Measurement of ${\rm D^0}$, ${\rm D^+}$, ${\rm D^{*+}}$ and ${{\rm D^+}_s}$ production in pp collisions at $\mathbf{\sqrt{\textit s}~=~5.02~TeV}$ with ALICE

TL;DR

This paper presents a precision measurement of prompt D-meson production (D0, D+, D*+, D_s+) in pp collisions at √s = 5.02 TeV with ALICE, using two complementary analysis approaches to cover a broad pT range and rapidity. The results include pT-differential cross sections, cross-section ratios among D-meson species, and pT-integrated yields, all compared to multiple pQCD frameworks (FONLL, GM-VFNS, kT-factorisation). The measurements provide stringent tests of charm production and fragmentation in QCD at the LHC energy, while delivering essential references for cold and hot nuclear matter studies and constraining gluon PDFs at low x. Overall, the data largely align with pQCD predictions, with some tensions for Ds and in certain pT regions, highlighting areas for theoretical refinement.

Abstract

The measurements of the production of prompt ${\rm D^0}$, ${\rm D^+}$, ${\rm D^{*+}}$, and ${{\rm D^+}_s}$ mesons in proton--proton (pp) collisions at $\sqrt{s}=5.02$ TeV with the ALICE detector at the Large Hadron Collider (LHC) are reported. D mesons were reconstructed at mid-rapidity ($|y|<0.5$) via their hadronic decay channels ${\rm D}^0 \to {\rm K}^-π^+$, ${\rm D}^+\to {\rm K}^-π^+π^+$, ${\rm D}^{*+} \to {\rm D}^0 π^+ \to {\rm K}^- π^+ π^+$, ${\rm D^{+}_{s}\to φπ^+\to K^{+} K^{-} π^{+}}$, and their charge conjugates. The production cross sections were measured in the transverse momentum interval $0<p_{\rm T}<36~\mathrm{GeV}/c$ for ${\rm D^0}$, $1<p_{\rm T}<36~\mathrm{GeV}/c$ for ${\rm D^+}$ and ${\rm D^{*+}}$, and in $2<p_{\rm T}<24~\mathrm{GeV}/c$ for ${{\rm D^+}_s}$ mesons. Thanks to the higher integrated luminosity, an analysis in finer $p_{\rm T}$ bins with respect to the previous measurements at $\sqrt{s}=7$ TeV was performed, allowing for a more detailed description of the cross-section $p_{\rm T}$ shape. The measured $p_{\rm T}$-differential production cross sections are compared to the results at $\sqrt{s}=7$ TeV and to four different perturbative QCD calculations. Its rapidity dependence is also tested combining the ALICE and LHCb measurements in pp collisions at $\sqrt{s}=5.02$ TeV. This measurement will allow for a more accurate determination of the nuclear modification factor in p-Pb and Pb-Pb collisions performed at the same nucleon-nucleon centre-of-mass energy.

Figures (15)

• Figure 1: Invariant-mass (mass-difference) distributions of ${\rm D^0}$, ${\rm D^+}$, ${\rm D^{*+}}$, and ${\rm D^+_s}$ candidates and charge conjugates in $1.5<p_{\rm T}<2~\mathrm{GeV}/c$, $16<p_{\rm T}<24~\mathrm{GeV}/c$, $7<p_{\rm T}<7.5~\mathrm{GeV}/c$, and $3<p_{\rm T}<4~\mathrm{GeV}/c$ intervals, respectively. The blue solid lines show the total fit functions as described in the text and the red dashed lines are the combinatorial-background terms. In case of ${\rm D^0}$, the grey dashed line represents the combinatorial background with the contribution of the reflections. The values of the mean ($\mu$) and the width ($\sigma$) of the signal peak are reported together with the signal counts ($S$) and the signal over background ratio ($S/B$) in the mass interval ($\mu-3\sigma,\mu+3\sigma$). The reported uncertainties are only the statistical uncertainties from the fit.
• Figure 2: Acceptance $\times$ efficiency for ${\rm D^0}$, ${\rm D^+}$, ${\rm D^{*+}}$, and ${\rm D^+_s}$ mesons, as a function of $p_{\rm T}$. The efficiencies for prompt (solid lines) and feed-down (dotted lines) D mesons are shown.
• Figure 3: Invariant-mass distributions of ${\rm D}^0 \to {\rm K}^-\pi^+$ candidates (and charge conjugates) for $0<p_{\rm T}<0.5~\mathrm{GeV}/c$. The left panel displays the invariant-mass distribution of all opposite-sign K$\pi$ pairs (or unlike sign, ULS in the legend) together with the background distribution estimated with the track-rotation technique. The right panel shows the invariant-mass distributions after subtraction of the background from the track-rotation technique. The blue solid line shows the total fit function as described in the text and the grey dashed line is the residual background after the subtraction of the background from the track-rotation technique.
• Figure 4: Product of acceptance and efficiency of ${\rm D}^0 \to {\rm K}^-\pi^+$ (and charge conjugates).
• Figure 5: Left: examples of fits to the impact-parameter distributions of ${\rm D^0}$ and ${\rm D^+_s}$ candidates. The curves show the fit functions describing the prompt, feed-down, and background contributions, as well as their sum, as described in the text. Right: fraction of prompt ${\rm D^0}$ and ${\rm D^+_s}$-mesons raw yield as a function of $p_{\rm T}$ compared to the values obtained with the FONLL-based approach. The results from the data-driven method are shown as square markers with the error bars (boxes) representing the statistical (systematic) uncertainty. The central values of $f_{\rm prompt}$ from the FONLL-based approach are shown by the dashed line and their uncertainty by the red boxes.