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.
Submitted to: JHEP
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 . The measurement of prompt $\Dplus$ mesons is the one reported in [64], 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 $R_{\rm pPb}$ 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 $R_{\rm pPb} = 1$ 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 $R_{\rm pPb}$ 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) . |    |