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/DecayedParticles.hh"
#include "Rivet/Projections/UnstableParticles.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);

}