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LHCB_2012_I1097092

$B_c^+\to J/\psi\pi^+$ and $B_c^+\to J/\psi\pi^+\pi^+\pi^-$
Experiment: LHCB (LHC)
Inspire ID: 1097092
Status: VALIDATED NOHEPDATA
Authors:
  • Peter Richardson
References:
  • Phy.Rev.Lett. 108 (2012) 251802
Beams: * *
Beam energies: ANY
Run details:
  • Any process producing B_c+, originally pp

Angular distributions in between the muons $B_c^+\to J/\psi\pi^+$ and $B_c^+\to J/\psi\pi^+\pi^+\pi^-$ with the muons from $J/\psi\to\mu^+\mu^-$ and mass distributions in $B_c^+\to J/\psi\pi^+\pi^+\pi^-$. The data were read from the plots in the paper and may not be corrected for efficiency and acceptance.

Source code: LHCB_2012_I1097092.cc
  1// -*- C++ -*-
  2#include "Rivet/Analysis.hh"
  3#include "Rivet/Projections/UnstableParticles.hh"
  4#include "Rivet/Projections/DecayedParticles.hh"
  5
  6namespace Rivet {
  7
  8
  9  /// @brief B_c - > jpsi pi+ and pi+pi+pi-
 10  class LHCB_2012_I1097092 : public Analysis {
 11  public:
 12
 13    /// Constructor
 14    RIVET_DEFAULT_ANALYSIS_CTOR(LHCB_2012_I1097092);
 15
 16
 17    /// @name Analysis methods
 18    /// @{
 19
 20    /// Book histograms and initialise projections before the run
 21    void init() {
 22      UnstableParticles ufs = UnstableParticles(Cuts::abspid==541);
 23      declare(ufs, "UFS");
 24      DecayedParticles BC(ufs);
 25      BC.addStable( PID::PI0);
 26      BC.addStable( PID::K0S);
 27      BC.addStable( PID::JPSI);
 28      declare(BC, "BC");
 29      for(unsigned int ix=0;ix<2;++ix) {
 30	book(_h_mass  [ix],1+ix,1,1);
 31	book(_h_ctheta[ix],3,1,1+ix);
 32      }
 33    }
 34
 35
 36    /// Perform the per-event analysis
 37    void analyze(const Event& event) {
 38      static const map<PdgId,unsigned int> & mode1   = { { 443,1}, { 211,1} };
 39      static const map<PdgId,unsigned int> & mode1CC = { { 443,1}, {-211,1} };
 40      static const map<PdgId,unsigned int> & mode2   = { { 443,1}, { 211,2}, {-211,1} };
 41      static const map<PdgId,unsigned int> & mode2CC = { { 443,1}, {-211,2}, { 211,1} };
 42      DecayedParticles BC = apply<DecayedParticles>(event, "BC");
 43      // loop over particles
 44      for(unsigned int ix=0;ix<BC.decaying().size();++ix) {
 45	int sign = BC.decaying()[ix].pid()/BC.decaying()[ix].abspid();
 46	int imode=-1;
 47	if ((sign== 1 && BC.modeMatches(ix,2,mode1  )) ||
 48	    (sign==-1 && BC.modeMatches(ix,2,mode1CC))) {
 49	  imode=0;
 50	}
 51	else if ((sign== 1 && BC.modeMatches(ix,4,mode2  )) ||
 52		 (sign==-1 && BC.modeMatches(ix,4,mode2CC))) {
 53	  const Particle  & pim = BC.decayProducts()[ix].at(-sign*211)[0];
 54	  const Particles & pip = BC.decayProducts()[ix].at( sign*211);
 55	  _h_mass[0]->fill((pim.momentum()+pip[0].momentum()+pip[1].momentum()).mass());
 56	  _h_mass[1]->fill((pim.momentum()+pip[0].momentum()).mass());
 57	  _h_mass[1]->fill((pim.momentum()+pip[1].momentum()).mass());
 58	  imode=1;
 59	}
 60	else
 61	  continue;
 62	// check the J/psi decay mode
 63	const Particle & jpsi = BC.decayProducts()[ix].at(443)[0];
 64	if(jpsi.children().size()!=2 || jpsi.children()[0].pid()!=-jpsi.children()[1].pid() ||
 65	   jpsi.children()[0].abspid()!=13) continue;
 66	Particle muon = jpsi.children()[0].pid()==13 ? jpsi.children()[0] : jpsi.children()[1];
 67	LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(BC.decaying()[ix].momentum().betaVec());
 68	FourMomentum pJPsi = boost1.transform(jpsi.momentum());
 69	FourMomentum pMu   = boost1.transform(muon.momentum());
 70	// to j/psi rest frame
 71	LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pJPsi.betaVec());
 72	Vector3 axis = pJPsi.p3().unit();
 73	FourMomentum pp = boost2.transform(pMu);
 74	// calculate angle
 75	double cTheta = pp.p3().unit().dot(axis);
 76	_h_ctheta[imode]->fill(cTheta);
 77      }
 78    }
 79
 80
 81    /// Normalise histograms etc., after the run
 82    void finalize() {
 83      for(unsigned int ix=0;ix<2;++ix) {
 84	normalize(_h_mass  [ix]);
 85	normalize(_h_ctheta[ix]);
 86      }
 87    }
 88
 89    /// @}
 90
 91
 92    /// @name Histograms
 93    /// @{
 94    Histo1DPtr _h_mass[2];
 95    Histo1DPtr _h_ctheta[2];
 96    /// @}
 97
 98
 99  };
100
101
102  RIVET_DECLARE_PLUGIN(LHCB_2012_I1097092);
103
104}