Rivet analyses

title: BELLE_2015_I1330289

Measurement of the spectrum for $\bar{B}\to X_s \gamma$

Experiment: BELLE (KEKB)

Inspire ID: 1330289

Status: VALIDATED

Authors: - Peter Richardson

References: - PR D91,052004

Beams: * *

Beam energies: ANY

Run details: - any process making $B^-$ and $\bar{B}^0$ mesons, eg. particle gun or $\Upslion(4S)$ decay.

Mass spectrum in $B\to s\gamma$ decays measured by BELLE. Useful for testing the implementation of these decays

Source code:BELLE_2015_I1330289.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief B -> X_s gamma spectrum class BELLE_2015_I1330289 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2015_I1330289);


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

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

  // Initialise and register projections
  declare(UnstableParticles(), "UFS");

  // Book histograms
  book(_h_spectrum, 1, 1, 2);
  book(_nBottom, "TMP/BottomCounter");
}


void findDecayProducts(const Particle& mother,
                       unsigned int& nK0,
                       unsigned int& nKp,
                       unsigned int& nKm,
                       FourMomentum& ptot) {
  for (const Particle& p : mother.children()) {
    int id = p.pid();
    if (id == PID::KPLUS) {
      ++nKp;
      ptot += p.momentum();
    }
    else if (id == PID::KMINUS) {
      ++nKm;
      ptot += p.momentum();
    }
    else if (id == PID::K0S) {
      ++nK0;
      ptot += p.momentum();
    }
    else if (id == PID::PI0 || id == PID::PIPLUS || id == PID::PIMINUS) {
      ptot += p.momentum();
    }
    else if (!p.children().empty()) {
      findDecayProducts(p, nK0, nKp, nKm, ptot);
    }
    else
      ptot += p.momentum();
  }
}


/// Perform the per-event analysis
void analyze(const Event& event) {

  // Loop over bottoms
  for (const Particle& bottom : apply<UnstableParticles>(event, "UFS").particles()) {
    if (bottom.pid() != -521 && bottom.pid() != -511) continue;
    FourMomentum pgamma(0., 0., 0., 0.);
    unsigned int ngamma = 0;
    bool fs = true;
    for (const Particle& child : bottom.children()) {
      if (child.pid() == bottom.pid()) {
        fs = false;
        break;
      }
      else if (child.pid() == PID::PHOTON) {
        ngamma += 1;
        pgamma += child.momentum();
      }
    }
    if (!fs) continue;
    _nBottom->fill();
    if (ngamma != 1) continue;
    unsigned int nK0(0), nKp(0), nKm(0);
    FourMomentum p_tot(0, 0, 0, 0);
    findDecayProducts(bottom, nK0, nKp, nKm, p_tot);
    unsigned int nk = nKp - nKm + nK0;
    if (nk % 2 == 1) {
      p_tot -= pgamma;
      _h_spectrum->fill(p_tot.mass() / GeV);
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  scale(_h_spectrum, 1e6 / _nBottom->sumW());
  // multiply by the bin width
  for (size_t ix = 0; ix < _h_spectrum->numBins(); ++ix) {
    _h_spectrum->bin(ix + 1).scaleW(_h_spectrum->bin(ix + 1).xWidth());
  }
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h_spectrum;
CounterPtr _nBottom;
/// @}

};

RIVET_DECLARE_PLUGIN(BELLE_2015_I1330289);

} ```