Measurement of beauty and charm production in pp collisions at $\sqrt{s}=5.02$ TeV via non-prompt and prompt D mesons

The $p_\mathrm{T}$-differential production cross sections of prompt and non-prompt (produced in beauty-hadron decays) D mesons were measured by the ALICE experiment at midrapidity ($|y|<~0.5$) in proton--proton collisions at $\sqrt{s}=5.02~\mathrm{TeV}$. The data sample used in the analysis corresponds to an integrated luminosity of $(19.3\pm0.4)~\mathrm{nb^{-1}}$. D mesons were reconstructed from their decays $\mathrm{D^0 \to K^-\pi^+}$, $\mathrm{D^+\to K^-\pi^+\pi^+}$, and $\mathrm{D_s^+\to \phi\pi^+\to K^-K^+\pi^+}$ and their charge conjugates. Compared to previous measurements in the same rapidity region, the cross sections of prompt $\mathrm{D^+}$ and $\mathrm{D_s^+}$ mesons have an extended $p_\mathrm{T}$ coverage and total uncertainties reduced by a factor ranging from 1.05 to 1.6, depending on $p_\mathrm{T}$, allowing for a more precise determination of their $p_\mathrm{T}$-integrated cross sections. The results are well described by perturbative QCD calculations. The fragmentation fraction of heavy quarks to strange mesons divided by the one to non-strange mesons, $f_\mathrm{s}/(f_\mathrm{u}+f_\mathrm{d})$, is compatible for charm and beauty quarks and with previous measurements at different centre-of-mass energies and collision systems. The $\mathrm{b\overline{b}}$ production cross section per rapidity unit at midrapidity, estimated from non-prompt D-meson measurements, is $\mathrm{d}\sigma_\mathrm{b\overline{b}}/\mathrm{d} y|_\mathrm{|y|<~0.5} = 34.5 \pm 2.4 (\mathrm{stat.}) ^{+4.7}_{-2.9} (\mathrm{tot. syst.})~\mu\mathrm{b}$. It is compatible with previous measurements at the same centre-of-mass energy and with the cross section predicted by perturbative QCD calculations.

 

JHEP 05 (2021) 220
HEP Data
e-Print: arXiv:2102.13601 | PDF | inSPIRE
CERN-EP-2021-034

Figure 2

Acceptance-times-efficiency factor for $\Dzero$, $\Dplus$, and $\Ds$ mesons as a function of $\pt$. The $(\rm Acc \times \epsilon)$ factors for non-prompt (blue) and prompt (red) D mesons are shown together with their ratio (bottom panels).

Figure 3

Examples of raw-yield distribution as a function of the BDT-based selection employed in the $\chi^2$-minimisation procedure adopted for the determination of $\fnonprompt$ of $\Dzero$ mesons (top left panel), $\Dplus$ mesons (top right panel), and $\Ds$ mesons (bottom left panel) for three different $\pt$ intervals. Bottom right panel, $\fnonprompt$ fraction as a function of $\pt$ obtained for the set of selection criteria adopted in the analysis of non-prompt D mesons.

Figure 5

Comparison of the fractions of prompt $\Dplus$- and $\Ds$-meson raw yields as a function of $\pt$ between the FONLL-based and the data-driven approach. The results from the data-driven method are shown as diamond 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 continuous line and their uncertainty by the shaded boxes.

Figure 6

Left: $\pt$-differential production cross sections of prompt and non-prompt $\Dzero$, $\Dplus$, and $\Ds$ mesons in pp collisions at $\s=5.02~\TeV$. The measurement of prompt $\Dzero$ mesons is the one reported in Ref.~, with updated decay BR as discussed in the text. Right: ratios of $\pt$-differential production cross sections of non-prompt and prompt $\Dzero$, $\Dplus$, and $\Ds$ mesons. Statistical (vertical bars) and systematic uncertainties (boxes) are shown. The symbols are positioned horizontally at the centre of each $\pt$ interval, with the horizontal bars representing the width of the $\pt$ interval.

Figure 7

$\pt$-differential production cross sections of prompt and non-prompt $\Dzero$ (top left panel), $\Dplus$ (top right panel), and $\Ds$ (bottom panel) mesons compared to predictions obtained with FONLL calculations~ combined with PYTHIA~8~ for the $\bhad\to\mathrm{D+X}$ decay kinematics. The measurement of prompt $\Dzero$ mesons is the one reported in Ref.~, with updated decay BR as discussed in the text.

Figure 8

$\pt$-differential production cross sections of prompt and non-prompt $\Dzero$ (top left panel), $\Dplus$ (top right panel), and $\Ds$ (bottom panel) mesons compared to predictions obtained with GM-VFNS calculations~. For the non-prompt $\Dzero$ and $\Dplus$ mesons the one-step (green) and two-step (purple) approaches, describing the transition from the beauty quark to the charm meson, are reported. The measurement of prompt $\Dzero$ mesons is the one reported in Ref.~, with updated decay BR as discussed in the text.

Figure 9

Ratios between the $\pt$-differential production cross sections of $\Dplus$ and $\Dzero$ mesons (left panel) and between the one of $\Ds$ mesons and the sum of the $\Dzero$- and $\Dplus$-meson cross sections (right panel) compared with predictions obtained with FONLL calculations~ and PYTHIA~8~ for the $\bhad\to\mathrm{D+X}$ decay kinematics. For the non-prompt $\Ds/(\Dzero+\Dplus)$ ratio, the predictions for the $\Ds$ from $\Bs$ and from non-strange B meson decays are also displayed separately.

Figure 10

Charm-quark fragmentation-fraction ratio $\f{s}/(\f{u}+\f{d})$ compared with previous measurements performed by the ALICE~, H1~, ZEUS~, and ATLAS~ Collaborations and to the average of LEP measurements~. The total experimental uncertainties (bars) and the theoretical uncertainties (shaded boxes) are shown. The experimental measurements are compared to the value obtained from PYTHIA~8 simulations with Monash-13 tune ~.

Figure 11

Beauty-quark fragmentation-fraction ratio $\f{s}/(\f{u}+\f{d})$ from non-prompt D-meson measurements compared with previous measurements performed by the CDF~, LHCb~, and ATLAS~ Collaborations and to the average of LEP measurements~. The total experimental uncertainties (bars) and the theoretical uncertainties (shaded boxes) are shown. The experimental measurements are compared to the value obtained from PYTHIA~8 simulations with Monash-13 tune ~.

Figure 12

Estimates of $\de\sigma_\bbbar/\de y$ at midrapidity from dielectron~ and non-prompt $\Dzero$, $\Dplus$, and $\Ds$ meson measured in pp collisions at $\s=5.02~\TeV$ compared to FONLL~ and NNLO~ predictions. The average $\de\sigma_\bbbar/\de y$ of the estimates from the single D-meson species is also reported.

Figure 13

Beauty production cross section per rapidity unit at midrapidity as a function of $\s$ as measured in pp collisions by the ALICE~ and PHENIX~ Collaborations and in $\ppbar$ collisions by the CDF~ and UA1~ Collaborations. The ALICE data points are shifted in the $\s$-axis for better visibility. The solid and dashed lines with the shaded band represents the FONLL~ and NNLO~ calculations with their uncertainties, respectively.