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BABAR_2009_I827985

Helicity angle distributions in excited $D_s$ meson decays
Experiment: BABAR (PEP-II)
Inspire ID: 827985
Status: VALIDATED
Authors:
  • Peter Richardson
References:
  • Phys.Rev.D 80 (2009) 092003
Beams: * *
Beam energies: ANY
Run details:
  • Any process producing excited $D_s$ mesons

The decays $D_s^{**} \to D^{*+}K^0_S\to D^0\pi^+K^0_S$ are used to measure the helicity angle, i.e. the angle between the pion and kaon in the rest frame of the $D^*$. The decays of $D_{s1}^*(2700)^+$ and with mass 2.8 GeV were measured. It is unclear if this is the $D_{s1}^*(2860)^+$, $D_{s3}^*(2860)^+$ or a mixture of the two. This histogram is therefore filled we with each state and the admixture. The data were read from the plots in the papers.

Source code: BABAR_2009_I827985.cc
  1// -*- C++ -*-
  2#include "Rivet/Analysis.hh"
  3#include "Rivet/Projections/UnstableParticles.hh"
  4
  5namespace Rivet {
  6
  7
  8  /// @brief D**_s decays
  9  class BABAR_2009_I827985 : public Analysis {
 10  public:
 11
 12    /// Constructor
 13    RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2009_I827985);
 14
 15
 16    /// @name Analysis methods
 17    /// @{
 18
 19    /// Book histograms and initialise projections before the run
 20    void init() {
 21
 22      // Initialise and register projections
 23      declare(UnstableParticles(), "UFS");
 24
 25      // Book histograms
 26      book(_h_DStar_ctheta, 1,1,1);
 27      book(_h_D3_ctheta[0], 1,1,2);
 28      book(_h_D3_ctheta[1], 1,1,3);
 29      book(_h_D3_ctheta[2], 1,1,4);
 30    }
 31
 32    /// Recursively walk the decay tree to find decay products of @a p
 33    void findDecayProducts(Particle mother, Particles & dstar, Particles & d0, Particles & K0, Particles & pi, unsigned int & ncount) {
 34      for(const Particle & p: mother.children()) {
 35	if(p.abspid()==413)
 36	  dstar.push_back(p);
 37	else if(p.abspid()==421)
 38	  d0.push_back(p);
 39	else if(p.abspid()==130 || p.abspid()==130 || p.abspid()==311)
 40	  K0.push_back(p);
 41	else if(p.abspid()==211)
 42	  pi.push_back(p);
 43	ncount +=1;
 44      }
 45    }
 46
 47    /// Perform the per-event analysis
 48    void analyze(const Event& event) {
 49      for(const Particle& p : apply<UnstableParticles>(event, "UFS").particles(Cuts::abspid==100433 || Cuts::abspid==437 ||
 50									       Cuts::abspid==30433)) {
 51	// decay products
 52	Particles dstar,d0,K0,pi;
 53	unsigned int ncount=0;
 54	findDecayProducts(p, dstar, d0, K0, pi, ncount);
 55	if(ncount!=2 || dstar.size()!=1 || K0.size()!=1 ) continue;
 56	if(dstar[0].pid()/p.pid()<0) continue;
 57	Particle p2 = dstar[0];
 58	LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(p2.momentum().betaVec());
 59	Vector3 d1 = boost.transform(K0[0].momentum()).p3().unit();
 60	ncount=0;
 61	dstar.clear();
 62	d0.clear();
 63	pi.clear();
 64	findDecayProducts(p2, dstar, d0, K0, pi, ncount);
 65	if(ncount!=2 || pi.size()!=1 || d0.size()!=1 ) continue;
 66	if(pi[0].pid()/p2.pid()<0) continue;
 67	Vector3 d2 = boost.transform(pi[0].momentum()).p3().unit();
 68	double cTheta  = d1.dot(d2);
 69	// decay angles
 70	if(p.abspid()==100433)
 71	  _h_DStar_ctheta->fill(cTheta);
 72	else if(p.abspid()==30433) {
 73	  _h_D3_ctheta[0]->fill(cTheta);
 74	  _h_D3_ctheta[2]->fill(cTheta);
 75	}
 76	else if(p.abspid()==437) {
 77	  _h_D3_ctheta[1]->fill(cTheta);
 78	  _h_D3_ctheta[2]->fill(cTheta);
 79	}
 80      }
 81    }
 82
 83
 84    /// Normalise histograms etc., after the run
 85    void finalize() {
 86      normalize(_h_DStar_ctheta);
 87      normalize(_h_D3_ctheta[0]);
 88      normalize(_h_D3_ctheta[1]);
 89      normalize(_h_D3_ctheta[2]);
 90    }
 91
 92    /// @}
 93
 94
 95    /// @name Histograms
 96    /// @{
 97    Histo1DPtr _h_DStar_ctheta,_h_D3_ctheta[3];
 98    /// @}
 99
100
101  };
102
103
104  RIVET_DECLARE_PLUGIN(BABAR_2009_I827985);
105
106}