Rivet analyses

title: BABAR_2007_I722710

$B^0\to\eta^\prime K^{*0}$ decays

Experiment: BABAR (PEP-II)

Inspire ID: 722710

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.Lett. 98 (2007) 051802

Beams: * *

Beam energies: ANY

Run details: - Any process producing B0, originally Upsilon(4S) decay

Measurement of the $K^{0}$ mass and helicity angle distributions for $B^0\to\eta^\prime K^{0}$ by Babar. The data was read from the plots in the paper which are however background subtracted and efficiency corrected.

Source code:BABAR_2007_I722710.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief B0 -> K*0 eta' class BABAR_2007_I722710 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2007_I722710);


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

/// Book histograms and initialise projections before the run
void init() {
  // projection
  UnstableParticles ufs = UnstableParticles(Cuts::abspid == 511);
  declare(ufs, "UFS");
  DecayedParticles B0(ufs);
  B0.addStable(PID::ETAPRIME);
  declare(B0, "B0");
  // histograms
  for (unsigned int ix = 0; ix < 2; ++ix) book(_h[ix], ix + 1, 1, 1);
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  static const map<PdgId, unsigned int>& mode = {{321, 1}, {-211, 1}, {331, 1}};
  static const map<PdgId, unsigned int>& modeCC = {{-321, 1}, {211, 1}, {331, 1}};
  DecayedParticles B0 = apply<DecayedParticles>(event, "B0");
  // loop over particles
  for (unsigned int ix = 0; ix < B0.decaying().size(); ++ix) {
    int sign = 1;
    if (B0.decaying()[ix].pid() > 0 && B0.modeMatches(ix, 3, mode)) {
      sign = 1;
    }
    else if (B0.decaying()[ix].pid() < 0 && B0.modeMatches(ix, 3, modeCC)) {
      sign = -1;
    }
    else
      continue;
    const Particle& Kp = B0.decayProducts()[ix].at(sign * 321)[0];
    const Particle& pim = B0.decayProducts()[ix].at(-sign * 211)[0];
    double mKpi = (Kp.momentum() + pim.momentum()).mass();
    if (mKpi < .755 || mKpi > 1.305) continue;
    _h[0]->fill(mKpi);
    // boost to b rest frame
    LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(
        B0.decaying()[ix].momentum().betaVec());
    FourMomentum pK = boost1.transform(Kp.momentum());
    FourMomentum ppi = boost1.transform(pim.momentum());
    FourMomentum pKS = pK + ppi;
    LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pKS.betaVec());
    Vector3 axis = pKS.p3().unit();
    _h[1]->fill(axis.dot(boost2.transform(pK).p3().unit()));
  }
}


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

/// @}


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

};

RIVET_DECLARE_PLUGIN(BABAR_2007_I722710);

} ```