Rivet analyses

title: BELLE_2003_I620180

Mass and helicity angles in $B^+\to\rho^+\rho^0$

Experiment: BELLE (KEKB)

Inspire ID: 620180

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.Lett. 91 (2003) 221801

Beams: * *

Beam energies: ANY

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

Mass and helicity angles in $B^+\to\rho^+\rho^0$. The background subtracted data were read from figures 2 and 3 in the paper. Due to the large asymmetry due to the cuts the $\rho^+$ helicity angle is not included.

Source code:BELLE_2003_I620180.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief B+ -> rho0 rho+ class BELLE_2003_I620180 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2003_I620180);


/// @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(113);
  BP.addStable(213);
  BP.addStable(-213);
  declare(BP, "BP");
  // histos
  book(_p[0], 1, 1, 1);
  book(_p[1], "TMP/nW");
  for (unsigned int ix = 0; ix < 2; ++ix) {
    book(_h_mass[ix], 2, 1, 1 + ix);
  }
  book(_h_angle, 3, 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 = BP.decaying()[ix].pid() / BP.decaying()[ix].abspid();
    if ((sign == 1 && BP.modeMatches(ix, 2, mode)) || (sign == -1 && BP.modeMatches(ix, 2, modeCC))) {
      const Particle& rhop = BP.decayProducts()[ix].at(sign * 213)[0];
      const Particle& rho0 = BP.decayProducts()[ix].at(113)[0];
      _h_mass[0]->fill(rho0.mass());
      _h_mass[1]->fill(rhop.mass());
      // compute the helicity angle
      if (rho0.children().size() != 2) continue;
      if (rho0.children()[0].pid() != -rho0.children()[1].pid()) continue;
      if (rho0.children()[0].abspid() != 211) continue;
      LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(
          BP.decaying()[ix].mom().betaVec());
      FourMomentum prho = boost1.transform(rho0.mom());
      FourMomentum ppi = boost1.transform(rho0.children()[0].mom());
      LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(prho.betaVec());
      ppi = boost2.transform(ppi);
      const double cTheta = ppi.p3().unit().dot(prho.p3().unit());
      _h_angle->fill(cTheta);
      _p[0]->fill(-50. * (1. - 5. * sqr(cTheta)));
      _p[1]->fill();
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  normalize(_h_mass, 1.0, false);
  normalize(_h_angle, 1.0, false);
  scale(_p[0], 1. / *_p[1]);
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h_mass[2], _h_angle;
CounterPtr _p[2];
const map<PdgId, unsigned int> mode = {{213, 1}, {113, 1}};
const map<PdgId, unsigned int> modeCC = {{-213, 1}, {113, 1}};
/// @}

};

RIVET_DECLARE_PLUGIN(BELLE_2003_I620180);

} ```