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 (const auto& 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`