Rivet analyses

Λ_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: - DOI: 10.1007/JHEP04(2018)108 - arXiv: 1712.09581

Beam energies: ANY

Run details: none listed

The p_T-differential production cross section of prompt Λ_c⁺ charmed baryons was measured with the ALICE detector at the Large Hadron Collider (LHC) in pp collisions at $ =7 $ TeV and in p-Pb collisions at $ =5.02 $ TeV at midrapidity. The Λ_c⁺ and $ {}_{} $ were reconstructed in the hadronic decay modes Λ_c⁺→ pK⁻π⁺, Λ_c⁺→ pK_S⁰ and in the semileptonic channel Λ_c⁺→ e⁺ν_eΛ (and charge conjugates). The measured values of the Λ_c⁺ /D⁰ 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 Λ_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 Λ_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`

// -*- 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
    RIVET_DEFAULT_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 (isCompatibleWithSqrtS(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;
    Estimate1DPtr _h_LcD0, _h_LcD0Pb, _h_LcD0int, _h_LcD0Pbint, _h_RpPb;
    /// @}

  };


  RIVET_DECLARE_PLUGIN(ALICE_2017_I1645239);

}

Rivet analyses

Λc+ production in pp collisions at $\sqrt{s} = 7$ TeV and in p-Pb collisions at $\sqrt{s_\mathrm{NN}} = 5.02$ TeV

Source code:ALICE_2017_I1645239.cc

Λ_c⁺ production in pp collisions at $\sqrt{s} = 7$ TeV and in p-Pb collisions at $\sqrt{s_\mathrm{NN}} = 5.02$ TeV

Source code:`ALICE_2017_I1645239.cc`