Rivet analyses

Helicity angles and Polarization in B0 → Ds*+D*−

Experiment: BABAR (PEP-II)

Inspire ID: 613283

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 67 (2003) 092003

Beams: * *

Beam energies: ANY

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

Measurement of the helicity angles and polarization in B0 → Ds*+D*−. The polarization was given in the paper and the background subtracted data for the helicity angles was extracted from figure 2 in the paper.

Source code:BABAR_2003_I613283.cc

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

namespace Rivet {


  /// @brief B0 -> Ds* D*
  class BABAR_2003_I613283 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2003_I613283);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      UnstableParticles ufs = UnstableParticles(Cuts::abspid == 511);
      declare(ufs, "UFS");
      DecayedParticles B0(ufs);
      B0.addStable(413);
      B0.addStable(-413);
      B0.addStable(433);
      B0.addStable(-433);
      declare(B0, "B0");
      // histos
      for (unsigned int ix = 0; ix < 2; ++ix) book(_h[ix], 2, 1 + ix, 1);
      for (unsigned int ix = 0; ix < 2; ++ix) book(_p[ix], "TMP/p_" + toString(ix + 1));
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      static const map<PdgId, unsigned int>& mode = {{433, 1}, {-413, 1}};
      static const map<PdgId, unsigned int>& modeCC = {{-433, 1}, {413, 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, 2, mode))
          sign = 1.;
        else if (B0.decaying()[ix].pid() < 0 && B0.modeMatches(ix, 2, modeCC))
          sign = -1.;
        else
          continue;
        // find D* decay products
        const Particle& Dstar = B0.decayProducts()[ix].at(-sign * 413)[0];
        if (Dstar.children().size() != 2) continue;
        Particle pim;
        if (Dstar.children()[0].pid() == -sign * 211 && Dstar.children()[1].pid() == -sign * 421) {
          pim = Dstar.children()[0];
        }
        else if (Dstar.children()[1].pid() == -sign * 211 && Dstar.children()[0].pid() == -sign * 421) {
          pim = Dstar.children()[1];
        }
        else
          continue;
        // find Ds* decay products
        const Particle& DSstar = B0.decayProducts()[ix].at(sign * 433)[0];
        Particle gamma;
        if (DSstar.children()[0].pid() == 22 && DSstar.children()[1].pid() == sign * 431) {
          gamma = DSstar.children()[0];
        }
        else if (DSstar.children()[1].pid() == 22 && DSstar.children()[0].pid() == sign * 431) {
          gamma = DSstar.children()[1];
        }
        else
          continue;
        // boost to B rest frame
        LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(
            B0.decaying()[ix].momentum().betaVec());
        FourMomentum pDSstar = boost.transform(DSstar.momentum());
        FourMomentum pDstar = boost.transform(Dstar.momentum());
        FourMomentum pGamma = boost.transform(gamma.momentum());
        FourMomentum pPim = boost.transform(pim.momentum());
        const LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pDstar.betaVec());
        pPim = boost2.transform(pPim);
        double cPi = pPim.p3().unit().dot(pDSstar.p3().unit());
        const LorentzTransform boost3 = LorentzTransform::mkFrameTransformFromBeta(pDSstar.betaVec());
        pGamma = boost3.transform(pGamma);
        double cGamma = pGamma.p3().unit().dot(pDstar.p3().unit());
        _p[0]->fill(-100. * (1. - 5. * sqr(cPi)) / 2.);
        _p[1]->fill();
        _h[0]->fill(cPi);
        _h[1]->fill(cGamma);
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      for (unsigned int ix = 0; ix < 2; ++ix) normalize(_h[ix], 1., false);
      Estimate0DPtr tmp;
      book(tmp, 1, 1, 1);
      divide(*_p[0], *_p[1], tmp);
    }

    /// @}


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


  RIVET_DECLARE_PLUGIN(BABAR_2003_I613283);

}