Rivet analyses

title: BABAR_2007_I748372

Measurement of angular distributions in $B\to K^* + J/\psi, \psi(2S)$ and $\chi_{c1}$ decays

Experiment: BABAR (PEP-II)

Inspire ID: 748372

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 76 (2007) 031102

Beams: * *

Beam energies: ANY

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

Measurement of the $K^$ helicity angle and transversality angles in the charmonium decay for $B\to K^ + J/\psi, \psi(2S)$ and $\chi_{c1}$ decays. The data were read from Figure 2 in the paper which are corrected for efficiency/acceptance.

Source code:BABAR_2007_I748372.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief B -> K* J/psi, psi(2S) and chi_c1 class BABAR_2007_I748372 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2007_I748372);


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

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

bool isOnium(int pid) const {
  return pid == 443 || pid == 100443 || pid == 20443;
}

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 (isOnium(B.children()[0].abspid()) && isKstar(B.children()[1].abspid())) {
      onium = B.children()[0];
      Kstar = B.children()[1];
    }
    else if (isOnium(B.children()[1].abspid()) && isKstar(B.children()[0].abspid())) {
      onium = B.children()[1];
      Kstar = B.children()[0];
    }
    else
      continue;
    if (onium.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;
    int iK = -1;
    if (B.abspid() == 511) {
      if (K.abspid() == 321)
        iK = 0;
      else
        continue;
    }
    else {
      if (K.abspid() == 321)
        iK = 2;
      else
        iK = 1;
    }
    // find onium decay products
    Particle oDec;
    if (onium.pid() == 20443) {
      if (onium.children()[0].pid() == 443 && onium.children()[1].pid() == 22) {
        oDec = onium.children()[0];
      }
      else if (onium.children()[1].pid() == 443 && onium.children()[0].pid() == 22) {
        oDec = onium.children()[1];
      }
      else
        continue;
    }
    else {
      if (onium.children()[0].pid() == -13 && onium.children()[1].pid() == 13) {
        oDec = onium.children()[1];
      }
      else if (onium.children()[1].pid() == -13 && onium.children()[0].pid() == 13) {
        oDec = onium.children()[0];
      }
      else if (onium.children()[0].pid() == -11 && onium.children()[1].pid() == 11) {
        oDec = onium.children()[1];
      }
      else if (onium.children()[1].pid() == -11 && onium.children()[0].pid() == 11) {
        oDec = onium.children()[0];
      }
      else
        continue;
    }
    // boost to B rest frame
    LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(B.momentum().betaVec());
    FourMomentum pOnium = boost.transform(onium.momentum());
    FourMomentum pKstar = boost.transform(Kstar.momentum());
    FourMomentum pK = boost.transform(K.momentum());
    FourMomentum pOdec = boost.transform(oDec.momentum());
    // axes
    Vector3 axisX = pOnium.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(pOnium.betaVec());
    Vector3 axisL = boostL.transform(pOdec).p3().unit();
    double cosL = axisL.dot(axisZ);
    double phiL = atan2(axisL.dot(axisY), axisL.dot(axisX));
    if (phiL < 0.) phiL += 2. * M_PI;
    // fill hists
    int iloc = onium.pid() == 443 ? 0 : (onium.pid() == 100443 ? 1 : 2);
    _h[0][iloc][iK]->fill(cosK);
    _h[1][iloc][iK]->fill(cosL);
    _h[2][iloc][iK]->fill(phiL);
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  for (unsigned int ix = 0; ix < 3; ++ix)
    for (unsigned int iy = 0; iy < 3; ++iy)
      for (unsigned int iz = 0; iz < 3; ++iz) normalize(_h[ix][iy][iz], 1., false);
}

/// @}


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

};

RIVET_DECLARE_PLUGIN(BABAR_2007_I748372);

} ```