Rivet analyses

title: ARGUS_1994_I376001

Helicity angles in $B\to J/\psi K^{*}$

Experiment: ARGUS (DORIS)

Inspire ID: 376001

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Lett.B 340 (1994) 217-220

Beams: * *

Beam energies: ANY

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

Measurement of the $K^$ and $J/\psi$ helicity angles in the charmonium decay for $B\to J/\psi K^{}$. The data were read from Figure 2 in the paper which are background subtracted and corrected for efficiency/acceptance.

Source code:ARGUS_1994_I376001.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief B -> J/psi K* class ARGUS_1994_I376001 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(ARGUS_1994_I376001);


/// @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");
  // histograms
  for (unsigned int iz = 0; iz < 2; ++iz) {
    book(_h[iz], 1, 1, 1 + iz);
  }
}

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 jPsi, Kstar;
    if (B.children()[0].pid() == 443 && isKstar(B.children()[1].abspid())) {
      jPsi = B.children()[0];
      Kstar = B.children()[1];
    }
    else if (B.children()[1].pid() == 443 && isKstar(B.children()[0].abspid())) {
      jPsi = B.children()[1];
      Kstar = B.children()[0];
    }
    else {
      continue;
    }
    if (jPsi.children().size() != 2) 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;
    }
    // find jPsi decay products
    Particle oDec;
    if (jPsi.children()[0].pid() == -13 && jPsi.children()[1].pid() == 13) {
      oDec = jPsi.children()[1];
    }
    else if (jPsi.children()[1].pid() == -13 && jPsi.children()[0].pid() == 13) {
      oDec = jPsi.children()[0];
    }
    else if (jPsi.children()[0].pid() == -11 && jPsi.children()[1].pid() == 11) {
      oDec = jPsi.children()[1];
    }
    else if (jPsi.children()[1].pid() == -11 && jPsi.children()[0].pid() == 11) {
      oDec = jPsi.children()[0];
    }
    else {
      continue;
    }
    // boost to B rest frame
    LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(B.mom().betaVec());
    FourMomentum pJPsi = boost.transform(jPsi.mom());
    FourMomentum pKstar = boost.transform(Kstar.mom());
    FourMomentum pK = boost.transform(K.mom());
    FourMomentum pOdec = boost.transform(oDec.mom());
    // axes
    Vector3 axisX = pJPsi.p3().unit();
    Vector3 axisY = (pK.p3() - axisX.dot(pK.p3()) * axisX).unit();
    Vector3 axisZ = axisX.cross(axisY).unit();
    // kaon helicity angle
    LorentzTransform boostK = LorentzTransform::mkFrameTransformFromBeta(pKstar.betaVec());
    double cosK = -axisX.dot(boostK.transform(pK).p3().unit());
    // transversality angles
    LorentzTransform boostL = LorentzTransform::mkFrameTransformFromBeta(pJPsi.betaVec());
    Vector3 axisL = boostL.transform(pOdec).p3().unit();
    double cosL = axisL.dot(axisZ);
    // fill hists
    _h[0]->fill(cosL);
    _h[1]->fill(cosK);
  }
}


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

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h[2];
/// @}

};

RIVET_DECLARE_PLUGIN(ARGUS_1994_I376001);

} ```