Rivet analyses

title: BABAR_2009_I813140

$\pi^+\pi^-$ mass distriubution in $B^+\to\pi^+\pi^+\pi^-$

Experiment: BABAR (PEP-II)

Inspire ID: 813140

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 79 (2009) 072006

Beams: * *

Beam energies: ANY

Run details: - Any process producing B+ mesons originally Upsilon(4S) decay

Measurement of the $\pi^+\pi^-$ mass distriubutions in $B^+\to\pi^+\pi^+\pi^-$. The data were read from the plotsi in the paper and may not be corrected for efficiency/acceptable, although the backgrounds given in the paper have been subtracted.

Source code:BABAR_2009_I813140.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief B+ -> pi+ pi+ pi- class BABAR_2009_I813140 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2009_I813140);


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

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  UnstableParticles ufs = UnstableParticles(Cuts::abspid == 521);
  declare(ufs, "UFS");
  DecayedParticles BP(ufs);
  declare(BP, "BP");
  // histograms
  book(_h_all, 1, 1, 1);
  for (unsigned int ix = 0; ix < 3; ++ix)
    for (unsigned int iy = 0; iy < 2; ++iy) book(_h_charge[ix][iy], 2, 1 + ix, 1 + iy);
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  static const map<PdgId, unsigned int>& mode = {{-211, 1}, {211, 2}};
  static const map<PdgId, unsigned int>& modeCC = {{211, 1}, {-211, 2}};
  DecayedParticles BP = apply<DecayedParticles>(event, "BP");
  // loop over particles
  for (unsigned int ix = 0; ix < BP.decaying().size(); ++ix) {
    int sign = 1;
    if (BP.modeMatches(ix, 3, mode))
      sign = 1;
    else if (BP.modeMatches(ix, 3, modeCC))
      sign = -1;
    else
      continue;
    // particles
    const Particle& pim = BP.decayProducts()[ix].at(-sign * 211)[0];
    const Particles& pip = BP.decayProducts()[ix].at(sign * 211);
    // boost to B rest frame
    LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(
        BP.decaying()[ix].momentum().betaVec());
    FourMomentum pPim = boost.transform(pim.momentum());
    FourMomentum pPip[2];
    for (unsigned int ix = 0; ix < 2; ++ix) pPip[ix] = boost.transform(pip[ix].momentum());
    // loop over pi+
    for (unsigned int ix = 0; ix < 2; ++ix) {
      FourMomentum ppipi = pip[ix].momentum() + pim.momentum();
      double mpipi = ppipi.mass();
      _h_all->fill(mpipi);
      _h_charge[0][(1 - sign) / 2]->fill(mpipi);
      unsigned int ibatch = ix == 0 ? 1 : 0;
      Vector3 axis = pPip[ibatch].p3().unit();
      LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(ppipi.betaVec());
      Vector3 axis2 = boost1.transform(pPim).p3().unit();
      double cTheta = axis.dot(axis2);
      if (cTheta > 0) {
        _h_charge[1][(1 - sign) / 2]->fill(mpipi);
      }
      else {
        _h_charge[2][(1 - sign) / 2]->fill(mpipi);
      }
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  normalize(_h_all, 1., false);
  for (unsigned int ix = 0; ix < 3; ++ix)
    for (unsigned int iy = 0; iy < 2; ++iy) normalize(_h_charge[ix][iy], 1., false);
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h_all, _h_charge[3][2];
/// @}

};

RIVET_DECLARE_PLUGIN(BABAR_2009_I813140);

} ```