Rivet analyses

title: BABAR_2012_I1122031

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

Experiment: BABAR (PEP-II)

Inspire ID: 1122031

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 86 (2012) 052012

Beams: * *

Beam energies: ANY

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

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

Source code:BABAR_2012_I1122031.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief B -> Xs gamma class BABAR_2012_I1122031 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2012_I1122031);


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

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  declare(UnstableParticles(), "UFS");
  // Book histograms
  book(_h, 1, 1, 1);
  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(Cuts::abspid == 521 || Cuts::abspid == 511)) {
    // remove mixing entries etc
    for (const Particle& child : bottom.children())
      if (child.abspid() == 511 || child.pid() == bottom.pid()) 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, p_tot);
    unsigned int nk = nKp - nKm + nK0;
    if (nk % 2 == 1) {
      p_tot -= pgamma;
      _h->fill(p_tot.mass() / GeV);
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  scale(_h, 1e6 / _nBottom->sumW());
}

/// @}


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

};

RIVET_DECLARE_PLUGIN(BABAR_2012_I1122031);

} ```