Rivet analyses

title: BELLE_2005_I651511

Helicity angle and $\pi^+\pi^0$ mass in $B^+\to\pi^+\pi^0\pi^0$

Experiment: BELLE (KEKB)

Inspire ID: 651511

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.Lett. 94 (2005) 031801

Beams: * *

Beam energies: ANY

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

Measurement of the Helicity angle and $\pi^+\pi^0$ mass in $B^+\to\pi^+\pi^0\pi^0$. The background subracted was read from figures 2 and 3 in the paper.

Source code:BELLE_2005_I651511.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief B+ -> pi+ pi0 pi0 class BELLE_2005_I651511 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2005_I651511);


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

/// Book histograms and initialise projections before the run
void init() {
  // projections
  UnstableParticles ufs = UnstableParticles(Cuts::abspid == 521);
  declare(ufs, "UFS");
  DecayedParticles BP(ufs);
  BP.addStable(111);
  declare(BP, "BP");
  // histos
  for (unsigned int ix = 0; ix < 2; ++ix) {
    book(_h[ix], 1 + ix, 1, 1);
  }
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  DecayedParticles BP = apply<DecayedParticles>(event, "BP");
  for (unsigned int ix = 0; ix < BP.decaying().size(); ++ix) {
    int sign = 1;
    if (BP.decaying()[ix].pid() > 0 && BP.modeMatches(ix, 3, mode))
      sign = 1;
    else if (BP.decaying()[ix].pid() < 0 && BP.modeMatches(ix, 3, modeCC))
      sign = -1;
    else
      continue;
    const Particle& pip = BP.decayProducts()[ix].at(sign * 211)[0];
    const Particles& pi0 = BP.decayProducts()[ix].at(111);
    FourMomentum pRho[2] = {pip.mom() + pi0[0].mom(), pip.mom() + pi0[1].mom()};
    double mRho[2] = {pRho[0].mass(), pRho[1].mass()};
    unsigned int iloc = mRho[0] < mRho[1] ? 0 : 1;
    _h[1]->fill(mRho[iloc]);
    // compute the helicity angles
    LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(
        BP.decaying()[ix].mom().betaVec());
    FourMomentum prho = boost1.transform(pRho[iloc]);
    FourMomentum ppi = boost1.transform(pip.mom());
    LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(prho.betaVec());
    ppi = boost2.transform(ppi);
    const double cTheta = ppi.p3().unit().dot(prho.p3().unit());
    _h[0]->fill(cTheta);
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  normalize(_h, 1.0, false);
}
/// @}


/// @name Histograms
/// @{
Histo1DPtr _h[2];
const map<PdgId, unsigned int> mode = {{211, 1}, {111, 2}};
const map<PdgId, unsigned int> modeCC = {{-211, 1}, {111, 2}};
/// @}

};

RIVET_DECLARE_PLUGIN(BELLE_2005_I651511);

} ```