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BABAR_2008_I758167

Helicity angles in $B\to \bar{D} D_{s1}^+(2536)$, $B\to \psi(3770)K$ and $B\to X(3872)K$
Experiment: BABAR (PEP-II)
Inspire ID: 758167
Status: VALIDATED NOHEPDATA
Authors:
  • Peter Richardson
References:
  • Phys.Rev.D 77 (2008) 011102
Beams: * *
Beam energies: ANY
Run details:
  • Any process producing B mesons, originally Upsilon(4S)

Measurement of helicity angles in $B\to \bar{D} D_{s1}^+(2536)$, $B\to \psi(3770)K$ and $B\to X(3872)K$ decays using $B\to \bar{D}^{(*)}D^{(*)}K$ modes. The background subtracted, efficiency corrected distributions were read from Figure 1 in the paper. There is no consensus as to the nature of the $X(3872)$ $c\bar{c}$ state and therefore we taken its PDG code to be 9030443, i.e. the first unused code for an undetermined spin one $c\bar{c}$ state. This can be changed using the PID option if a different code is used by the event generator performing the simulation.

Source code: BABAR_2008_I758167.cc
  1// -*- C++ -*-
  2#include "Rivet/Analysis.hh"
  3#include "Rivet/Projections/UnstableParticles.hh"
  4
  5namespace Rivet {
  6
  7
  8  /// @brief B -> D(*) D(*) K
  9  class BABAR_2008_I758167 : public Analysis {
 10  public:
 11
 12    /// Constructor
 13    RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2008_I758167);
 14
 15
 16    /// @name Analysis methods
 17    /// @{
 18
 19    /// Book histograms and initialise projections before the run
 20    void init() {
 21      // set the PDG code
 22      _pid = getOption<int>("PID", 9030443);
 23      // Initialise and register projections
 24      UnstableParticles ufs = UnstableParticles(Cuts::abspid==511 ||
 25						Cuts::abspid==521);
 26      declare(ufs, "UFS");
 27      // histos
 28      for(unsigned int ix=0;ix<3;++ix)
 29	book(_h[ix],1,1,1+ix);
 30    }
 31
 32    bool isK(int id) {
 33      return id==321 || id==311 || id==310 || id==130; 
 34    }
 35
 36    /// Perform the per-event analysis
 37    void analyze(const Event& event) {
 38      UnstableParticles ufs = apply<UnstableParticles>(event,"UFS");
 39      for(const Particle & B : ufs.particles()) {
 40	if(B.children().size()!=2) continue;
 41	int sign = B.pid()/B.abspid(), iD = B.abspid()-100;
 42	unsigned int imode=0;
 43	// boost to B rest frame
 44	LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(B.momentum().betaVec());
 45	Particle resonance;
 46	if(B.children()[0].pid()== sign*10433 &&
 47	   B.children()[1].pid()==-sign*iD) {
 48	  imode=0;
 49	  resonance=B.children()[0];
 50	}
 51	else if(B.children()[1].pid()== sign*10433 &&
 52		B.children()[0].pid()==-sign*iD) {
 53	  imode=0;
 54	  resonance=B.children()[1];
 55	}
 56	else if(B.children()[0].pid()== 30443 &&
 57		isK(B.children()[1].pid())) {
 58	  imode=1;
 59	  resonance=B.children()[0];
 60	}
 61	else if(B.children()[1].pid()== 30443 &&
 62		isK(B.children()[0].pid())) {
 63	  imode=1;
 64	  resonance=B.children()[1];
 65	}
 66	else if(B.children()[0].pid()== _pid &&
 67		isK(B.children()[1].pid())) {
 68	  imode=2;
 69	  resonance=B.children()[0];
 70	}
 71	else if(B.children()[1].pid()== _pid &&
 72		isK(B.children()[0].pid())) {
 73	  imode=2;
 74	  resonance=B.children()[1];
 75	}
 76	else
 77	  continue;
 78	if(resonance.children().size()!=2) continue;
 79	FourMomentum pRes = boost1.transform(resonance.momentum());
 80	LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pRes.betaVec());
 81	Vector3 axis1 = -pRes.p3().unit();
 82	Particle child;
 83	if(imode==0) {
 84	  Particle Dstar;
 85	  if(isK(resonance.children()[1].pid()) &&
 86	     (resonance.children()[0].pid()==sign*413 || resonance.children()[0].pid()==sign*423))
 87	    child = resonance.children()[0];
 88	  else if(isK(resonance.children()[0].pid()) &&
 89		  (resonance.children()[1].pid()==sign*413 || resonance.children()[1].pid()==sign*423))
 90	    child = resonance.children()[1];
 91	  else
 92	    continue;
 93	}
 94	// B -> D psi(3770)
 95	else if(imode==1) {
 96	  if(resonance.children()[0].pid()!=-resonance.children()[1].pid()) continue;
 97	  if(resonance.children()[0].abspid()!=411 &&
 98	     resonance.children()[0].abspid()!=421) continue;
 99	  child = resonance.children()[0].pid()>0 ? resonance.children()[0] : resonance.children()[1];
100	}
101	else if(imode==2) {
102	  if( (resonance.children()[0].abspid()==423 && resonance.children()[1].abspid()==421) ||
103	      (resonance.children()[1].abspid()==423 && resonance.children()[0].abspid()==421)) {
104	    child = resonance.children()[0].pid()>0 ? resonance.children()[0] : resonance.children()[1];
105	  }
106	  else continue;
107	}
108	Vector3 axis2 = boost2.transform(boost1.transform(child.momentum())).p3().unit();
109	_h[imode]->fill(axis1.dot(axis2));
110      }
111    }
112
113
114    /// Normalise histograms etc., after the run
115    void finalize() {
116      for(unsigned int ix=0;ix<3;++ix)
117	normalize(_h[ix],1.,false);
118    }
119
120    /// @}
121
122
123    /// @name Histograms
124    /// @{
125    int _pid;
126    Histo1DPtr _h[3];
127    /// @}
128
129
130  };
131
132
133  RIVET_DECLARE_PLUGIN(BABAR_2008_I758167);
134
135}