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BELLE_2017_I1512299

Decay kinematics of semileptonc $\bar{B}^0\to D^{*+}$ decays.
Experiment: BELLE (KEKB)
Inspire ID: 1512299
Status: VALIDATED
Authors:
  • Holger Schulz
No references listed
Beams: * *
Beam energies: ANY
Run details:
  • Semileptonic B0bar (-511) decays.

Unfolded measurement of recoil w, helicity and decay plane angles of semileptonc $\bar{B}^0$ to $D^{*+}$ decays. The data was used to determine $V_{cb}$. Note that the data in the paper does not account for the bin widths. The data shipped with rivet is divided by the bin width and all curves are normalised to the partial width of $\bar{B}^0\to D^{*+} \ell \nu_\ell$

Source code: BELLE_2017_I1512299.cc
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// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {


  /// @brief Bbar0 -> D*+ semileptonic
  class BELLE_2017_I1512299 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2017_I1512299);


    /// @name Analysis methods
    //@{

    /// Book histograms and initialise projections before the run
    void init() {

      // Initialise and register projections
      declare(UnstableParticles(), "UFS");

      // Book histograms
      book(_h_w     , 1, 1, 1);
      book(_h_costhv, 2, 1, 1);
      book(_h_costhl, 3, 1, 1);
      book(_h_chi   , 4, 1, 1);

    }


    /// Perform the per-event analysis
    bool analyzeDecay(Particle mother, vector<int> ids) {
      // There is no point in looking for decays with less particles than to be analysed
      if (mother.children().size() == ids.size()) {
        bool decayfound = true;
        for (int id : ids) {
          if (!contains(mother, id)) decayfound = false;
        }
        return decayfound;
      }
      return false;
    }

    bool contains(Particle& mother, int id) {
      return any(mother.children(), HasPID(id));
    }


    double recoilW(const Particle& mother) {
      FourMomentum lepton, neutrino, meson, q;
      for(const Particle& c : mother.children()) {
        if (c.isNeutrino()) neutrino=c.mom();
        if (c.isLepton() && !c.isNeutrino()) lepton =c.mom();
        if (c.isHadron()) meson=c.mom();
      }
      q = lepton + neutrino; //no hadron before
      double mb2= mother.mom()*mother.mom();
      double mD2 = meson*meson;
      return (mb2 + mD2 - q*q )/ (2. * sqrt(mb2) * sqrt(mD2) );
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      FourMomentum pl, pnu, pB, pD, pDs, ppi;
      // Iterate of B0bar mesons
      for(const Particle& p : apply<UnstableParticles>(event, "UFS").particles(Cuts::pid==-511)) {
        pB = p.momentum();
        // Find semileptonic decays
        if (analyzeDecay(p, {PID::DSTARPLUS,-12,11}) || analyzeDecay(p, {PID::DSTARPLUS,-14,13}) ) {
          _h_w->fill(recoilW(p));
          // Get the necessary momenta for the angles
          bool foundDdecay=false;
          for (const Particle & c : p.children()) {
            if ( (c.pid() == PID::DSTARPLUS)  && (analyzeDecay(c, {PID::PIPLUS, PID::D0}) || analyzeDecay(c, {PID::PI0, PID::DPLUS})) ) {
              foundDdecay=true;
              pDs = c.momentum();
              for (const Particle & dc : c.children()) {
                if (dc.hasCharm()) pD = dc.momentum();
                else ppi = dc.momentum();
              }
            }
            if (c.pid() ==  11 || c.pid() ==  13) pl  = c.momentum();
            if (c.pid() == -12 || c.pid() == -14) pnu = c.momentum();
          }
          // This is the angle analysis
          if (foundDdecay) {

            // First boost all relevant momenta into the B-rest frame
            const LorentzTransform B_boost = LorentzTransform::mkFrameTransformFromBeta(pB.betaVec());
            // Momenta in B rest frame
            FourMomentum lv_brest_Dstar = B_boost.transform(pDs);
            FourMomentum lv_brest_w     = B_boost.transform(pB - pDs);
            FourMomentum lv_brest_D     = B_boost.transform(pD);
            FourMomentum lv_brest_lep   = B_boost.transform(pl);
            
            const LorentzTransform Ds_boost = LorentzTransform::mkFrameTransformFromBeta(lv_brest_Dstar.betaVec());
            FourMomentum lv_Dstarrest_D     = Ds_boost.transform(lv_brest_D);
            const LorentzTransform W_boost  = LorentzTransform::mkFrameTransformFromBeta(lv_brest_w.betaVec());
            FourMomentum lv_wrest_lep       = W_boost.transform(lv_brest_lep);

            double cos_thetaV = cos(lv_brest_Dstar.p3().angle(lv_Dstarrest_D.p3()));
            _h_costhv->fill(cos_thetaV);

            double cos_thetaL = cos(lv_brest_w.p3().angle(lv_wrest_lep.p3()));
            _h_costhl->fill(cos_thetaL);

            Vector3 LTrans = lv_wrest_lep.p3()   - cos_thetaL*lv_wrest_lep.p3().perp()*lv_brest_w.p3().unit();
            Vector3 VTrans = lv_Dstarrest_D.p3() - cos_thetaV*lv_Dstarrest_D.p3().perp()*lv_brest_Dstar.p3().unit();
            float chi = atan2(LTrans.cross(VTrans).dot(lv_brest_w.p3().unit()), LTrans.dot(VTrans));
            if(chi < 0) chi += TWOPI;

            _h_chi->fill(chi);
          }
        }
      }
    }
        //else if (analyzeDecay(p, {413,-14,13}) ) {
          //_h_w->fill(recoilW(p));
        //}

    /// Normalise histograms etc., after the run
    void finalize() {

      double GAMMA_B0 = 4.32e-13; // Total width in GeV, calculated from mean life time of 1.52 pico seconds
      double BR_B0_DSPLUS_ELL_NU = 0.0495; // Branching fraction from the same paper for B0bar to D*+ ell nu
      double NORM = GAMMA_B0 * BR_B0_DSPLUS_ELL_NU; // Normalise histos to partial width
      normalize(_h_w,      NORM);
      normalize(_h_costhv, NORM);
      normalize(_h_costhl, NORM);
      normalize(_h_chi,    NORM);
    }

    //@}


    /// @name Histograms
    //@{
    Histo1DPtr _h_w;
    Histo1DPtr _h_costhv;
    Histo1DPtr _h_costhl;
    Histo1DPtr _h_chi;
    //@}


  };


  // The hook for the plugin system
  RIVET_DECLARE_PLUGIN(BELLE_2017_I1512299);


}