Rivet analyses

title: BELLE_2006_I688850

Helicity angle and mass distribution for $\pi^+\pi^-$ in $B^0\to\rho^0\pi^0$

Experiment: BELLE (KEKB)

Inspire ID: 688850

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 73 (2006) 111105

Beams: * *

Beam energies: ANY

Run details: - Any process producing B0 mesons, originally Upsilon(4S) decays

Measurement of the helicity angle and mass distribution for $\pi^+\pi^-$ in $B^0\to\rho^0\pi^0$

Source code:BELLE_2006_I688850.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief B0 -> rho0 pi0 class BELLE_2006_I688850 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2006_I688850);


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

/// Book histograms and initialise projections before the run
void init() {
  // projections
  UnstableParticles ufs = UnstableParticles(Cuts::abspid == 511);
  declare(ufs, "UFS");
  DecayedParticles B0(ufs);
  B0.addStable(111);
  declare(B0, "B0");
  // histos
  for (unsigned int ix = 0; ix < 2; ++ix) {
    book(_h[ix], 1, 1, 1 + ix);
  }
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  DecayedParticles B0 = apply<DecayedParticles>(event, "B0");
  for (unsigned int ix = 0; ix < B0.decaying().size(); ++ix) {
    int sign = B0.decaying()[ix].pid() / B0.decaying()[ix].abspid();
    if (!B0.modeMatches(ix, 3, mode)) continue;
    const Particle& pip = B0.decayProducts()[ix].at(sign * 211)[0];
    const Particle& pim = B0.decayProducts()[ix].at(-sign * 211)[0];
    const Particle& pi0 = B0.decayProducts()[ix].at(111)[0];
    // require pi+- pi0 mass >1.1 GeV
    if ((pip.mom() + pi0.mom()).mass() < 1.1) continue;
    if ((pim.mom() + pi0.mom()).mass() < 1.1) continue;
    FourMomentum pRho = pip.mom() + pim.mom();
    _h[0]->fill(pRho.mass());
    // compute the helicity angle
    LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(
        B0.decaying()[ix].mom().betaVec());
    pRho = boost1.transform(pRho);
    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[1]->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}, {-211, 1}, {111, 1}};
/// @}

};

RIVET_DECLARE_PLUGIN(BELLE_2006_I688850);

} ```