Rivet analyses

title: BABAR_2005_I667017

Helicity angle in $B^0\to D^\mp K^{*\pm}$

Experiment: BABAR (PEP-II)

Inspire ID: 667017

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.Lett. 95 (2005) 171802

Beams: * *

Beam energies: ANY

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

Measurement of the helicity angle in $B^0\to D^\mp K^{*\pm}$ decays. The efficiency corrected, background subtracted decay were read from figure 3 in the paper.

Source code:BABAR_2005_I667017.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief B0 -> D-+ K*+- class BABAR_2005_I667017 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2005_I667017);


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

/// Book histograms and initialise projections before the run
void init() {
  // projection
  UnstableParticles ufs = UnstableParticles(Cuts::abspid == 511);
  declare(ufs, "UFS");
  // hists
  book(_h, 1, 1, 1);
}

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;
    int sign = B.pid() / B.abspid();
    Particle Kstar;
    if (B.children()[0].pid() == -sign * 411 && B.children()[1].pid() == sign * 323) {
      Kstar = B.children()[1];
    }
    else if (B.children()[1].pid() == -sign * 411 && B.children()[0].pid() == sign * 323) {
      Kstar = B.children()[0];
    }
    else
      continue;
    // find Kstar decay products
    Particle KK;
    if (isK(Kstar.children()[0].abspid()) && isPi(Kstar.children()[1].abspid())) {
      KK = Kstar.children()[0];
    }
    else if (isK(Kstar.children()[1].abspid()) && isPi(Kstar.children()[0].abspid())) {
      KK = Kstar.children()[1];
    }
    else
      continue;
    // boost to B rest frame
    LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(B.momentum().betaVec());
    FourMomentum pKstar = boost.transform(Kstar.momentum());
    FourMomentum pK = boost.transform(KK.momentum());
    // kaon helicity angle
    Vector3 axisX = pKstar.p3().unit();
    LorentzTransform boostK = LorentzTransform::mkFrameTransformFromBeta(pKstar.betaVec());
    double cosK = axisX.dot(boostK.transform(pK).p3().unit());
    _h->fill(cosK);
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  normalize(_h, 1., false);
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h;
/// @}

};

RIVET_DECLARE_PLUGIN(BABAR_2005_I667017);

} ```