CMS-PAS-HIN-18-009

CMS-PAS-HIN-18-009
Production of $\Lambda_C^{+}$ baryons in proton-proton and lead-lead collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}}=$ 5.02 TeV
CMS Collaboration
May 2019

Abstract: The differential cross sections of $\Lambda_C^{+}$ baryon production are measured via the exclusive decay channel $\Lambda_C^{+}\to \mathrm{p} \mathrm{K}^{-}\pi^{+}$ , 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 $\Lambda_C^{+}$ 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 $\Lambda_C^{+}$ for $p_{\mathrm{T}}$ of 10-20 GeV/ $c$ suggest a possible suppression in central PbPb collisions compared to pp collisions. The $\Lambda_C^{+} / D^0$ 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Links: CDS record (PDF) ; CADI line (restricted) ; These preliminary results are superseded in this paper, PLB 803 (2020) 135328. The superseded preliminary plots can be found here.

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Invariant mass distribution of $\Lambda_C^{+}$ 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.
png pdf	Figure 1-a: Invariant mass distribution of $\Lambda_C^{+}$ 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.
png pdf	Figure 1-b: Invariant mass distribution of $\Lambda_C^{+}$ 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.
png pdf	Figure 1-c: Invariant mass distribution of $\Lambda_C^{+}$ 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.
png pdf	Figure 2: The ${p_{\mathrm {T}}}$ -differential cross sections for $\Lambda_C^{+}$ baryon in pp collisions and in three centrality regions of PbPb collisions, along with the PYTHIA8 calculation for pp 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. The lower panel shows the ratio of the measured ${p_{\mathrm {T}}}$ -differential cross section in pp data to the PYTHIA8 calculation. The box at unity in the lower panel indicates the 5.8% normalization uncertainty for pp collision arising from the integrated luminosity and branching fraction. The PbPb normalization uncertainty is included in the systematic uncertainty for each point.
png pdf	Figure 3: The nuclear modification factor $R_\text {AA}$ versus $< N_\text {part} >$ . The boxes and error bars on the data points represent the systematic and statistical uncertainties in the numerator of Eq. (1), respectively. The box at unity indicates the total uncertainty in the pp differential cross section, which is common to all three $R_\text {AA}$ values.
png pdf	Figure 4: The $\Lambda_C^{+} /{\mathrm{D^0}}$ production cross section ratio 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 open crosses and open stars represent the predictions of PYTHIA8 with the CUETP8M1 tune and with color reconnection [34], respectively. The black and pink lines are the calculations from Ref. [29] and Ref. [35], respectively. All predictions are for pp collisions.

Tables
png pdf	Table 1: Summary of the $< N_\text {coll} >$ , $< T_\text {AA} >$ , and $< N_\text {part} >$ values for three PbPb centrality ranges.

Summary

The

${p_{\mathrm{T}}}$ -differential cross sections of

$\Lambda_C^{+}$ 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

$\Lambda_C^{+}$ 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

$\Lambda_C^{+}$ /

${\mathrm{D^0}}$ 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

$\Lambda_C^{+}$ /

${\mathrm{D^0}}$ 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

$\Lambda_C^{+}$ baryon production in this

${p_{\mathrm{T}}}$ range.

References
1	E. V. Shuryak	Theory of Hadronic Plasma	Sov. Phys. JETP 47 (1978) 212.[Zh. Eksp. Teor. Fiz. $\bf74$ (1978) 408]
2	A. Beraudo et al.	Extraction of Heavy-Flavor Transport Coefficients in QCD matter	NP A 979 (2018) 21	1803.03824
3	V. Greco, C. M. Ko, and P. L\'evai	Parton Coalescence and the Antiproton/Pion Anomaly at RHIC	PRL 90 (2003) 202302	nucl-th/0301093
4	STAR Collaboration	Identified baryon and meson distributions at large transverse momenta from Au+Au collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} =$ 200 GeV	PRL 97 (2006) 152301	nucl-ex/0606003
5	STAR Collaboration	Systematic Measurements of Identified Particle Spectra in pp, d+Au and Au+Au Collisions from STAR	PRC 79 (2009) 034909	0808.2041
6	STAR Collaboration	Observation of ${\mathrm{D^0}}$ meson nuclear modifications in $\mathrm{Au}$ + $\mathrm{Au}$ collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} =$ 200 GeV	PRL 113 (2014) 142301	1404.6185
7	Y. Oh, C. M. Ko, S. H. Lee, and S. Yasui	Heavy baryon/meson ratios in relativistic heavy ion collisions	PRC 79 (2009) 044905	0901.1382
8	S. H. Lee et al.	$\Lambda_\text{c}$ enhancement from strongly coupled quark-gluon plasma	PRL 100 (2008) 222301	0709.3637
9	S. Ghosh et al.	Diffusion of $\Lambda_\text{c}$ in hot hadronic medium and its impact on $\Lambda_\text{c}/D$ ratio	PRD 90 (2014) 054018	1407.5069
10	ALICE Collaboration	$\Lambda_\text{c}^+$ production in pp collisions at $\sqrt{s} =$ 7 TeV and in p-Pb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} =$ 5.02 TeV	JHEP 04 (2018) 108	1712.09581
11	ALICE Collaboration	$\Lambda_\text{c}^+$ production in Pb-Pb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} =$ 5.02 TeV	Submitted to: PLB (2018)	1809.10922
12	LHCb Collaboration	Prompt charm production in pp collisions at $\sqrt{s} =$ 7 TeV	NPB 871 (2013) 1	1302.2864
13	LHCb Collaboration	Prompt $\Lambda^+_c$ production in pPb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} =$ 5.02 TeV	JHEP 02 (2019) 102	1809.01404
14	M. A. G. Aivazis, J. C. Collins, F. I. Olness, and W.-K. Tung	Leptoproduction of heavy quarks. II. A unified QCD formulation of charged and neutral current processes from fixed-target to collider energies	PRD 50 (1994) 3102
15	CMS Collaboration	Nuclear modification factor of D $^0$ mesons in PbPb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} =$ 5.02 TeV	PLB 782 (2018) 474	CMS-HIN-16-001 1708.04962
16	CMS Collaboration	The CMS experiment at the CERN LHC	JINST 3 (2008) S08004	CMS-00-001
17	CMS Collaboration	Observation and studies of jet quenching in PbPb collisions at nucleon-nucleon center-of-mass energy = 2.76 TeV	PRC84 (2011) 024906	CMS-HIN-10-004 1102.1957
18	CMS Collaboration	Description and performance of track and primary-vertex reconstruction with the CMS tracker	JINST 9 (2014) P10009	CMS-TRK-11-001 1405.6569
19	CMS Collaboration	Charged-particle nuclear modification factors in PbPb and pPb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} =$ 5.02 TeV	JHEP 04 (2017) 039	CMS-HIN-15-015 1611.01664
20	CMS Collaboration	Description and performance of track and primary-vertex reconstruction with the CMS tracker	JINST 9 (2014) P10009	CMS-TRK-11-001 1405.6569
21	CMS Collaboration	Transverse-momentum and pseudorapidity distributions of charged hadrons in pp collisions at $\sqrt{s} =$ 0.9 and 2.36 TeV	JHEP 02 (2010) 041	CMS-QCD-09-010 1002.0621
22	T. Sjostrand et al.	An introduction to PYTHIA 8.2	CPC 191 (2015) 159	1410.3012
23	CMS Collaboration	Event generator tunes obtained from underlying event and multiparton scattering measurements	EPJC 76 (2016) 155	CMS-GEN-14-001 1512.00815
24	I. P. Lokhtin and A. M. Snigirev	A model of jet quenching in ultrarelativistic heavy ion collisions and high- ${p_{\mathrm{T}}}$ hadron spectra at RHIC	EPJC 45 (2006) 211	hep-ph/0506189
25	D. J. Lange	The EvtGen particle decay simulation package	NIMA 462 (2001) 152
26	GEANT4 Collaboration	GEANT4: a simulation toolkit	NIMA 506 (2003) 250
27	M. L. Miller, K. Reygers, S. J. Sanders, and P. Steinberg	Glauber Modeling in High Energy Nuclear Collisions	Ann. Rev. Nucl. Part. Sci. 57 (2007) 205	nucl-ex/0701025
28	PHENIX Collaboration	Detailed measurement of the $e^+ e^-$ pair continuum in $p+p$ and Au+Au collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} =$ 200 GeV and implications for direct photon production	PRC 81 (2010) 034911	0912.0244
29	S. Plumari et al.	Charmed Hadrons from Coalescence plus Fragmentation in relativistic nucleus-nucleus collisions at RHIC and LHC	EPJC 78 (2018) 348	1712.00730
30	Particle Data Group, M. Tanabashi et al.	Review of Particle Physics	PRD 98 (2018) 030001
31	CMS Collaboration	Measurement of the ${B}^{\pm}$ meson nuclear modification factor in Pb-Pb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} =$ 5.02 TeV	PRL 119 (2017) 152301	CMS-HIN-16-011 1705.04727
32	CMS Collaboration	CMS luminosity calibration for the pp reference run at $\sqrt{s}=$ 5.02 TeV	CMS-PAS-LUM-16-001	CMS-PAS-LUM-16-001
33	P. Skands, S. Carrazza, and J. Rojo	Tuning PYTHIA 8.1: the Monash 2013 Tune	EPJC 74 (2014) 3024	1404.5630
34	J. R. Christiansen and P. Z. Skands	String Formation Beyond Leading Colour	JHEP 08 (2015) 003	1505.01681
35	M. He and R. Rapp	Charm-Baryon Production in Proton-Proton Collisions		1902.08889