The production cross sections of $\mathrm {D^0}$, $\mathrm {D^+}$, and $\mathrm {\Lambda_{c}^{+}}$ hadrons originating from beauty-hadron decays (i.e. non-prompt) were measured for the first time at midrapidity in proton$-$lead (p$-$Pb) collisions at the center-of-mass energy per nucleon pair of $\sqrt{s_{\mathrm{NN}}} = 5.02$ TeV. Nuclear modification factors ($R_{\mathrm {pPb}}$) of non-prompt $\mathrm {D^0}$, $\mathrm {D^+}$, and $\mathrm {\Lambda_{c}^{+}}$ are calculated as a function of the transverse momentum ($p_{\mathrm T}$) to investigate the modification of the momentum spectra measured in p$-$Pb collisions with respect to those measured in proton$-$proton (pp) collisions at the same energy. The $R_{\mathrm {pPb}}$ measurements are compatible with unity and with the measurements in the prompt charm sector, and do not show a significant $p_{\mathrm T}$ dependence. The $p_{\mathrm T}$-integrated cross sections and $p_{\mathrm T}$-integrated $R_{\mathrm {pPb}}$ of non-prompt $\mathrm {D^0}$ and $\mathrm {D^+}$ mesons are also computed by extrapolating the visible cross sections down to $p_{\mathrm T}$ = 0. The non-prompt D-meson $R_{\mathrm {pPb}}$ integrated over $p_{\mathrm T}$ is compatible with unity and with model calculations implementing modification of the parton distribution functions of nucleons bound in nuclei with respect to free nucleons. The non-prompt $\mathrm {\Lambda_{c}^{+}/D^{0}}$ and $\mathrm{D^+/D^0}$ production ratios are computed to investigate hadronisation mechanisms of beauty quarks into mesons and baryons. The measured ratios as a function of $p_{\mathrm T}$ display a similar trend to that measured for charm hadrons in the same collision system.
JHEP 11 (2024) 148
HEP Data
e-Print: arXiv:2407.10593 | PDF | inSPIRE
CERN-EP-2024-193
Figure group
Figure 1
Invariant-mass distributions of $\Dzero$-, $\Dplus$-, and $\Lambda^{+}_{\rm c}$-hadron candidates, and their charge conjugates in selected $\pt$ intervals. The blue solid lines show the total fit functions as described in the text and the red dashed lines show the fit function describing the combinatorial background. For $\Dzero$-meson candidates, the solid green line represents the contribution of the reflections. The mean ($\mu$) and fixed standard deviation ($\sigma$) of the signal fit function, along with the raw-yield ($S$) values, are reported together with their statistical uncertainties resulting from the fit. The fraction of non-prompt candidates in the measured raw yield ($f_{\text{non-prompt}}^{\mathrm{raw}}$) is reported with its statistical and systematic uncertainties. |     |
Figure 3
Left panel: example of raw-yield distribution as a function of the BDT-based selection employed in the data-driven procedure adopted to determine $f_{\text{non-prompt}}^{\mathrm{raw}}$ of $\Dzero$ mesons. Right panel: $f_{\text{non-prompt}}^{\mathrm{raw}}$ fractions as a function of $\pt$ obtained for the set of selection criteria adopted in the analysis for non-prompt $\Dzero$, $\Dplus$, $\Lambda^{+}_{\rm c} \to \mathrm{pK^{-}\pi^{+}}$, and $\Lambda^{+}_{\rm c} \to \mathrm{pK^{0}_{S}}$. The vertical bars and empty boxes represent the statistical and systematic uncertainties, respectively. |   |
Figure 4
$\pt$-differential production cross sections of non-prompt $\Dzero$, $\Dplus$, and $\Lambda^{+}_{\rm c}$ in p-Pb collisions at $\snn = 5.02$ TeV, in comparison with the corresponding production cross section of prompt hadrons from [21, 63]. The measurement of prompt $\Dplus$ mesons is the one reported in [63], with decay BR discussed in the text. The vertical bars and empty boxes represent the statistical and systematic uncertainties (without branching ratio and luminosity contributions), respectively. |    |
Figure 5
Left panel: average $\pt$-differential $R_{\rm pPb}$ of prompt $\Dzero$, $\Dplus$, and $\mathrm{D}^*$ , and non-prompt $\Dzero$ and $\Dplus$ mesons. Right panel: $\pt$-differential $\RpPb$ of prompt and non-prompt $\Lambda^{+}_{\rm c}$ baryons. The vertical bars and empty boxes represent the statistical and systematic uncertainties, respectively. The black-filled box at $\RpPb = 1$ represents the normalisation systematic uncertainty. |   |
Figure 6
Left panel: Nuclear modification factors of non-prompt $\Dzero$ and $\Dplus$ mesons measured in p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV compared with the measurement of non-prompt J/$\psi$ at midrapidity, and the measurements of non-prompt J/$\psi$ and $\rm B^{+}$ mesons at forward and backward rapidity. The results are also compared with B-meson $\RpPb$ calculations using different nPDF sets. Right panel: $\pt$-integrated nuclear modification factor of prompt and non-prompt $\Dzero$ mesons measured in p-Pb and Pb-Pb collisions at $\snn$ = 5.02 TeV. Statistical (bars) and systematic (boxes) uncertainties are shown. Extrapolation uncertainties of non-prompt $\Dzero$ mesons in p-Pb and Pb-Pb collisions are shown separately as shaded bands. |   |
Figure 7
Left panel: prompt (red) and non-prompt (blue) $\Dplus/\Dzero$ yield ratio as a function of $\pt$. Right panel: non-prompt $\Dplus/\Dzero$ yield ratios as a function of $\pt$ measured by ALICE Collaboration in pp (red) and p-Pb (blue) collisions at the same collision energy. The vertical bars and empty boxes represent the statistical and systematic uncertainties (without the branching ratio contribution), respectively. |   |
Figure 8
Top-left panel: non-prompt $\Lambda^{+}_{\rm c} / \Dzero$ yield ratios as a function of $\pt$ measured by ALICE in pp (red) and p-Pb (blue) collisions compared with the $\Lambda^{0}_{\rm b}/\mathrm{B}^{0}$ ratio (green) measured by the LHCb Collaboration at forward rapidity ($2 < y_{\rm lab} < 4.5$) in pp collisions. Top-right panel: prompt (red) and non-prompt (blue) $\Lambda^{+}_{\rm c} / \Dzero$ yield ratios as a function of $\pt$ measured by ALICE in $-0.96 < y_{\rm cms} < 0.04$ together with the $\Lambda_{\mathrm{b}}^0 / \mathrm{B}^0$ yield ratio (green) measured by LHCb in $2.5 < y_{\rm cms} < 3.5$. Bottom panel: ratios of the nuclear modification factor of non-prompt $\Lambda^{+}_{\rm c}$ and non-prompt $\Dzero$ at midrapidity (blue), and the $\Lambda^{0}_{\rm b}$ and $\mathrm{B}^{0}$ at forward and backward rapidity measured by LHCb (red) . |    |