Measurement of D^0, D^+, D_s^+ and D^{*+} Production in Fixed Target 920 GeV Proton-Nucleus Collisions

TL;DR

The paper presents a comprehensive open-charm study in 920 GeV fixed-target proton-nucleus collisions using HERA-B, delivering total and differential cross sections for $D^0$, $D^+$, $D_s^+$, and $D^{*+}$, along with their $A$-dependence and leading-to-non-leading asymmetries. It employs a detached-vertex strategy and RICH-based PID to extract signals, supported by detailed Monte Carlo efficiency corrections and fits to signal and background. Key outcomes include a per-nucleon charm cross section of about 49 μb, near-unity $A$-dependence, and precise cross-section ratios that align with world averages while offering improved accuracy. These results constrain charm production and hadronization models in hadronic collisions and inform QCD predictions in nuclear environments.

Abstract

The inclusive production cross sections of the charmed mesons D^0, D^+, D_s^+ and D^{*+} have been measured in interactions of 920 GeV protons on C, Ti, and W targets with the HERA-B detector at the HERA storage ring. Differential cross sections as a function of transverse momentum and Feynman's x variable are given for the central rapidity region and for transverse momenta up to $\pT=3.5$ GeV/$c$. The atomic mass number dependence and the leading to non-leading particle production asymmetries are presented as well.

Figures (7)

• Figure 1: A top view of the HERA-B detector.
• Figure 2: Invariant mass distributions for $K^-\pi^+$ (a) and $K^-\pi^+\pi^+$ (b) combinations. The curves show results of maximum likelihood fits to the data.
• Figure 3: Invariant mass distributions for $\phi\pi^+ \to (K^- K^+)\pi^+$ combinations. Besides the $D_s^+$ peak at 1.96 GeV/$c^2$, a $D^+$ peak at 1.87 GeV/$c^2$ is also visible. This peak corresponds to the Cabibbo suppressed decay $D^+ \to \phi \pi^+$. The curve shows the result of a maximum likelihood fit to the data.
• Figure 4: Invariant mass difference $q=m(K,\pi,\pi_{\rm slow})-m(K,\pi)-m_\pi$ for $K^-\pi^+\pi^+$ combinations. The curve shows the result of a maximum likelihood fit to the data.
• Figure 5: Comparison of the present results with previous measurements NA16NA27E743E653E789E769. In figure a) the result of E789 is excluded from the fit. The different curves correspond to different assumptions on parton distribution functions lourenco.