Rivet analyses

title: BELLE_2006_I689881

Measurement of the kaon helicity angle in $B^0\to \chi_{c1} K^{*0}$

Experiment: BELLE (KEKB)

Inspire ID: 689881

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Lett.B 634 (2006) 155-164

Beams: * *

Beam energies: ANY

Run details: - Any process producing B mesons, orginally Upsilon(4S) decay

Measurement of the $K^$ helicity angle in the charmonium decay for $B^0\to \chi_{c1} K^{0}$. The data were read from Figure 5 in the paper which is corrected for efficiency/acceptance.

Source code:BELLE_2006_I689881.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief B -> chi_c1 K* class BELLE_2006_I689881 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2006_I689881);


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

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  UnstableParticles ufs = UnstableParticles(Cuts::abspid == 511);
  declare(ufs, "UFS");
  // histograms
  book(_h, 1, 1, 1);
}

bool isK(int pid) const {
  return pid == 130 || pid == 310 || pid == 311 || pid == 321;
}

bool isPi(int pid) const {
  return pid == 211 || pid == 111;
}

/// Perform the per-event analysis
void analyze(const Event& event) {
  UnstableParticles ufs = apply<UnstableParticles>(event, "UFS");
  for (const Particle& B : ufs.particles()) {
    if (B.children().size() != 2) continue;
    Particle chic, Kstar;
    if (B.children()[0].pid() == 20443 && B.children()[1].abspid() == 313) {
      chic = B.children()[0];
      Kstar = B.children()[1];
    }
    else if (B.children()[1].pid() == 20443 && B.children()[0].abspid() == 313) {
      chic = B.children()[1];
      Kstar = B.children()[0];
    }
    else {
      continue;
    }
    // find Kstar decay products
    Particle K;
    if (isK(Kstar.children()[0].abspid()) && isPi(Kstar.children()[1].abspid())) {
      K = Kstar.children()[0];
    }
    else if (isK(Kstar.children()[1].abspid()) && isPi(Kstar.children()[0].abspid())) {
      K = Kstar.children()[1];
    }
    else {
      continue;
    }
    // boost to B rest frame
    LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(B.momentum().betaVec());
    FourMomentum pChi = boost.transform(chic.momentum());
    FourMomentum pKstar = boost.transform(Kstar.momentum());
    FourMomentum pK = boost.transform(K.momentum());
    // axes
    Vector3 axisX = pChi.p3().unit();
    // kaon helicity angle
    LorentzTransform boostK = LorentzTransform::mkFrameTransformFromBeta(pKstar.betaVec());
    double cosK = -axisX.dot(boostK.transform(pK).p3().unit());
    // fill hists
    _h->fill(cosK);
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  normalize(_h, 1., false);
}

/// @}


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

};

RIVET_DECLARE_PLUGIN(BELLE_2006_I689881);

} ```