Measurement of charm production at central rapidity in proton-proton collisions at $\sqrt{s} = 7$ TeV

TL;DR

This paper presents the first ALICE measurement of the $p_{ m T}$-differential production cross sections for prompt D mesons (${ m D^0}$, ${ m D^+}$, ${ m D^{*+}}$) at central rapidity in pp collisions at $\sqrt{s}=7$ TeV. Using hadronic decay channels and high-precision tracking and PID in the ALICE central barrel, the analysis extracts yields from invariant-mass distributions, applies feed-down corrections from B decays via FONLL inputs, and computes cross sections with acceptance×efficiency corrections derived from GEANT3-based simulations. The results are compared to perturbative QCD predictions from FONLL and GM-VFNS, showing general agreement within uncertainties and providing constraints on gluon PDFs at small $x$ and on charm hadronization dynamics. The study demonstrates ALICE’s capability to probe charm production in a kinematic regime sensitive to low-$x$ gluon dynamics and potential saturation effects, emphasizing the need for refined saturation-aware calculations.

Abstract

The $p_{\rm T}$-differential inclusive production cross sections of the prompt charmed mesons $D^0$, $D^+$, and $D^{*+}$ in the rapidity range |y|<0.5 were measured in proton-proton collisions at $\sqrt{s} = 7$ TeV at the LHC using the ALICE detector. Reconstructing the decays $D^0\rightarrow K^-π^+$, $D^+\rightarrow K^-π^+π^+$, $D^{*+}\rightarrow D^0π^+$, and their charge conjugates, about 8,400 $D^0$, 2,900 $D^+$, and 2,600 $D^{*+}$ mesons with 1<$p_{\rm T}$<24 GeV/$c$ were counted, after selection cuts, in a data sample of 3.14x10$^8$ events collected with a minimum-bias trigger (integrated luminosity $L_{\rm int}$ = 5/nb). The results are described within uncertainties by predictions based on perturbative QCD.

Figures (5)

• Figure 1: Track impact parameter ($d_0$) resolution in the transverse plane ($r\phi$ direction) as a function of $p_{\rm t}$ comparing data and simulation. This resolution includes the uncertainty in the primary vertex position, which is reconstructed excluding the track being probed.
• Figure 2: Invariant mass distributions for ${\rm D^0}$ (top) and ${\rm D^+}$ (middle) candidates, and mass difference distribution for ${\rm D^{*+}}$ candidates (bottom), for three $p_{\rm t}$ intervals. The curves show the fit functions as described in the text. The values of mean ($\mu$) and width ($\sigma$) of the signal peak are reported (for ${\rm D^0}$ and ${\rm D^+}$ they are expressed in $\mathrm{GeV}/c^2$).
• Figure 3: Acceptance $\times$ efficiency for ${\rm D^0}$, ${\rm D^+}$, and ${\rm D^{*+}}$ mesons, as a function of $p_{\rm t}$ (see text for details).
• Figure 4: Left: prompt fraction $f_{\rm prompt}$ of the ${\rm D^0}$ raw yield as a function of $p_{\rm t}$, for the two FONLL-based methods (solid: central value, from Eq. (\ref{['eq:Nb1']}); dashed: alternative method, from Eq. (\ref{['eq:fc']})) and for the impact parameter fit method (circles); the boxes show the envelope of the uncertainty bands of the two FONLL-based methods; the error bars show the total uncertainty from the impact parameter fit, including the statistical and systematic contributions. Right: an example of ${\rm D^0}$ meson impact parameter distribution in the transverse plane, for $2<p_{\rm t}<3~\mathrm{GeV}/c$; the distribution is background-subtracted and fitted with the two-component function for prompt and feed-down contributions, as described in the text; the resulting prompt fraction, impact parameter resolution for prompt mesons, and $\chi^2$/(number of degrees of freedom) of the fit are given; the inset, with linear scale, shows also the negative entries, resulting from the background subtraction.
• Figure 5: (colour online) $p_{\rm t}$-differential inclusive cross section for prompt ${\rm D^0}$, ${\rm D^+}$, and ${\rm D^{*+}}$ mesons in pp collisions at $\sqrt{s}=7~$TeV compared with FONLL fonllFONLLalice and GM-VFNS gmvfnsDcdfVFNSalice theoretical predictions. The symbols are positioned horizontally at the centre of each $p_{\rm t}$ interval. The normalization uncertainty is not shown (3.5% from the minimum-bias cross section plus the branching ratio uncertainties, as of Table \ref{['tab:Syst']}).