Rivet analyses

Helicity angle in B− → D0K*−

Experiment: BABAR (PEP-II)

Inspire ID: 714147

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 73 (2006) 111104

Beams: * *

Beam energies: ANY

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

Measurement of the Helicity angle in B− → D0K*−. The acceptance corrected data was read from Figure 2 in the paper and the background given subtracted.

Source code:BABAR_2006_I714147.cc

// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/UnstableParticles.hh"
#include "Rivet/Projections/DecayedParticles.hh"

namespace Rivet {


  /// @brief B- -> D0 K*-
  class BABAR_2006_I714147 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2006_I714147);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // projection
      UnstableParticles ufs = UnstableParticles(Cuts::abspid==521);
      declare(ufs, "UFS");
      // hists
      book(_h,1,1,1);
    }

    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;
    int sign = B.pid()/B.abspid();
    Particle D,Kstar;
    if(B.children()[0].pid()==-sign*421 &&
       isKstar(B.children()[1].abspid())) {
      D     = B.children()[0];
      Kstar = B.children()[1];
    }
    else if(B.children()[1].pid()==-sign*421 &&
        isKstar(B.children()[0].abspid())) {
      D     = B.children()[1];
      Kstar = B.children()[0];
    }
    else
      continue;
    // find Kstar decay products
    Particle pi;
    if(isK (Kstar.children()[0].abspid()) &&
       isPi(Kstar.children()[1].abspid())) {
      pi = Kstar.children()[1];
    }
    else if(isK (Kstar.children()[1].abspid()) &&
        isPi(Kstar.children()[0].abspid())) {
      pi = Kstar.children()[0];
    }
    else
      continue;
    // boost to B rest frame
    LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(B.momentum().betaVec());
    FourMomentum pD     = boost.transform(D    .momentum());
    FourMomentum pKstar = boost.transform(Kstar.momentum());
    FourMomentum pPi     = boost.transform(pi   .momentum());
    // pion helicity angle
    Vector3 axisX = pD.p3().unit();
    LorentzTransform boostK = LorentzTransform::mkFrameTransformFromBeta(pKstar.betaVec());
    double cosPi = -axisX.dot(boostK.transform(pPi).p3().unit());
    _h->fill(cosPi);
      }
    }


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

    /// @}


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


  };


  RIVET_DECLARE_PLUGIN(BABAR_2006_I714147);

}