Rivet analyses

title: CLEO_2001_I535113

$K^$ helicity angle in $B\to\psi(2S)K^$

Experiment: CLEO (CESR)

Inspire ID: 535113

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 63 (2001) 031103

Beams: * *

Beam energies: ANY

Run details: none listed

Measurement of the $K^$ helicity angle in the charmonium decay for $B\to K^ \psi(2S)$. The data were read from figure 2 in the paper and the backgrounds given subtracted.

Source code:CLEO_2001_I535113.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief B -> K* psi(2S) class CLEO_2001_I535113 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(CLEO_2001_I535113);


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

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  UnstableParticles ufs = UnstableParticles(Cuts::abspid == 511 || Cuts::abspid == 521);
  declare(ufs, "UFS");
  // histos
  for (unsigned int ix = 0; ix < 3; ++ix) {
    book(_h[ix], 1, 1, 1 + ix);
  }
}

bool isKstar(int pid) const {
  return pid == 313 || pid == 323;
}

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 onium, Kstar;
    if (B.children()[0].pid() == 100443 && isKstar(B.children()[1].abspid())) {
      onium = B.children()[0];
      Kstar = B.children()[1];
    }
    else if (B.children()[1].pid() == 100443 && isKstar(B.children()[0].abspid())) {
      onium = 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;
    }
    unsigned int imode = 0;
    if (B.abspid() == 511 && K.abspid() == 321)
      imode = 2;
    else if (B.abspid() == 521) {
      if (K.abspid() == 321)
        imode = 1;
      else
        imode = 0;
    }
    else {
      continue;
    }
    // boost to B rest frame
    LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(B.mom().betaVec());
    FourMomentum pOnium = boost.transform(onium.mom());
    FourMomentum pKstar = boost.transform(Kstar.mom());
    FourMomentum pK = boost.transform(K.mom());
    // axes
    Vector3 axisX = pOnium.p3().unit();
    // kaon helicity angle
    LorentzTransform boostK = LorentzTransform::mkFrameTransformFromBeta(pKstar.betaVec());
    double cosK = -axisX.dot(boostK.transform(pK).p3().unit());
    _h[imode]->fill(cosK);
  }
}


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

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h[3];
/// @}

};

RIVET_DECLARE_PLUGIN(CLEO_2001_I535113);

} ```