The production cross sections of ${\rm D^0}$ and $\Lambda^+_{\rm c}$ hadrons originating from beauty-hadron decays (i.e. non-prompt) were measured for the first time at midrapidity ($|y|<~0.5$) by the ALICE Collaboration in proton-proton collisions at a center-of-mass energy $\sqrt{s}=13$ TeV. They are described within uncertainties by perturbative QCD calculations employing the fragmentation fractions of beauty quarks to baryons measured at forward rapidity by the LHCb Collaboration. The ${\rm b\overline{b}}$ production cross section per unit of rapidity at midrapidity, estimated from these measurements, is ${\rm d}\sigma_{\rm b\overline{b}}/{\rm d}y|_{|y|<~0.5} = 83.1 \pm 3.5 (\mathrm{stat.}) \pm 5.4(\mathrm{syst.}) ^{+12.3}_{-3.2} (\mathrm{extrap.})\,\mu$b. The baryon-to-meson ratios are computed to investigate the hadronization mechanism of beauty quarks. The non-prompt $\Lambda^+_{\rm c}/{\rm D^0}$ production ratio has a similar trend to the one measured for the promptly produced charmed particles and to the p$/\pi^+$ and $\Lambda/{\rm K^0_S}$ ratios, suggesting a similar baryon-formation mechanism among light, strange, charm, and beauty hadrons. The $p_{\rm T}$-integrated non-prompt $\Lambda_{\rm c}/{\rm D^0}$ ratio is found to be significantly higher than the one measured in e$^+$e$^-$ collisions.
Phys. Rev. D 108, 112003 (2023)
HEP Data
e-Print: arXiv:2308.04873 | PDF | inSPIRE
CERN-EP-2023-159
Figure group
Figure 1
Invariant-mass distributions of the $\Dzero$- and $\Lambda_{\rm c}^+$-hadron candidates and their charge conjugates produced in pp collisions at $\sqrt{s}$ =13 TeV and reconstructed at midrapidity, shown in a selected $\pt$ range. The values for the Gaussian mean $\mu$, width $\sigma$, and raw yield $S$ are reported. Top row: $\Dzero \rightarrow {\rm K^-}\pi^+$ meson candidates measured in the $2 < \pt < 4$ GeV/$c$ interval. Middle row: $\Lambda_{\rm c}^+ \rightarrow {\rm pK^0_S}$ baryon candidates measured in the $2 < \pt < 4$ GeV/$c$ interval. Bottom row: $\Lambda_{\rm c}^+ \rightarrow {\rm pK^-}\pi^+$ baryon candidates measured in the $2 < \pt < 4$ GeV/$c$ interval. The corresponding BDT probability minimum threshold for the candidate selection is reported. The left (right) column corresponds to the prompt (non-prompt) $\Dzero$- and $\Lambda_{\rm c}^+$- hadron candidates enriched sample. |    |
Figure 2
Raw-yield distribution as a function of the BDT-based selection employed in the $\chi^{2}$-minimization procedure adopted for the determination of $f_{\rm nonprompt}$ of $\Dzero$ in $2 < \pt < 4$ GeV/$c$ (top left panel), $\Lambda_{\rm c}^+ \rightarrow {\rm pK^-}\pi^+$ in $4 < \pt < 6$ GeV/$c$ (top right panel), and $\Lambda_{\rm c}^+ \rightarrow {\rm pK^0_S}$ in $6 < \pt < 8$ GeV/$c$ (bottom left panel). Bottom right panel: $f_{\rm nonprompt}$ fraction as function as $\pt$ obtained for the set of selection criteria adopted in the analysis of for non-prompt $\Dzero$, $\Lambda_{\rm c}^+ \rightarrow {\rm pK^-}\pi^+$, and $\Lambda_{\rm c}^+ \rightarrow {\rm pK^0_S}$ hadrons. |  |
Figure 3
$\pt$-differential production cross sections of non-prompt $\Dzero$ and $\Lambda_{\rm c}^+$ hadrons in pp collisions at $\s$=13 TeV compared with predictions obtained with FONLL calculations adopting $f({\rm b \rightarrow B})$ and $f({\rm b \rightarrow }\Lambda^0_{\rm b})$ fragmentation fractions measured in e$^+$e$^-$ collisions and LHCb Collaboration (left panel) and the TAMU model (right panel) combined with PYTHIA8 for the ${\rm h_b \rightarrow h_c+X}$ decay kinematics. |   |
Figure 4
Beauty production cross section per rapidity unit at midrapidity obtained from from dielectron and non-prompt J/$\psi$, $\Dzero$, and $\Lambda_{\rm c}^+$ hadrons measured in pp collisions at $\s$ =13 TeV compared to FONLL and NNLO predictions. The average ${\rm d}\sigma_{\rm b\overline{b}}/{\rm d}y$ of the estimates from the $\Dzero$ and $\Lambda_{\rm c}^+$ hadrons is also reported. |  |
Figure 5
Left: $\pt$-differential ratios of non-prompt $\Lambda_{\rm c}^+$- and $\Dzero$-hadron cross sections compared with predictions obtained with FONLL calculations and PYTHIA8 for the ${\rm h_b \rightarrow h_c+X}$ decay kinematics. The contributions from beauty mesons and from the $\Lambda_{\rm b}^0$ baryon are depicted separately. Right: $\pt$-differential ratios of prompt and non-prompt $\Lambda_{\rm c}^+$- and $\Dzero$-hadron cross sections compared with predictions obtained with the TAMU model and PYTHIA8 for the ${\rm h_b \rightarrow h_c+X}$ decay kinematics. |   |
Figure 6
Non-prompt $\Lambda_{\rm c}^+/\Dzero$, prompt $\Lambda_{\rm c}^+/\Dzero$ , $\Lambda/{\rm K^0_S}$, and p$/\pi^+$ ratios measured in pp collisions at $\s$ = 13 TeV at midrapidity ($|y|<0.5$) compared with the $\Lambda_{\rm b}^0/({\rm B^0 + B^+})$ ratio measured by the LHCb Collaboration at forward rapidity ($2.5< y< 4$) and with predictions obtained with the P YTHIA 8 MC generator with the Monash 2013 tune and the CLR - BLC modes 0, 2, and 3 in the corresponding rapidity range with respect to data. |  |