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ALICE_2017_I1645239

$\Lambda_\mathrm{c}^+$ production in pp collisions at $\sqrt{s} = 7$ TeV and in p-Pb collisions at $\sqrt{s_\mathrm{NN}} = 5.02$ TeV
Experiment: ALICE (LHC)
Inspire ID: 1645239
Status: VALIDATED
Authors:
  • Marco Giacalone
References: Beam energies: ANY
    No run details listed

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
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// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FastJets.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {


  /// Lambda_c production in pp collisions at 7 TeV and in p-Pb collisions at sqrt{sNN} = 5.02 TeV
  class ALICE_2017_I1645239 : public Analysis {
  public:

    /// Constructor
    DEFAULT_RIVET_ANALYSIS_CTOR(ALICE_2017_I1645239);


    /// @name Analysis methods
    //@{

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      declare(UnstableParticles(Cuts::absrap < 0.96), "upProj");

      // Book histograms
      book(_h_Lc, 1, 1, 1);                                  // Lc in pp at 7 TeV
      book(_h_LcPb, 2, 1, 1);                                // Lc in p-Pb at 5.02 TeV
      book(_h_LcD0, 3, 1, 1);                                // Lc/D0 in pp at 7 TeV
      book(_h_LcD0Pb, 4, 1, 1);                              // Lc/D0 in p-Pb at 5.02 TeV
      book(_h_LcD0int, 5, 1, 1);                             // "Integrated" Lc/D0 in pp at 7 TeV (1 < pT < 8 GeV/c)
      book(_h_LcD0Pbint, 6, 1, 1);                           // "Integrated" Lc/D0 in p-Pb at 5.02 TeV (2 < pT < 12 GeV/c)
      book(_h_RpPb, 7, 1, 1);                                // RpPb
      book(_h_Lcdummy, "TMP/Lcdummy", refData(3, 1, 1));     // Lc in pp at 7 TeV with (_h_LcD0) binning
      book(_h_D0, "TMP/D0", refData(3, 1, 1));               // D0 in pp at 7 TeV with (_h_LcD0) binning
      book(_h_LcPbdummy, "TMP/LcPbdummy", refData(4, 1, 1)); // Lc in p-Pb at 5.02 TeV with (_h_LcD0Pb) binning
      book(_h_D0Pb, "TMP/D0Pb", refData(4, 1, 1));           // D0 in p-Pb at 5.02 TeV with (_h_LcD0Pb) binning
      book(_h_Lcint, "TMP/Lcint", refData(5, 1, 1));         // "Integrated" Lc in pp at 7 TeV with (_h_LcD0int) binning
      book(_h_D0int, "TMP/D0int", refData(5, 1, 1));         // "Integrated" D0 in pp at 7 TeV with (_h_LcD0int) binning
      book(_h_LcintPb, "TMP/LcintPb", refData(6, 1, 1));     // "Integrated" Lc in p-Pb at 5.02 TeV with (_h_LcD0Pbint) binning
      book(_h_D0intPb, "TMP/D0intPb", refData(6, 1, 1));     // "Integrated" D0 in p-Pb at 5.02 TeV with (_h_LcD0Pbint) binning
      book(_h_LcR, "TMP/LcR", refData(7, 1, 1));             // Lc in pp at 5.02 TeV with (_h_RpPb) binning
      book(_h_LcRPb, "TMP/LcRPb", refData(7, 1, 1));         // Lc in p-Pb at 5.02 TeV with (_h_RpPb) binning
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      PdgIdPair beamp = beamIds();
      const UnstableParticles& upProj = apply<UnstableParticles>(event, "upProj");

      // PDG code IDs used in the code: 2212 = p+, 4122 = Lc, 421 = D0, 1000822080 = Pb
      if (beamp.first == PID::PROTON && beamp.second == PID::PROTON) {
        // pp cycle
        if (fuzzyEquals(sqrtS(), 5020*GeV)) { // pp 5.02 TeV
          for (const Particle& p : upProj.particles()) {
            if (p.fromBottom()) continue;
            if (p.rap() < 0.04 && p.rap() > -0.96) {
              // NOTE : when building the Lc reference at 5.02 TeV in pp, we
              // use directly here the rapidity range covered in p-Pb In the
              // absence of real data Lc pp 5.02 TeV, the ALICE publication
              // uses an FONLL-based extrapolation from Lc pp data : i) at
              // sqrt(s) = 7 TeV ii) in |y| < 0.5, with dedicated systematic
              // uncertainties due this choice.
              if (p.abspid() == 4122) _h_LcR->fill(p.pT() / GeV);
            }
          }
        } else { // pp 7 TeV
          for (const Particle& p : upProj.particles()) {
            if (p.fromBottom()) continue;
            if (p.absrap() < 0.5) {
              if (p.abspid() == 421) {
                _h_D0->fill(p.pT() / GeV);
                _h_D0int->fill(0);
              } // end if D0
              else if (p.abspid() == 4122) {
                _h_Lc->fill(p.pT() / GeV);
                _h_Lcdummy->fill(p.pT() / GeV);
                _h_Lcint->fill(0);
              } // end if Lc
            }   // end if |y| < 0.5
          }
        }
      } // end if pp beams
      else if ((beamp.first == 2212 && beamp.second == 1000822080) || (beamp.second == 2212 && beamp.first == 1000822080)) {
        // p-Pb cycle at 5.02 TeV
        for (const Particle& p : upProj.particles()) {
          if (p.fromBottom()) continue;
          if (p.rap() < 0.04 && p.rap() > -0.96) {
            if (p.abspid() == 421) {
              _h_D0Pb->fill(p.pT() / GeV);
              _h_D0intPb->fill(-0.5);
            } // end if D0
            else if (p.abspid() == 4122) {
              _h_LcPb->fill(p.pT() / GeV);
              _h_LcPbdummy->fill(p.pT() / GeV);
              _h_LcRPb->fill(p.pT() / GeV);
              _h_LcintPb->fill(-0.5);
            } // if Lc
          } // end if -0.96 < y< 0.04
        }
      } // end p-Pb
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      // NOTE 1 : At this point cross sections consider both particles and
      // antiparticles, hence a factor 2 is added in the histos normalization
      // in order to account for this (as done in the paper) NOTE 2 : any
      // rapidity range here is 1-unit wide (in pp and p-Pb), no further
      // division by 1 is requested to get dsigma/dpTdy cross section
      if (_h_D0->numEntries() > 0) scale(_h_D0, crossSection() / (microbarn * 2 * sumOfWeights())); // norm to cross section
      if (_h_D0int->numEntries() > 0) scale(_h_D0int, crossSection() / (microbarn * 2 * sumOfWeights())); // norm to cross section
      if (_h_Lc->numEntries() > 0) scale(_h_Lc, crossSection() / (microbarn * 2 * sumOfWeights())); // norm to cross section
      if (_h_Lcdummy->numEntries() > 0) scale(_h_Lcdummy, crossSection() / (microbarn * 2 * sumOfWeights())); // norm to cross section
      if (_h_LcPbdummy->numEntries() > 0) scale(_h_LcPbdummy, crossSection() / (microbarn * 2 * sumOfWeights())); // norm to cross section
      if (_h_Lcint->numEntries() > 0) scale(_h_Lcint, crossSection() / (microbarn * 2 * sumOfWeights())); // norm to cross section
      if (_h_D0Pb->numEntries() > 0) scale(_h_D0Pb, crossSection() / (microbarn * 2 * sumOfWeights())); // norm to cross section
      if (_h_D0intPb->numEntries() > 0) scale(_h_D0intPb, crossSection() / (microbarn * 2 * sumOfWeights())); // norm to cross section
      if (_h_LcPb->numEntries() > 0) scale(_h_LcPb, crossSection() / (microbarn * 2 * sumOfWeights())); // norm to cross section
      if (_h_LcintPb->numEntries() > 0) scale(_h_LcintPb, crossSection() / (microbarn * 2 * sumOfWeights())); // norm to cross section

      if (_h_Lcdummy->numEntries() > 0 && _h_D0->numEntries() > 0) divide(_h_Lcdummy, _h_D0, _h_LcD0);
      if (_h_LcPbdummy->numEntries() > 0 && _h_D0Pb->numEntries() > 0) divide(_h_LcPbdummy, _h_D0Pb, _h_LcD0Pb);
      if (_h_Lcint->numEntries() > 0 && _h_D0int->numEntries() > 0) divide(_h_Lcint, _h_D0int, _h_LcD0int);
      if (_h_LcintPb->numEntries() > 0 && _h_D0intPb->numEntries() > 0) divide(_h_LcintPb, _h_D0intPb, _h_LcD0Pbint);

      if (_h_LcR->numEntries() > 0) scale(_h_LcR, 208 * crossSection() / (microbarn * 2 * sumOfWeights())); // norm to cross section, 208 is Z_Pb
      if (_h_LcRPb->numEntries() > 0) scale(_h_LcRPb, crossSection() / (microbarn * 2 * sumOfWeights())); // norm to cross section
      if (_h_LcRPb->numEntries() > 0 && _h_LcR->numEntries() > 0) divide(_h_LcRPb, _h_LcR, _h_RpPb);
    }

    //@}


    /// @name Histograms
    //@{
    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;
    Scatter2DPtr _h_LcD0, _h_LcD0Pb, _h_LcD0int, _h_LcD0Pbint, _h_RpPb;
    //@}

  };


  // The hook for the plugin system
  DECLARE_RIVET_PLUGIN(ALICE_2017_I1645239);

}