Constraining hadronization mechanisms with $\rm Λ_{\rm c}^{+}$/D$^0$ production ratios in Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV

The production of prompt $\rm \Lambda_{\rm c}^{+}$ baryons at midrapidity ($|y|<~0.5$) was measured in central (0-10%) and mid-central (30-50%) Pb-Pb collisions at the center-of-mass energy per nucleon-nucleon pair $\sqrt{s_{\rm NN}} = 5.02$ TeV with the ALICE detector. The results are more precise, more differential in centrality, and reach much lower transverse momentum ($p_{\rm T}=1$ GeV/$c$) with respect to previous measurements performed by the ALICE, STAR, and CMS Collaborations in nucleus-nucleus collisions, allowing for an extrapolation down to $p_{\rm T}=0$. The $p_{\rm T}$-differential $\rm \Lambda_{\rm c}^{+}$/D$^0$ production ratio is enhanced with respect to the pp measurement for $4<~p_{\rm T}<~8$ GeV/$c$ by 3.7 standard deviations ($\sigma$), while the $p_{\rm T}$-integrated ratios are compatible within 1$\sigma$. The observed trend is similar to that observed in the strange sector for the $\Lambda/$K$^0_{\rm S}$ ratio. Model calculations including coalescence or statistical hadronization for charm-hadron formation are compared with the data.

 

Phys. Lett. B 839 (2023) 137796
HEP Data
e-Print: arXiv:2112.08156 | PDF | inSPIRE
CERN-EP-2021-260
Figure group

Figure 1

Left: $p_{\rm T}$-differential production yields of prompt $\Lambda_{\rm c}^+$ in central (0$-$10%) and mid-central (30$-$50%) Pb$-$Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV compared to the pp reference scaled by the $\langle T_{\rm AA} \rangle$ of the corresponding centrality interval. Right: $\Lambda_{\rm c}^+/{\rm D^0}$ ratio in central and mid-central Pb$-$Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV compared with the results obtained from pp collisions.

Figure 2

Nuclear modification factor $R_{\rm AA}$ of prompt $\Lambda_{\rm c}^+$ baryons in central (0$-$10%; left) and mid-central (30$-$50%; right) Pb$-$Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV, compared with the $R_{\rm AA}$ of prompt ${\rm D_s^+}$ and the average of prompt non-strange D mesons. The normalization uncertainties are shown as boxes around unity.

Figure 3

The $\Lambda_{\rm c}^+/{\rm D^0}$ yield ratio as a function of $p_{\rm T}$ in 0$-$10% (left) and 30$-$50% (middle) Pb$-$Pb and pp (right) collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV compared with predictions of different theoretical calculations.

Figure 4

The $p_{\rm T}$-integrated and to $p_{\rm T}>0$ extrapolated $\Lambda_{\rm c}^+/{\rm D^0}$ ratios in central and mid-central Pb$-$Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV compared to the same ratio at pp and p$-$Pb and Au$-$Au multiplicities. Predictions from theoretical calculations are shown as well.

Figure 5

Nuclear modification factor $R_{\rm AA}$ of prompt $\Lambda_{\rm c}^+$ baryons in central (0$-$10%; left) and mid-central (30$-$50%; right) Pb$-$Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV, compared with model predictions. When estimated, the model uncertainty is shown as a shaded band.

Figure A.1

Invariant mass ($M$) distributions of $\Lambda_{\rm c}^+ \rightarrow {\rm pK^0_S} \rightarrow {\rm p}\pi^+\pi^-$ candidates and charge conjugates in different $p_{\rm T}$ intervals in central (0$-$10%; top) and mid-central (30$-$50%; bottom) Pb$-$Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV. The blue solid lines show the total fit functions and the red dashed lines are the combinatorial-background terms. 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 ($\mu-3\sigma,\mu+3\sigma$).