Rivet analyses

title: BELLE_2022_I2167323

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

Experiment: BELLE (KEKB)

Inspire ID: 2167323

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - arXiv: 2210.10220

Beams: * *

Beam energies: ANY

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

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

Source code:BELLE_2022_I2167323.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief B -> s gamma class BELLE_2022_I2167323 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2022_I2167323);


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

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  declare(UnstableParticles(Cuts::abspid == 521 || Cuts::abspid == 511), "UFS");
  // Book histograms
  book(_h_spectrum, 1, 1, 1);
  book(_nBottom, "TMP/BottomCounter");
}

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

/// Perform the per-event analysis
void analyze(const Event& event) {
  // Loop over bottoms
  for (const Particle& bottom : apply<UnstableParticles>(event, "UFS").particles()) {
    // remove mixing entries etc
    if (bottom.children()[0].abspid() == bottom.abspid()) continue;
    _nBottom->fill();
    FourMomentum pgamma(0., 0., 0., 0.);
    unsigned int ngamma = 0;
    for (const Particle& child : bottom.children()) {
      if (child.pid() == PID::PHOTON) {
        ngamma += 1;
        pgamma += child.momentum();
      }
    }
    if (ngamma != 1) continue;
    unsigned int nK0(0), nKp(0), nKm(0);
    FourMomentum p_tot(0, 0, 0, 0);
    findDecayProducts(bottom, nK0, nKp, nKm);
    unsigned int nk = nKp - nKm + nK0;
    if (nk % 2 == 1) {
      const LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(
          bottom.momentum().betaVec());
      double eGamma = boost.transform(pgamma).E();
      _h_spectrum->fill(eGamma);
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  scale(_h_spectrum, 1e4 / _nBottom->sumW());
}

/// @}


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

};

RIVET_DECLARE_PLUGIN(BELLE_2022_I2167323);

} ```