi^+$, b) $D^{0} \to K^- \pi^+$, c) $D^{+}_s \to \phi \pi^+ \to K^+ K^- \pi^+$ and d) $D^{*+} \to D^{0} \pi^+_s \to K^- \pi^+ \pi^+_s$ ( the invariant mass $m(K \pi)$ is shown after the $\Delta m$ cut). The curves show the fits in which the signals are described by a Gaussian and the backgrounds are parametrised as discussed in the text.
• Figure 5: Differential production cross section for $D^+$ as a function of a) the $D^+$ transverse momentum $p_t(D^+)$, b) the pseudorapidity $\eta(D^+)$, c) the photon virtuality $Q^2$, and d) the inelasticity $y$. The symbols denote the values averaged over the bins and are plotted at the bin centres. The error bars show the statistical (inner bars) and the total (outer bars) errors, respectively. The solid lines show the LO AROMA predictions including scaled beauty contributions, shown separately as dashed lines. The shaded bands indicate the uncertainties on the predictions (see text).