rivet is hosted by Hepforge, IPPP Durham

Rivet analyses reference

BELLE_2017_I1512299

Decay kinematics of semileptonc B0bar 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 B0bar to D*+ decays. The data was used to determine Vcb. Note that the data in the paper does not account for the bin wodths. The data shipped with rivet is divided by the bin width and all curves are normalised to the partial width of B0bar-> D*+ ell nu

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 Add a short analysis description here
 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);//lab2brest(gp_Dstar.particle.p());
 96            FourMomentum lv_brest_w     = B_boost.transform(pB - pDs); //lab2brest(p_lv_w);
 97            FourMomentum lv_brest_D     = B_boost.transform(pD); //lab2brest(gp_D.particle.p());
 98            FourMomentum lv_brest_lep   = B_boost.transform(pl); //lab2brest(gp_lep.p());
 99
100            const LorentzTransform Ds_boost = LorentzTransform::mkFrameTransformFromBeta(pDs.betaVec());
101            FourMomentum lv_Dstarrest_D     = Ds_boost.transform(lv_brest_D);
102            const LorentzTransform W_boost  = LorentzTransform::mkFrameTransformFromBeta((pB-pDs).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            //const LorentzTransform W_boost = LorentzTransform::mkFrameTransformFromBeta((pl+pnu).betaVec());
119            //const LorentzTransform D_boost = LorentzTransform::mkFrameTransformFromBeta((pD+ppi).betaVec());
120
121            //FourMomentum pl_t = FourMomentum(W_boost.transform(pl));
122            //FourMomentum pD_t = FourMomentum(D_boost.transform(pD));
123            //double thetal = (pl+pnu).angle(pl_t);
124            //double thetav = (pD+ppi).angle(pD_t);
125            //_h_costhv->fill(cos(thetav));
126            //_h_costhl->fill(cos(thetal));
127          }
128        }
129      }
130    }
131        //else if (analyzeDecay(p, {413,-14,13}) ) {
132          //_h_w->fill(recoilW(p));
133        //}
134
135    /// Normalise histograms etc., after the run
136    void finalize() {
137
138      double GAMMA_B0 = 4.32e-13; // Total width in GeV, calculated from mean life time of 1.52 pico seconds
139      double BR_B0_DSPLUS_ELL_NU = 0.0495; // Branching fraction from the same paper for B0bar to D*+ ell nu
140      double NORM = GAMMA_B0 * BR_B0_DSPLUS_ELL_NU; // Normalise histos to partial width
141      normalize(_h_w,      NORM);
142      normalize(_h_costhv, NORM);
143      normalize(_h_costhl, NORM);
144      normalize(_h_chi,    NORM);
145    }
146
147    //@}
148
149
150    /// @name Histograms
151    //@{
152    Histo1DPtr _h_w;
153    Histo1DPtr _h_costhv;
154    Histo1DPtr _h_costhl;
155    Histo1DPtr _h_chi;
156    //@}
157
158
159  };
160
161
162  // The hook for the plugin system
163  RIVET_DECLARE_PLUGIN(BELLE_2017_I1512299);
164
165
166}