Rivet analyses

Cross sections for e⁺e⁻ → J/ψ + π⁺π⁻, π⁰π⁰ or K⁺K⁻

Experiment: CLEO (CESR)

Inspire ID: 710864

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.Lett. 96 (2006) 162003

Beams: * *

Beam energies: (2.0, 2.0); (2.1, 2.1); (2.1, 2.1)GeV

Run details: - For the cross sections e+e- -> hadrons at 4.015, 4.160 or 4.260 GeV, any process producing psi(4230) for decays. pi0 should be set stable

Measurement of the cross section for e⁺e⁻ → J/ψ + π⁺π⁻, π⁰π⁰ or K⁺K⁻ at $\sqrt{s}=4.015$, 4.160 or 4.260 GeV to study the properties of ψ(4040) , ψ(4160) and Y(4260) (now ψ(4230)). Two modes are provided, one for the e⁺e⁻ cross secions (MODE=SIGMA) and a second which implements the measured mass distribution in Y(4260) → J/ψπ⁺π⁻ decays. There is no consensus as to the nature of the ψ(4230) cc̄ state and therefore we taken its PDG code to be 9030443, i.e. the first unused code for an undetermined spin one cc̄ state. This can be changed using the PID option if a different code is used by the event generator performing the simulation.

Source code:`CLEO_2006_I710864.cc`

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

namespace Rivet {


  /// @brief Cross sections for $e^+e^-\to J/\psi + \pi^+\pi^-$, $\pi^0\pi^0$ or $K^+K^-$
  class CLEO_2006_I710864 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(CLEO_2006_I710864);


    /// @name Analysis methods
    /// @{

    /// Book histograms and initialise projections before the run
    void init() {
      // set the PDG code
      _pid = getOption<int>("PID", 9030443);
      // setup for cross sections
      declare(FinalState(), "FS");
      declare(UnstableParticles(Cuts::pid== 443), "UFS");
      // histograms
      for (unsigned int ix=0; ix<3; ++ix) {
        book(_sigma[ix],1,1,1+ix);
      }
      for (const string& en : _sigma[0].binning().edges<0>()) {
        const size_t idx = en.find("to");
        if (idx != string::npos) {
          const double emin = std::stod(en.substr(0,idx));
          const double emax = std::stod(en.substr(idx+2,string::npos));
          if (inRange(sqrtS()/GeV, emin, emax)) {
            _sqs = en;
            break;
          }
        }
        else {
          const double eval = stod(en);
          if (isCompatibleWithSqrtS(eval)) {
            _sqs = en; break;
          }
        }
      }
      raiseBeamErrorIf(_sqs.empty());

      // projections for decays
      DecayedParticles PSI(UnstableParticles(Cuts::abspid==_pid));
      PSI.addStable(443);
      declare(PSI, "PSI");
      book(_h,2,1,1);
    }

    void findChildren(const Particle& p, map<long,int>& nRes, int& ncount) const {
      for (const Particle& child : p.children()) {
        if (child.children().empty()) {
          --nRes[child.pid()];
          --ncount;
        }
        else {
          findChildren(child,nRes,ncount);
        }
      }
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      // cross section
      const FinalState& fs = apply<FinalState>(event, "FS");
      map<long,int> nCount;
      int ntotal(0);
      for (const Particle& p : fs.particles()) {
        nCount[p.pid()] += 1;
        ++ntotal;
      }
      for (const Particle& psi : apply<UnstableParticles>(event, "UFS").particles()) {
        if (psi.children().empty()) continue;
        map<long,int> nRes = nCount;
        int ncount = ntotal;
        findChildren(psi,nRes,ncount);
        if (ncount!=2) continue;
        if (nRes.find(211)!=nRes.end() && nRes.find(-211)!=nRes.end() &&
            nRes[211]==1 && nRes[-211]==1) {
          _sigma[0]->fill(_sqs);
          break;
        }
        else if (nRes.find(111)!=nRes.end() && nRes[111]==2) {
          _sigma[1]->fill(_sqs);
          break;
        }
        else if (nRes.find(321)!=nRes.end() && nRes.find(-321)!=nRes.end() &&
                 nRes[321]==1 && nRes[-321]==1) {
          _sigma[2]->fill(_sqs);
          break;
        }
      }
      // decays
      DecayedParticles PSI = apply<DecayedParticles>(event, "PSI");
      for (unsigned int ix=0; ix<PSI.decaying().size(); ++ix) {
        if (!PSI.modeMatches(ix,3,mode)) continue;
        const Particle & pip  = PSI.decayProducts()[ix].at( 211)[0];
        const Particle & pim  = PSI.decayProducts()[ix].at(-211)[0];
        double mpipi = (pip.mom()+pim.mom()).mass();
        _h->fill(mpipi);
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      // sigma
      scale(_sigma, crossSection()/ sumOfWeights() /picobarn);
      // decay
      normalize(_h, 1.0, false);
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h;
    BinnedHistoPtr<string> _sigma[3];
    string _sqs = "";
    int _pid;
    const map<PdgId,unsigned int> mode = { { 211,1}, {-211,1}, { 443,1}};
    /// @}


  };


  RIVET_DECLARE_PLUGIN(CLEO_2006_I710864);

}

Rivet analyses

Cross sections for e+e− → J/ψ + π+π−, π0π0 or K+K−

Source code:CLEO_2006_I710864.cc

Cross sections for e⁺e⁻ → J/ψ + π⁺π⁻, π⁰π⁰ or K⁺K⁻

Source code:`CLEO_2006_I710864.cc`