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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
  1// -*- C++ -*-
  2#include "Rivet/Analysis.hh"
  3#include "Rivet/Projections/FinalState.hh"
  4#include "Rivet/Projections/UnstableParticles.hh"
  5
  6namespace Rivet {
  7
  8
  9  /// @brief Bbar0 -> D*+ semileptonic
 10  class BELLE_2017_I1512299 : public Analysis {
 11  public:
 12
 13    /// Constructor
 14    RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2017_I1512299);
 15
 16
 17    /// @name Analysis methods
 18    /// @{
 19
 20    /// Book histograms and initialise projections before the run
 21    void init() {
 22
 23      // Initialise and register projections
 24      declare(UnstableParticles(), "UFS");
 25
 26      // Book histograms
 27      book(_h_w     , 1, 1, 1);
 28      book(_h_costhv, 2, 1, 1);
 29      book(_h_costhl, 3, 1, 1);
 30      book(_h_chi   , 4, 1, 1);
 31
 32    }
 33
 34
 35    /// Perform the per-event analysis
 36    bool analyzeDecay(Particle mother, vector<int> ids) {
 37      // There is no point in looking for decays with less particles than to be analysed
 38      if (mother.children().size() == ids.size()) {
 39        bool decayfound = true;
 40        for (int id : ids) {
 41          if (!contains(mother, id)) decayfound = false;
 42        }
 43        return decayfound;
 44      }
 45      return false;
 46    }
 47
 48    bool contains(Particle& mother, int id) {
 49      return any(mother.children(), HasPID(id));
 50    }
 51
 52
 53    double recoilW(const Particle& mother) {
 54      FourMomentum lepton, neutrino, meson, q;
 55      for(const Particle& c : mother.children()) {
 56        if (c.isNeutrino()) neutrino=c.mom();
 57        if (c.isLepton() && !c.isNeutrino()) lepton =c.mom();
 58        if (c.isHadron()) meson=c.mom();
 59      }
 60      q = lepton + neutrino; //no hadron before
 61      double mb2= mother.mom()*mother.mom();
 62      double mD2 = meson*meson;
 63      return (mb2 + mD2 - q*q )/ (2. * sqrt(mb2) * sqrt(mD2) );
 64    }
 65
 66    /// Perform the per-event analysis
 67    void analyze(const Event& event) {
 68      FourMomentum pl, pnu, pB, pD, pDs, ppi;
 69      // Iterate of B0bar mesons
 70      for(const Particle& p : apply<UnstableParticles>(event, "UFS").particles(Cuts::pid==-511)) {
 71        pB = p.momentum();
 72        // Find semileptonic decays
 73        if (analyzeDecay(p, {PID::DSTARPLUS,-12,11}) || analyzeDecay(p, {PID::DSTARPLUS,-14,13}) ) {
 74          _h_w->fill(recoilW(p));
 75          // Get the necessary momenta for the angles
 76          bool foundDdecay=false;
 77          for (const Particle & c : p.children()) {
 78            if ( (c.pid() == PID::DSTARPLUS)  && (analyzeDecay(c, {PID::PIPLUS, PID::D0}) || analyzeDecay(c, {PID::PI0, PID::DPLUS})) ) {
 79              foundDdecay=true;
 80              pDs = c.momentum();
 81              for (const Particle & dc : c.children()) {
 82                if (dc.hasCharm()) pD = dc.momentum();
 83                else ppi = dc.momentum();
 84              }
 85            }
 86            if (c.pid() ==  11 || c.pid() ==  13) pl  = c.momentum();
 87            if (c.pid() == -12 || c.pid() == -14) pnu = c.momentum();
 88          }
 89          // This is the angle analysis
 90          if (foundDdecay) {
 91
 92            // First boost all relevant momenta into the B-rest frame
 93            const LorentzTransform B_boost = LorentzTransform::mkFrameTransformFromBeta(pB.betaVec());
 94            // Momenta in B rest frame
 95            FourMomentum lv_brest_Dstar = B_boost.transform(pDs);
 96            FourMomentum lv_brest_w     = B_boost.transform(pB - pDs);
 97            FourMomentum lv_brest_D     = B_boost.transform(pD);
 98            FourMomentum lv_brest_lep   = B_boost.transform(pl);
 99            
100            const LorentzTransform Ds_boost = LorentzTransform::mkFrameTransformFromBeta(lv_brest_Dstar.betaVec());
101            FourMomentum lv_Dstarrest_D     = Ds_boost.transform(lv_brest_D);
102            const LorentzTransform W_boost  = LorentzTransform::mkFrameTransformFromBeta(lv_brest_w.betaVec());
103            FourMomentum lv_wrest_lep       = W_boost.transform(lv_brest_lep);
104
105            double cos_thetaV = cos(lv_brest_Dstar.p3().angle(lv_Dstarrest_D.p3()));
106            _h_costhv->fill(cos_thetaV);
107
108            double cos_thetaL = cos(lv_brest_w.p3().angle(lv_wrest_lep.p3()));
109            _h_costhl->fill(cos_thetaL);
110
111            Vector3 LTrans = lv_wrest_lep.p3()   - cos_thetaL*lv_wrest_lep.p3().perp()*lv_brest_w.p3().unit();
112            Vector3 VTrans = lv_Dstarrest_D.p3() - cos_thetaV*lv_Dstarrest_D.p3().perp()*lv_brest_Dstar.p3().unit();
113            float chi = atan2(LTrans.cross(VTrans).dot(lv_brest_w.p3().unit()), LTrans.dot(VTrans));
114            if(chi < 0) chi += TWOPI;
115
116            _h_chi->fill(chi);
117          }
118        }
119      }
120    }
121        //else if (analyzeDecay(p, {413,-14,13}) ) {
122          //_h_w->fill(recoilW(p));
123        //}
124
125    /// Normalise histograms etc., after the run
126    void finalize() {
127
128      double GAMMA_B0 = 4.32e-13; // Total width in GeV, calculated from mean life time of 1.52 pico seconds
129      double BR_B0_DSPLUS_ELL_NU = 0.0495; // Branching fraction from the same paper for B0bar to D*+ ell nu
130      double NORM = GAMMA_B0 * BR_B0_DSPLUS_ELL_NU; // Normalise histos to partial width
131      normalize(_h_w,      NORM);
132      normalize(_h_costhv, NORM);
133      normalize(_h_costhl, NORM);
134      normalize(_h_chi,    NORM);
135    }
136
137    /// @}
138
139
140    /// @name Histograms
141    /// @{
142    Histo1DPtr _h_w;
143    Histo1DPtr _h_costhv;
144    Histo1DPtr _h_costhl;
145    Histo1DPtr _h_chi;
146    /// @}
147
148
149  };
150
151
152  RIVET_DECLARE_PLUGIN(BELLE_2017_I1512299);
153
154
155}