Rivet analyses
Helicity angle distributions in excited D meson decays
Experiment: LHCB (LHC)
Inspire ID: 1243156
Status: VALIDATED
Authors: - Peter Richardson
References: none listed
Beams: * *
Beam energies: ANY
Run details: - Any process producing excited D mesons
The decays D** → D*+π− → D0π+π− are used to measure the helicity angle, i.e. the angle between the two pions in the rest frame of the D*. The decays of D1(2420)0, D2*(2460)0, D(2650)0, D(2760), D(2580), D(2740), D(3000) were measured,currently the D(3000)0 is not implemented. The data were read from the plots in the papers and therefore for the D1(2420)0, D2*(2460)0 the error bars are the size of the points in the plots.
Source
code:LHCB_2013_I1243156.cc
// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/UnstableParticles.hh"
namespace Rivet {
/// @brief Helicity angle distributions in excited $D$ meson decays
class LHCB_2013_I1243156 : public Analysis {
public:
/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(LHCB_2013_I1243156);
/// @name Analysis methods
/// @{
/// Book histograms and initialise projections before the run
void init() {
// Initialise and register projections
declare(UnstableParticles(), "UFS");
// Book histograms
book(_h_D1_ctheta , 8,1,1);
book(_h_D2_ctheta , 8,1,2);
book(_h_DStar2S_ctheta, 9,1,1);
book(_h_D3_ctheta , 9,1,2);
book(_h_D2S_ctheta ,10,1,1);
book(_h_D21D_ctheta ,10,1,2);
}
/// Recursively walk the decay tree to find decay products of @a p
void findDecayProducts(Particle mother, Particles & dstar, Particles & d0, Particles & pi,unsigned int & ncount) {
for(const Particle & p: mother.children()) {
if(p.abspid()==413)
dstar.push_back(p);
else if(p.abspid()==421)
d0.push_back(p);
else if(p.abspid()==211)
pi.push_back(p);
ncount +=1;
}
}
/// Perform the per-event analysis
void analyze(const Event& event) {
const Particles usps = apply<UnstableParticles>(event, "UFS")
.particles(Cuts::abspid==425 || Cuts::abspid==10423 || Cuts::abspid==100423 || Cuts::abspid==427||
Cuts::abspid==100421 || Cuts::abspid==10425 || Cuts::abspid==20425);
for (const Particle& p : usps) {
// decay products
Particles dstar,d0,pi;
unsigned int ncount=0;
findDecayProducts(p,dstar,d0, pi,ncount);
if (ncount!=2 || dstar.size()!=1 || pi.size()!=1 || d0.size()!=0 ) continue;
if (dstar[0].pid()/p.pid()<0) continue;
Particle p2 = dstar[0];
LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(p2.momentum().betaVec());
Vector3 d1 = boost.transform(pi[0].momentum()).p3().unit();
ncount=0;
dstar.clear();
d0.clear();
pi.clear();
findDecayProducts(p2,dstar,d0, pi,ncount);
if (ncount!=2 || dstar.size()!=0 || pi.size()!=1 || d0.size()!=1 ) continue;
if (pi[0].pid()/p2.pid()<0) continue;
Vector3 d2 = boost.transform(pi[0].momentum()).p3().unit();
double cTheta = d1.dot(d2);
// decay angles
if (p.abspid()==425)
_h_D2_ctheta->fill(cTheta);
else if (p.abspid()==10423)
_h_D1_ctheta->fill(cTheta);
else if (p.abspid()==100423)
_h_DStar2S_ctheta->fill(cTheta);
else if (p.abspid()==427)
_h_D3_ctheta->fill(cTheta);
else if (p.abspid()==100421)
_h_D2S_ctheta->fill(cTheta);
else if (p.abspid()==10425 || p.abspid()==20425)
_h_D21D_ctheta->fill(cTheta);
}
}
/// Normalise histograms etc., after the run
void finalize() {
normalize(_h_D1_ctheta);
normalize(_h_D2_ctheta);
normalize(_h_DStar2S_ctheta);
normalize(_h_D3_ctheta );
normalize(_h_D2S_ctheta );
normalize(_h_D21D_ctheta );
}
/// @}
/// @name Histograms
/// @{
Histo1DPtr _h_D1_ctheta,_h_D2_ctheta;
Histo1DPtr _h_DStar2S_ctheta,_h_D3_ctheta;
Histo1DPtr _h_D2S_ctheta,_h_D21D_ctheta;
/// @}
};
RIVET_DECLARE_PLUGIN(LHCB_2013_I1243156);
}