Rivet analyses

μ⁺μ⁻ and τ⁺τ⁻ production in two photon collisions at LEP

Experiment: L3 (LEP)

Inspire ID: 645127

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Lett. B585 (2004) 53-62, 2004

Beams: e- e+, 22 22

Beam energies: (80.5, 80.5); (86.0, 86.0); (91.5, 91.5); (94.5, 94.5); (98.0, 98.0); (103.0, 103.0); (1.8, 1.8); (2.2, 2.2); (2.8, 2.8); (3.2, 3.2); (3.8, 3.8); (4.5, 4.5); (6.2, 6.2); (8.8, 8.8); (15.0, 15.0)GeV

Run details: - e+e- -> gamma gamma producing muons and tau leptons

Measurement of e⁺e⁻ → e⁺e⁻γγ → e⁺e⁻ → e⁺e⁻μ⁺μ⁻, τ⁺τ⁻. This analysis can test approximations used to simulate this process, but also is a prototype for analyses of γγ collisions. There are two modes supported, the first PROCESS=EE, simulates for full process starting with e⁺e⁻ beams, while the second PROCESS=GG is the extracted cross section for γγ → μ⁺μ⁻.

Source code:`L3_2004_I645127.cc`

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

namespace Rivet {


  /// @brief mu+mu- and tau+tau- in gamma gamma
  class L3_2004_I645127 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(L3_2004_I645127);


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

    /// Book histograms and initialise projections before the run
    void init() {

      // get the mode and options
      _mode =0;
      if( getOption("PROCESS") == "EE" ) _mode = 0;
      else if( getOption("PROCESS") == "GG") _mode = 1;

      // Initialise and register projections
      if(_mode==0) {
    declare(GammaGammaKinematics(), "Kinematics");
        declare(GammaGammaFinalState(), "FS");
        declare(UnstableParticles(),"UFS");
        // Book histos
        book(_c_sigma_mu1, 1,1,1);
        book(_c_sigma_mu2, 1,1,2);
        book(_c_sigma_tau, 2,1,1);
      }
      else if(_mode==1) {
        declare(FinalState(), "FS");
        book(_sigma,"TMP/sigma",refData(3,1,1));
      }

    }

    void findChildren(const Particle & p,map<long,int> & nRes, int &ncount) {
      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) {
      // stuff for e+e- collisions
      double W2 = sqr(sqrtS());
      if(_mode==0) {
    const GammaGammaKinematics& kin = apply<GammaGammaKinematics>(event, "Kinematics");
    W2 = kin.W2();
    if(W2<9.*sqr(GeV) ) vetoEvent;
      }
      const FinalState& fs = apply<FinalState>(event, "FS");
      map<long,int> nCount;
      int ntotal(0);
      bool fiducal = true;
      for(const Particle & p : fs.particles()) {
        nCount[p.pid()] += 1;
        ++ntotal;
    if(abs(p.pid())==13) {
      if(abs(cos(p.momentum().polarAngle()))>0.8) fiducal = false;
    }
      }
      if( nCount[-13]==1 && nCount[13]==1 && ntotal==2+nCount[22]) {
    if(W2<1600.*sqr(GeV) && _c_sigma_mu1) {
          _c_sigma_mu2->fill(round(sqrtS()));
          if(fiducal) _c_sigma_mu1->fill(round(sqrtS()));
        }
        if(_sigma) _sigma->fill(sqrtS());
      }
      if(_mode==1) return;
      bool foundTauPlus = false, foundTauMinus = true;
      const UnstableParticles & ufs = apply<UnstableParticles>(event, "UFS");
      for (const Particle& p : ufs.particles()) {
    if(p.children().empty()) continue;
        // find the taus
        if(abs(p.pid())==15) {
      if(p.pid()== 15) foundTauMinus=true;
      if(p.pid()==-15) foundTauPlus =true;
          findChildren(p,nCount,ntotal);
    }
      }
      if(!foundTauPlus || !foundTauMinus)
    vetoEvent;
      bool matched = true;
      for(auto const & val : nCount) {
    if(val.first==22) {
      continue;
    }
    else if(val.second!=0) {
      matched = false;
      break;
    }
      }
      if(matched)
    _c_sigma_tau->fill(round(sqrtS()));
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      // prefactor for the cross sections
      double fact  = crossSection()/picobarn/sumOfWeights();
      if(_mode==0) {
        scale(_c_sigma_mu1,fact);
        scale(_c_sigma_mu2,fact);
        scale(_c_sigma_tau,fact);
      }
      else {
        fact /= 1000.;
        scale(_sigma,fact);
        for(unsigned int iy=1;iy<6;++iy) {
          Estimate1DPtr tmp;
          book(tmp,3,1,iy);
          barchart(_sigma,tmp);
        }
      }
    }

    /// @}


    /// @name Histograms
    /// @{
    BinnedHistoPtr<int> _c_sigma_mu1,_c_sigma_mu2,_c_sigma_tau;
    Histo1DPtr _sigma;
    unsigned int _mode;
    /// @}


  };


  RIVET_DECLARE_PLUGIN(L3_2004_I645127);


}

Rivet analyses

μ+μ− and τ+τ− production in two photon collisions at LEP

Source code:L3_2004_I645127.cc

μ⁺μ⁻ and τ⁺τ⁻ production in two photon collisions at LEP

Source code:`L3_2004_I645127.cc`