Rivet analyses

title: BABAR_2006_I722820

Mass and helicity angle distributions in $B\to\eta K^*$

Experiment: BABAR (PEP-II)

Inspire ID: 722820

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.Lett. 97 (2006) 201802

Beams: * *

Beam energies: ANY

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

Measurement of the $K\pi$ mass and helicity angle in $B\to\eta K^*$ decays. The data were read from Figure 2 in the paper and the backgrounds given subtracted.

Source code:BABAR_2006_I722820.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief B -> eta K* class BABAR_2006_I722820 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2006_I722820);


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

/// Book histograms and initialise projections before the run
void init() {
  // projection
  UnstableParticles ufs = UnstableParticles(Cuts::abspid == 511 || Cuts::abspid == 521);
  declare(ufs, "UFS");
  DecayedParticles BB(ufs);
  BB.addStable(PID::ETA);
  BB.addStable(PID::K0S);
  BB.addStable(PID::PI0);
  declare(BB, "BB");
  // histograms
  for (unsigned int ix = 0; ix < 2; ++ix)
    for (unsigned int iy = 0; iy < 2; ++iy) book(_h[ix][iy], 1, 1 + ix, 1 + iy);
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  static const map<PdgId, unsigned int>& mode1 = {{321, 1}, {-211, 1}, {221, 1}};
  static const map<PdgId, unsigned int>& mode1CC = {{-321, 1}, {211, 1}, {221, 1}};
  static const map<PdgId, unsigned int>& mode2 = {{321, 1}, {111, 1}, {221, 1}};
  static const map<PdgId, unsigned int>& mode2CC = {{-321, 1}, {111, 1}, {221, 1}};
  static const map<PdgId, unsigned int>& mode3 = {{310, 1}, {211, 1}, {221, 1}};
  static const map<PdgId, unsigned int>& mode3CC = {{310, 1}, {-211, 1}, {221, 1}};
  DecayedParticles BB = apply<DecayedParticles>(event, "BB");
  // loop over particles
  for (unsigned int ix = 0; ix < BB.decaying().size(); ++ix) {
    int imode = 1, iK = 321, iPi = -211;
    if (BB.decaying()[ix].pid() > 0 && BB.modeMatches(ix, 3, mode1)) {
      imode = 0;
      iK = 321;
      iPi = -211;
    }
    else if (BB.decaying()[ix].pid() < 0 && BB.modeMatches(ix, 3, mode1CC)) {
      imode = 0;
      iK = -321;
      iPi = 211;
    }
    else if (BB.decaying()[ix].pid() > 0 && BB.modeMatches(ix, 3, mode2)) {
      iK = 321;
      iPi = 111;
    }
    else if (BB.decaying()[ix].pid() < 0 && BB.modeMatches(ix, 3, mode2CC)) {
      iK = -321;
      iPi = 111;
    }
    else if (BB.decaying()[ix].pid() > 0 && BB.modeMatches(ix, 3, mode3)) {
      iK = 310;
      iPi = 211;
    }
    else if (BB.decaying()[ix].pid() < 0 && BB.modeMatches(ix, 3, mode3CC)) {
      iK = 310;
      iPi = -211;
    }
    else
      continue;
    const Particle& KK = BB.decayProducts()[ix].at(iK)[0];
    const Particle& pi = BB.decayProducts()[ix].at(iPi)[0];
    double mKpi = (KK.momentum() + pi.momentum()).mass();
    _h[0][imode]->fill(mKpi);
    // boost to b rest frame
    LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(
        BB.decaying()[ix].momentum().betaVec());
    FourMomentum pK = boost1.transform(KK.momentum());
    FourMomentum ppi = boost1.transform(pi.momentum());
    FourMomentum pKS = pK + ppi;
    LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pKS.betaVec());
    Vector3 axis = pKS.p3().unit();
    _h[1][imode]->fill(axis.dot(boost2.transform(pK).p3().unit()));
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  for (unsigned int ix = 0; ix < 2; ++ix)
    for (unsigned int iy = 0; iy < 2; ++iy) normalize(_h[ix][iy], 1., false);
}

/// @}


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

};

RIVET_DECLARE_PLUGIN(BABAR_2006_I722820);

} ```