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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

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 ${\rm D}^0 \to {\rm K}^-\pi^+$, ${\rm D}^+\to {\rm K}^-\pi^+\pi^+$, ${\rm D}^{*+} \to {\rm D}^0 \pi^+ \to {\rm K}^- \pi^+ \pi^+$, ${\rm D^{+}_{s}\to \phi\pi^+\to K^{+} K^{-} \pi^{+}}$, 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.

 

Submitted to: EPJC
e-Print: arXiv:1901.07979 | PDF | inSPIRE

Figures

Figure 1

Invariant-mass (mass-difference) distributions of $\Dzero$, $\Dplus$, $\Dstar$, and $\Ds$ candidates and charge conjugates in $1.5< \pt< 2~\gevc$, $16< \pt< 24~\gevc$, $7< \pt< 7.5~\gevc$, and $3< \pt< 4~\gevc$ 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 $\Dzero$, 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.
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Figure 3

Invariant-mass distributions of $\DtoKpi$ candidates (andcharge conjugates) for $0< \pt< 0.5~\gev/c$. The left panel displaysthe invariant-mass distribution of all ULS K$\pi$ pairs together with thebackground 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 fit function is superimposed.
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Figure 5

Left: examples of fits to the impact-parameter distributions of $\Dzero$ and $\Ds$ 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 $\Dzero$ and $\Ds$-mesons raw yield as a function of $\pt$ 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 $\fprompt$ from the FONLL-based approach are shown by the dashed line and their uncertainty by the red boxes
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Figure 6

Prompt $\Dzero$-meson $\pt$-differential production cross section in $|y|< 0.5$ in pp collisions at $\sqrts =5.02~\tev$ measured with and without decay-vertex reconstruction. The inset shows the ratio of the measurements in their common $\pt$ range. The vertical error bars and the empty boxes represent the statistical and systematic uncertainties, respectively.
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Figure 7

$\pt$-differential production cross section of prompt $\Dzero$, $\Dplus$, $\Dstar$, and $\Ds$ mesons in pp collisionsat $\sqrts=5.02~\tev$. Statistical uncertainties (bars) and systematic uncertainties (boxes) are shown. For the $\Dzero$ meson, the results in $0< \pt< 1~\gev/c$ are obtained from the analysis without decay-vertex reconstruction, while those in \mbox{$1< \pt< 36~\gev/c$} are taken from the analysis with decay-vertex reconstruction. The $\Dstar$-meson cross section is scaled by a factor of 5 for better visibility
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Figure 8

$\pt$-differential production cross sections for prompt $\Dzero$ meson compared to pQCD calculations: FONLL~, GM-VFNS(mod-$\mu_{\rm R,F}$)~, GM-VFNS(SACOT-$m_{\rm T}$)~, and $k_{\rm T}$-factorisation~. The ratios of the data to the theoretical predictions are shown in the lower part of each panel.
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Figure 9

$\pt$-differential production cross sections for prompt $\Dplus$ meson compared to pQCD calculations: FONLL~, GM-VFNS(mod-$\mu_{\rm R,F}$)~, GM-VFNS(SACOT-$m_{\rm T}$)~, and $k_{\rm T}$-factorisation~. The ratios of the data to the theoretical predictions are shown in the lower part of each panel.
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Figure 10

$\pt$-differential production cross sections for prompt $\Dstar$ meson compared to pQCD calculations: FONLL~, GM-VFNS(mod-$\mu_{\rm R,F}$)~, GM-VFNS(SACOT-$m_{\rm T}$)~, and $k_{\rm T}$-factorisation~. The ratios of the data to the theoretical predictions are shown in the lower part of each panel.
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Figure 11

$\pt$-differential production cross sections for prompt $\Ds$ meson compared to GM-VFNS(mod-$\mu_{\rm R,F}$)~, GM-VFNS(SACOT-$m_{\rm T}$)~, and $k_{\rm T}$-factorisation~ pQCD calculations. The ratios of the data to the theoretical predictions are shown in the lower part of each panel.
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Figure 12

Inclusive $\Dzero$ mesons (including also $\Dzero$ mesons from beauty-hadron decays) in $|y|< 0.5$ in pp collisions at $\sqrts =5.02~\tev$, from the analysis without decay-vertex reconstruction, compared to FONLL pQCD calculations~ with the $\mathrm{B} \rightarrow \mathrm{D} + X$ decay kinematics from the EvtGen package~ (grey boxes). The contributions of prompt $\Dzero$ from FONLL (red) and $\Dzero$ from B-meson decays from FONLL+EvtGen (blue) are also shown separately. The vertical error bars and the empty boxes represent the statistical and systematic uncertainties, respectively.
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Figure 13

Ratios of D-meson production cross sections as a function of $\pt$ in pp collisions at $\sqrts=5.02$~TeV and $\sqrts=7$~TeV~.
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Figure 14

Ratios of $\Dzero$, $\Dplus$, $\Dstar$ and $\Ds$-meson production cross sections in pp collisions at $\sqrts=7$~TeV~ and $\sqrts=5.02$~TeV as a function of $\pt$ (left panel). $\Dzero$ ratio compared to FONLL pQCD calculations~ (right panel).
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Figure 15

Ratios of $\Dzero$-meson production cross section per unit of rapidity at mid-rapidity ($|y|< 0.5$) to those measured by the LHCb Collaboration~ in three rapidity ranges, $2< y< 2.5$ (left panel), $3< y< 3.5$ (middle panel), and $4< y< 4.5$ (right panel), as a function of $\pt$ The error bars and boxes represent the statistical and systematic uncertainty, respectively Predictions from FONLL calculations are compared to the data points.
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