Rivet analyses

title: CRYSTAL_BALL_1989_I263581

Electron spectrum in B decays

Experiment: CRYSTAL_BALL (DORIS)

Inspire ID: 263581

Status: VALIDATED

Authors: - Peter Richardson

References: - Z.Phys.C 42 (1989) 33

Beams: * *

Beam energies: ANY

Run details: - bottom mesons produced at the Upsilon(4S)

Measurement of the inclusive electron spectrum in $B$ decays. N.B. The spectum is obtained in the rest frame of the decaying $\Upsilon(4S)$ which produces the decaying $B$ mesons

Source code:CRYSTAL_BALL_1989_I263581.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief Electron spectrum in B decays class CRYSTAL_BALL_1989_I263581 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(CRYSTAL_BALL_1989_I263581);


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

/// Book histograms and initialise projections before the run
void init() {
  // projections
  declare(UnstableParticles(), "UFS");
  // Book histograms
  // specify custom binning
  book(_h_all, 1, 1, 1);
  book(_nB, "/TMP/nB");
}

void findDecayProducts(Particle parent, Particles& em) {
  for (const Particle& p : parent.children()) {
    if (p.abspid() == PID::EMINUS) {
      em.push_back(p);
    }
    else {
      findDecayProducts(p, em);
    }
  }
}

/// Perform the per-event analysis
void analyze(const Event& event) {
  if (_edges.empty()) _edges = _h_all->xEdges();
  // find and loop over Upslion(4S)
  const UnstableParticles& ufs = apply<UnstableParticles>(event, "UFS");
  for (const Particle& p : ufs.particles(Cuts::pid == 300553)) {
    // boost to rest frame
    LorentzTransform cms_boost;
    if (p.p3().mod() > 1 * MeV) {
      cms_boost = LorentzTransform::mkFrameTransformFromBeta(p.momentum().betaVec());
    }
    // loop over decay products
    for (const Particle& p2 : p.children()) {
      if (p2.abspid() == 511 || p2.abspid() == 521) {
        _nB->fill();
        Particles em;
        findDecayProducts(p2, em);
        for (const Particle& electron : em) {
          const double en = cms_boost.transform(electron.momentum()).E();
          _h_all->fill(map2string(en));
        }
      }
    }
  }
}

string map2string(const double val) const {
  const size_t idx = _axis.index(val);
  if (idx && idx <= _edges.size()) return _edges[idx - 1];
  return "OTHER";
}


/// Normalise histograms etc., after the run
void finalize() {
  // normalize to number of B decays
  scale(_h_all, 1. / 0.05 / *_nB);
}

/// @}


/// @name Histograms
/// @{
BinnedHistoPtr<string> _h_all;
CounterPtr _nB;
YODA::Axis<double> _axis = YODA::Axis<double>(48, 0.6, 3.0);
vector<string> _edges;
/// @}

};

RIVET_DECLARE_PLUGIN(CRYSTAL_BALL_1989_I263581);

} ```