Rivet analyses

title: DELPHI_1995_I395026

Production of $B^*$ mesons at LEP1

Experiment: DELPHI (LEP)

Inspire ID: 395026

Status: VALIDATED

Authors: - Peter Richardson

References: - Z.Phys. C68 (1995) 353-362

Beams: e- e+

Beam energies: (45.6, 45.6)GeV

Run details: - e+e- to hadrons

Spectrum for the production of $B^*$ mesons at LEP1. The polarization and ratio of vector to pseudoscalar $B$ meson production is also measured.

Source code:DELPHI_1995_I395026.cc

```c++ // -- C++ --

include "Rivet/Analysis.hh"

include "Rivet/Projections/Beam.hh"

include "Rivet/Projections/ChargedFinalState.hh"

include "Rivet/Projections/UnstableParticles.hh"

define I_KNOW_THE_INITIAL_QUARKS_PROJECTION_IS_DODGY_BUT_NEED_TO_USE_IT

include "Rivet/Projections/InitialQuarks.hh"

namespace Rivet {

/// @brief B* production at LEP1 class DELPHI_1995_I395026 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(DELPHI_1995_I395026);


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

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

  // // Initialise and register projections
  declare(Beam(), "Beams");
  declare(ChargedFinalState(), "FS");
  declare(InitialQuarks(), "IQF");
  declare(UnstableParticles(), "UFS");

  // Book histograms
  book(_h_ctheta1, 5, 1, 1);
  book(_h_ctheta2, "/TMP/ctheta", 20, -1., 1.);
  book(_h_z, 4, 1, 1);
  book(_c_hadron, "/TMP/chadron");
  book(_c_bottom, "/TMP/cbottom");
  book(_c_bStar, "/TMP/cbStar ");
  book(_c_B, "/TMP/cB     ");
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  // First, veto on leptonic events by requiring at least 4 charged FS particles
  const FinalState& fs = apply<FinalState>(event, "FS");
  const size_t numParticles = fs.particles().size();

  // Even if we only generate hadronic events, we still need a cut on numCharged >= 2.
  if (numParticles < 2) {
    MSG_DEBUG("Failed leptonic event cut");
    vetoEvent;
  }
  MSG_DEBUG("Passed leptonic event cut");

  int flavour = 0;
  const InitialQuarks& iqf = apply<InitialQuarks>(event, "IQF");

  // If we only have two quarks (qqbar), just take the flavour.
  // If we have more than two quarks, look for the highest energetic q-qbar pair.
  if (iqf.particles().size() == 2) {
    flavour = iqf.particles().front().abspid();
  }
  else {
    map<int, double> quarkmap;
    for (const Particle& p : iqf.particles()) {
      if (quarkmap[p.pid()] < p.E()) {
        quarkmap[p.pid()] = p.E();
      }
    }
    double maxenergy = 0.;
    for (int i = 1; i <= 5; ++i) {
      if (quarkmap[i] + quarkmap[-i] > maxenergy) {
        flavour = i;
      }
    }
  }
  if (flavour == 5) _c_bottom->fill();
  _c_hadron->fill();
  // Get beams and average beam momentum
  const ParticlePair& beams = apply<Beam>(event, "Beams").beams();
  const double meanBeamMom = (beams.first.p3().mod() + beams.second.p3().mod()) / 2.0;
  MSG_DEBUG("Avg beam momentum = " << meanBeamMom);

  // loop over the particles
  for (const Particle& p : apply<UnstableParticles>(event, "UFS")
                               .particles(Cuts::abspid == 513 or Cuts::abspid == 523
                                          or Cuts::abspid == 511 or Cuts::abspid == 521)) {
    int sign = p.pid() / p.abspid();
    // count number of Bs not from mixing or B*
    if (p.abspid() == 511 || p.abspid() == 521) {
      if (p.parents()[0].abspid() == p.abspid()) continue;
      if (p.parents()[0].abspid() == 513 || p.parents()[0].abspid() == 523) continue;
      _c_B->fill();
    }
    // B*
    else {
      _c_bStar->fill();
      double xE = p.momentum().t() / meanBeamMom;
      _h_z->fill(xE);
      Particle decay;
      if (p.children().size() != 2) continue;
      int mid = p.abspid() - 2;
      if (p.children()[0].pid() == sign * mid && p.children()[1].pid() == 22) {
        decay = p.children()[1];
      }
      else if (p.children()[1].pid() == sign * mid && p.children()[0].pid() == 22) {
        decay = p.children()[0];
      }
      else
        continue;
      LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(p.momentum().betaVec());
      Vector3 e1z = p.p3().unit();
      FourMomentum pp = boost.transform(decay.momentum());
      Vector3 axis1 = boost.transform(decay.momentum()).p3().unit();
      double ctheta = e1z.dot(axis1);
      _h_ctheta1->fill(ctheta);
      _h_ctheta2->fill(ctheta);
    }
  }
}

pair<double, double> calcRho(Histo1DPtr hist) {
  if (hist->numEntries() == 0.) return make_pair(0., 0.);
  double sum1(0.), sum2(0.);
  for (const auto& bin : hist->bins()) {
    double Oi = bin.sumW();
    if (Oi == 0.) continue;
    double ai = 0.125 * (-bin.xMin() * (3. + sqr(bin.xMin())) + bin.xMax() * (3. + sqr(bin.xMax())));
    double bi = 0.375 * (-bin.xMin() * (1. - sqr(bin.xMin())) + bin.xMax() * (1. - sqr(bin.xMax())));
    double Ei = bin.errW();
    sum1 += sqr(bi / Ei);
    sum2 += bi / sqr(Ei) * (Oi - ai);
  }
  return make_pair(sum2 / sum1, sqrt(1. / sum1));
}

/// Normalise histograms etc., after the run
void finalize() {
  // spectrum
  scale(_h_z, 1. / _c_hadron->val());
  // polarization
  scale(_h_ctheta1, 1. / _c_hadron->val());
  normalize(_h_ctheta2);
  pair<double, double> rho = calcRho(_h_ctheta2);
  BinnedEstimatePtr<string> h_rho;
  book(h_rho, 3, 1, 1);
  h_rho->bin(1).set(rho.first, rho.second);
  // no of B* per hadronic Z
  double val = _c_bStar->val() / _c_hadron->val();
  double err = val
      * sqrt(sqr(_c_bStar->err() / _c_bStar->val()) + sqr(_c_hadron->err() / _c_hadron->val()));
  BinnedEstimatePtr<string> h_nBS;
  book(h_nBS, 2, 1, 1);
  h_nBS->bin(1).set(val, err);
  // no of B* per b bbar
  val = _c_bStar->val() / _c_bottom->val();
  err = val * sqrt(sqr(_c_bStar->err() / _c_bStar->val()) + sqr(_c_bottom->err() / _c_bottom->val()));
  BinnedEstimatePtr<string> h1;
  book(h1, 1, 1, 1);
  h1->bin(1).set(val, err);
  Counter ctemp = *_c_bStar + *_c_B;
  // no of B*/B+B*
  val = _c_bStar->val() / ctemp.val();
  err = val * sqrt(sqr(_c_bStar->err() / _c_bStar->val()) + sqr(ctemp.err() / ctemp.val()));
  h1->bin(2).set(val, err);
  // average x_E
  val = _h_z->xMean();
  err = _h_z->xStdErr();
  h1->bin(3).set(val, err);
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h_ctheta1, _h_ctheta2, _h_z;
CounterPtr _c_hadron, _c_bottom, _c_bStar, _c_B;
/// @}

};

RIVET_DECLARE_PLUGIN(DELPHI_1995_I395026);

} ```