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| CMS-HIN-18-009 ; CERN-EP-2019-102 | ||
| Production of $\Lambda_{\mathrm{c}}^{+}$ baryons in proton-proton and lead-lead collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} = $ 5.02 TeV | ||
| CMS Collaboration | ||
| 7 June 2019 | ||
| Phys. Lett. B 803 (2020) 135328 | ||
| Abstract: The differential cross sections of $\Lambda_{\mathrm{c}}^{+}$ baryon production are measured via the exclusive decay channel ${\Lambda_{\mathrm{c}}^{+}\to{\mathrm{p}}\mathrm{K^{-}}\pi^{+}} $, as a function of transverse momentum (${p_{\mathrm{T}}}$) in proton-proton (pp) and lead-lead (PbPb) collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV with the CMS detector at the LHC. The measurement is performed within the $\Lambda_{\mathrm{c}}^{+}$ rapidity interval $| y | < $ 1.0 in the ${p_{\mathrm{T}}}$ range of 5-20 GeV/$c$ in pp and 10-20 GeV/$c$ in PbPb collisions. The observed yields of $\Lambda_{\mathrm{c}}^{+}$ for ${p_{\mathrm{T}}}$ of 10-20 GeV/$c$ suggest a possible suppression in central PbPb collisions compared to pp collisions. The ${\Lambda_{\mathrm{c}}^{+}/ {\mathrm{D^0}}} $ production ratio in pp collisions is compared to theoretical models. In PbPb collisions, this ratio is consistent with the result from pp collisions in their common ${p_{\mathrm{T}}}$ range. | ||
| Links: e-print arXiv:1906.03322 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Invariant mass distribution of $\Lambda_{\mathrm{c}}^{+} $ candidates with $ {p_{\mathrm {T}}} = $ 5-6 GeV/$c$ (left), 10-20 GeV/$c$ (middle) in pp collisions, and $ {p_{\mathrm {T}}} = $ 10-20 GeV/$c$ in PbPb collisions within the centrality range 0-100% (right). The solid line represents the full fit and the dashed line represents the background component. |
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Figure 1-a:
Invariant mass distribution of $\Lambda_{\mathrm{c}}^{+} $ candidates with $ {p_{\mathrm {T}}} = $ 5-6 GeV/$c$ in pp collisions. The solid line represents the full fit and the dashed line represents the background component. |
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Figure 1-b:
Invariant mass distribution of $\Lambda_{\mathrm{c}}^{+} $ candidates with $ {p_{\mathrm {T}}} = $ 10-20 GeV/$c$ in pp collisions. The solid line represents the full fit and the dashed line represents the background component. |
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Figure 1-c:
Invariant mass distribution of $\Lambda_{\mathrm{c}}^{+} $ candidates with $ {p_{\mathrm {T}}} = $ 10-20 GeV/$c$ in PbPb collisions within the centrality range 0-100%. The solid line represents the full fit and the dashed line represents the background component. |
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Figure 2:
The ${p_{\mathrm {T}}} $-differential cross sections for inclusive $\Lambda_{\mathrm{c}}^{+} $ production in pp collisions and the $T_\text {AA}$-scaled yields for three centrality regions of PbPb collisions. The boxes and error bars represent the systematic and statistical uncertainties, respectively. The PbPb data points are shifted in the horizontal axis for clarity. Predictions for pp collisions are displayed for PYTHIA 8 with the CUETP8M1 tune (open crosses), PYTHIA 8 with color reconnection [43] (open stars), and GM-VFNS [44] (open circles labeled "JHEP 12 (2017) 021'') along with ratios to the data in the lower two panels. The PYTHIA 8 (GM-VFNS) predictions are for inclusive (prompt) $\Lambda_{\mathrm{c}}^{+} $ production. The error bars on the GM-VFNS prediction account for the scale variation uncertainty. The lower panels show the data-to-prediction ratio for pp collisions with inner and outer error bars corresponding to the statistical and total uncertainty in the data, respectively, and the shaded box at unity indicating the 21% normalization uncertainty. The shaded boxes in the bottom panel represent the GM-VFNS uncertainty. |
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Figure 3:
The nuclear modification factor $ {R_{\mathrm {AA}}} $ versus $< {N_\text {part}} > $ for inclusive $\Lambda_{\mathrm{c}}^{+} $ production. The error bars represent the PbPb yield statistical uncertainties. The boxes at each point include the PbPb systematic uncertainties associated with the signal extraction, $ {p_{\mathrm {T}}} $ spectrum, selection criteria, track reconstruction, and ${T_{\mathrm {AA}}}$. The band at unity labeled pp uncertainty includes these same uncertainties for the pp data (except for ${T_{\mathrm {AA}}}$) plus the uncertainties in pp yield and luminosity. The band at unity labeled PbPb includes the uncertainty from the nonprompt fraction (accounting for a partial cancelation between pp and PbPb) and MB selection efficiency. |
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Figure 4:
The ratio of the production cross sections of inclusive $\Lambda_{\mathrm{c}}^{+} $ to prompt ${\mathrm{D^0}} $ versus ${p_{\mathrm {T}}}$ from pp collisions as well as 0-100% centrality PbPb collisions. The boxes and error bars represent the systematic and statistical uncertainties, respectively. The PbPb data point is shifted in the horizontal axis for clarity. The 20 and 31% normalization uncertainties in pp and PbPb collisions, respectively, are not included in the boxes representing the systematic uncertainties for each data point. The open crosses and open stars represent the predictions of PYTHIA 8 with the CUETP8M1 tune and with color reconnection [43], respectively. The solid and dashed lines are the calculations for prompt $\Lambda_{\mathrm{c}}^{+} $ over prompt ${\mathrm{D^0}} $ production ratio from Ref. [20] and Ref. [46], respectively. All predictions are for pp collisions. |
| Tables | |
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Table 1:
Summary of the $< {N_\text {coll}} > $, $< {T_{\mathrm {AA}}} > $, and $< {N_\text {part}} > $ values for three PbPb centrality ranges. |
| Summary |
| The ${p_{\mathrm{T}}}$-differential cross sections of $\Lambda_{\mathrm{c}}^{+}$ baryons have been measured in pp and PbPb collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV. The shape of the ${p_{\mathrm{T}}}$ distribution in pp collisions is well described by the PYTHIA8 event generator. A hint of suppression of $\Lambda_{\mathrm{c}}^{+}$ production for 10 $ < {p_{\mathrm{T}}} < $ 20 GeV/$c$ is observed in PbPb when compared to pp data, with central PbPb events showing stronger suppression. This possible suppression may originate from the strong interaction between the charm quark and the quark-gluon plasma medium, as previously indicated by the ${\mathrm{D^0}}$ meson measurements. The ${\Lambda_{\mathrm{c}}^{+}/ {\mathrm{D^0}}} $ production ratios in pp collisions are consistent with a model obtained by adding color reconnection in hadronization to PYTHIA8, and also with a model that includes enhanced contributions from the decay of excited charm baryons. A model including coalescence underpredicts the data for ${p_{\mathrm{T}}}$ above about 8-10 GeV/$c$. The ${\Lambda_{\mathrm{c}}^{+}/ {\mathrm{D^0}}} $ production ratios in pp and PbPb collisions for ${p_{\mathrm{T}}}= $ 10-20 GeV/$c$ are found to be consistent with each other. These two observations may suggest that the coalescence process does not play a significant role in $\Lambda_{\mathrm{c}}^{+}$ baryon production in this ${p_{\mathrm{T}}}$ range. |
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