Rivet analyses referenceALICE_2017_I1645239$\Lambda_\mathrm{c}^+$ production in pp collisions at $\sqrt{s} = 7$ TeV and in p-Pb collisions at $\sqrt{s_\mathrm{NN}} = 5.02$ TeVExperiment: ALICE (LHC) Inspire ID: 1645239 Status: VALIDATED Authors:
The $p_{T}$-differential production cross section of prompt $\Lambda_{c}^{+}$ charmed baryons was measured with the ALICE detector at the Large Hadron Collider (LHC) in pp collisions at $ \sqrt{s}=7 $ TeV and in p-Pb collisions at $ \sqrt{s_{\mathrm{NN}}}=5.02 $ TeV at midrapidity. The $\Lambda_{c}^{+}$ and $ {\overline{\varLambda}}_{\overline{\mathrm{c}}} $ were reconstructed in the hadronic decay modes $\Lambda_{c}^{+} \to$ pK$^{-} \pi^{+}$, $\Lambda_{c}^{+} \to$ pK$_{S}^{0}$ and in the semileptonic channel $\Lambda_{c}^{+} \to$ e$^{+}\nu_{e} \Lambda$ (and charge conjugates). The measured values of the $\Lambda_{c}^{+}$ /D$^{0}$ ratio, which is sensitive to the c-quark hadronisation mechanism, and in particular to the production of baryons, are presented and are larger than those measured previously in different colliding systems, centre-of-mass energies, rapidity and $p_{T}$ intervals, where the $\Lambda_{c}^{+}$ production process may differ. The results are compared with the expectations obtained from perturbative Quantum Chromodynamics calculations and Monte Carlo event generators. Neither perturbative QCD calculations nor Monte Carlo models reproduce the data, indicating that the fragmentation of heavy-flavour baryons is not well understood. The first measurement at the LHC of the $\Lambda_{c}^{+}$ nuclear modification factor, $R_{pPb}$, is also presented. The $R_{pPb}$ is found to be consistent with unity and with that of D mesons within the uncertainties, and consistent with a theoretical calculation that includes cold nuclear matter effects and a calculation that includes charm quark interactions with a deconfined medium. Source code: ALICE_2017_I1645239.cc 1// -*- C++ -*-
2#include "Rivet/Analysis.hh"
3#include "Rivet/Projections/FastJets.hh"
4#include "Rivet/Projections/FinalState.hh"
5#include "Rivet/Projections/UnstableParticles.hh"
6
7namespace Rivet {
8
9
10 /// Lambda_c production in pp collisions at 7 TeV and in p-Pb collisions at sqrt{sNN} = 5.02 TeV
11 class ALICE_2017_I1645239 : public Analysis {
12 public:
13
14 /// Constructor
15 RIVET_DEFAULT_ANALYSIS_CTOR(ALICE_2017_I1645239);
16
17
18 /// @name Analysis methods
19 /// @{
20
21 /// Book histograms and initialise projections before the run
22 void init() {
23 // Initialise and register projections
24 declare(UnstableParticles(Cuts::absrap < 0.96), "upProj");
25
26 // Book histograms
27 book(_h_Lc, 1, 1, 1); // Lc in pp at 7 TeV
28 book(_h_LcPb, 2, 1, 1); // Lc in p-Pb at 5.02 TeV
29 book(_h_LcD0, 3, 1, 1); // Lc/D0 in pp at 7 TeV
30 book(_h_LcD0Pb, 4, 1, 1); // Lc/D0 in p-Pb at 5.02 TeV
31 book(_h_LcD0int, 5, 1, 1); // "Integrated" Lc/D0 in pp at 7 TeV (1 < pT < 8 GeV/c)
32 book(_h_LcD0Pbint, 6, 1, 1); // "Integrated" Lc/D0 in p-Pb at 5.02 TeV (2 < pT < 12 GeV/c)
33 book(_h_RpPb, 7, 1, 1); // RpPb
34 book(_h_Lcdummy, "TMP/Lcdummy", refData(3, 1, 1)); // Lc in pp at 7 TeV with (_h_LcD0) binning
35 book(_h_D0, "TMP/D0", refData(3, 1, 1)); // D0 in pp at 7 TeV with (_h_LcD0) binning
36 book(_h_LcPbdummy, "TMP/LcPbdummy", refData(4, 1, 1)); // Lc in p-Pb at 5.02 TeV with (_h_LcD0Pb) binning
37 book(_h_D0Pb, "TMP/D0Pb", refData(4, 1, 1)); // D0 in p-Pb at 5.02 TeV with (_h_LcD0Pb) binning
38 book(_h_Lcint, "TMP/Lcint", refData(5, 1, 1)); // "Integrated" Lc in pp at 7 TeV with (_h_LcD0int) binning
39 book(_h_D0int, "TMP/D0int", refData(5, 1, 1)); // "Integrated" D0 in pp at 7 TeV with (_h_LcD0int) binning
40 book(_h_LcintPb, "TMP/LcintPb", refData(6, 1, 1)); // "Integrated" Lc in p-Pb at 5.02 TeV with (_h_LcD0Pbint) binning
41 book(_h_D0intPb, "TMP/D0intPb", refData(6, 1, 1)); // "Integrated" D0 in p-Pb at 5.02 TeV with (_h_LcD0Pbint) binning
42 book(_h_LcR, "TMP/LcR", refData(7, 1, 1)); // Lc in pp at 5.02 TeV with (_h_RpPb) binning
43 book(_h_LcRPb, "TMP/LcRPb", refData(7, 1, 1)); // Lc in p-Pb at 5.02 TeV with (_h_RpPb) binning
44 }
45
46
47 /// Perform the per-event analysis
48 void analyze(const Event& event) {
49 PdgIdPair beamp = beamIDs();
50 const UnstableParticles& upProj = apply<UnstableParticles>(event, "upProj");
51
52 // PDG code IDs used in the code: 2212 = p+, 4122 = Lc, 421 = D0, 1000822080 = Pb
53 if (beamp.first == PID::PROTON && beamp.second == PID::PROTON) {
54 // pp cycle
55 if (isCompatibleWithSqrtS(5020*GeV)) { // pp 5.02 TeV
56 for (const Particle& p : upProj.particles()) {
57 if (p.fromBottom()) continue;
58 if (p.rap() < 0.04 && p.rap() > -0.96) {
59 // NOTE : when building the Lc reference at 5.02 TeV in pp, we
60 // use directly here the rapidity range covered in p-Pb In the
61 // absence of real data Lc pp 5.02 TeV, the ALICE publication
62 // uses an FONLL-based extrapolation from Lc pp data : i) at
63 // sqrt(s) = 7 TeV ii) in |y| < 0.5, with dedicated systematic
64 // uncertainties due this choice.
65 if (p.abspid() == 4122) _h_LcR->fill(p.pT() / GeV);
66 }
67 }
68 } else { // pp 7 TeV
69 for (const Particle& p : upProj.particles()) {
70 if (p.fromBottom()) continue;
71 if (p.absrap() < 0.5) {
72 if (p.abspid() == 421) {
73 _h_D0->fill(p.pT() / GeV);
74 _h_D0int->fill(0);
75 } // end if D0
76 else if (p.abspid() == 4122) {
77 _h_Lc->fill(p.pT() / GeV);
78 _h_Lcdummy->fill(p.pT() / GeV);
79 _h_Lcint->fill(0);
80 } // end if Lc
81 } // end if |y| < 0.5
82 }
83 }
84 } // end if pp beams
85 else if ((beamp.first == 2212 && beamp.second == 1000822080) || (beamp.second == 2212 && beamp.first == 1000822080)) {
86 // p-Pb cycle at 5.02 TeV
87 for (const Particle& p : upProj.particles()) {
88 if (p.fromBottom()) continue;
89 if (p.rap() < 0.04 && p.rap() > -0.96) {
90 if (p.abspid() == 421) {
91 _h_D0Pb->fill(p.pT() / GeV);
92 _h_D0intPb->fill(-0.5);
93 } // end if D0
94 else if (p.abspid() == 4122) {
95 _h_LcPb->fill(p.pT() / GeV);
96 _h_LcPbdummy->fill(p.pT() / GeV);
97 _h_LcRPb->fill(p.pT() / GeV);
98 _h_LcintPb->fill(-0.5);
99 } // if Lc
100 } // end if -0.96 < y< 0.04
101 }
102 } // end p-Pb
103 }
104
105
106 /// Normalise histograms etc., after the run
107 void finalize() {
108 // NOTE 1 : At this point cross sections consider both particles and
109 // antiparticles, hence a factor 2 is added in the histos normalization
110 // in order to account for this (as done in the paper) NOTE 2 : any
111 // rapidity range here is 1-unit wide (in pp and p-Pb), no further
112 // division by 1 is requested to get dsigma/dpTdy cross section
113 if (_h_D0->numEntries() > 0) scale(_h_D0, crossSection() / (microbarn * 2 * sumOfWeights())); // norm to cross section
114 if (_h_D0int->numEntries() > 0) scale(_h_D0int, crossSection() / (microbarn * 2 * sumOfWeights())); // norm to cross section
115 if (_h_Lc->numEntries() > 0) scale(_h_Lc, crossSection() / (microbarn * 2 * sumOfWeights())); // norm to cross section
116 if (_h_Lcdummy->numEntries() > 0) scale(_h_Lcdummy, crossSection() / (microbarn * 2 * sumOfWeights())); // norm to cross section
117 if (_h_LcPbdummy->numEntries() > 0) scale(_h_LcPbdummy, crossSection() / (microbarn * 2 * sumOfWeights())); // norm to cross section
118 if (_h_Lcint->numEntries() > 0) scale(_h_Lcint, crossSection() / (microbarn * 2 * sumOfWeights())); // norm to cross section
119 if (_h_D0Pb->numEntries() > 0) scale(_h_D0Pb, crossSection() / (microbarn * 2 * sumOfWeights())); // norm to cross section
120 if (_h_D0intPb->numEntries() > 0) scale(_h_D0intPb, crossSection() / (microbarn * 2 * sumOfWeights())); // norm to cross section
121 if (_h_LcPb->numEntries() > 0) scale(_h_LcPb, crossSection() / (microbarn * 2 * sumOfWeights())); // norm to cross section
122 if (_h_LcintPb->numEntries() > 0) scale(_h_LcintPb, crossSection() / (microbarn * 2 * sumOfWeights())); // norm to cross section
123
124 if (_h_Lcdummy->numEntries() > 0 && _h_D0->numEntries() > 0) divide(_h_Lcdummy, _h_D0, _h_LcD0);
125 if (_h_LcPbdummy->numEntries() > 0 && _h_D0Pb->numEntries() > 0) divide(_h_LcPbdummy, _h_D0Pb, _h_LcD0Pb);
126 if (_h_Lcint->numEntries() > 0 && _h_D0int->numEntries() > 0) divide(_h_Lcint, _h_D0int, _h_LcD0int);
127 if (_h_LcintPb->numEntries() > 0 && _h_D0intPb->numEntries() > 0) divide(_h_LcintPb, _h_D0intPb, _h_LcD0Pbint);
128
129 if (_h_LcR->numEntries() > 0) scale(_h_LcR, 208 * crossSection() / (microbarn * 2 * sumOfWeights())); // norm to cross section, 208 is Z_Pb
130 if (_h_LcRPb->numEntries() > 0) scale(_h_LcRPb, crossSection() / (microbarn * 2 * sumOfWeights())); // norm to cross section
131 if (_h_LcRPb->numEntries() > 0 && _h_LcR->numEntries() > 0) divide(_h_LcRPb, _h_LcR, _h_RpPb);
132 }
133
134 /// @}
135
136
137 /// @name Histograms
138 /// @{
139 Histo1DPtr _h_Lc, _h_LcPb, _h_D0, _h_D0Pb, _h_Lcint, _h_LcintPb, _h_D0int, _h_D0intPb, _h_LcR, _h_LcRPb, _h_Lcdummy,_h_LcPbdummy;
140 Estimate1DPtr _h_LcD0, _h_LcD0Pb, _h_LcD0int, _h_LcD0Pbint, _h_RpPb;
141 /// @}
142
143 };
144
145
146 RIVET_DECLARE_PLUGIN(ALICE_2017_I1645239);
147
148}
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