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Rivet analyses reference
LHCB_2013_I1243156
Helicity angle distributions in excited $D$ meson decays
Experiment: LHCB (LHC)
Inspire ID: 1243156
Status: VALIDATED
Authors:
No references listed
Beams: * *
Beam energies: ANY
Run details:
- Any process producing excited $D$ mesons
The decays $D^{**} \to D^{*+}\pi^-\to D^0\pi^+\pi^-$ 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 $D_1(2420)^0$, $D^*_2(2460)^0$, $D(2650)^0$, $D(2760)$, $D(2580)$, $D(2740)$, $D(3000)$ were measured, but currently only the $D_1(2420)^0$, $D^*_2(2460)^0$ are implemented. The data were read from the plots in the papers and therefore for the $D_1(2420)^0$, $D^*_2(2460)^0$ the error bars are the size of the points in the plots.
Source code:
LHCB_2013_I1243156.cc
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96 | // -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/UnstableParticles.hh"
namespace Rivet {
/// @brief Add a short analysis description here
class LHCB_2013_I1243156 : public Analysis {
public:
/// Constructor
DEFAULT_RIVET_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);
}
/// 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) {
for(const Particle& p : apply<UnstableParticles>(event, "UFS").particles(Cuts::abspid==425 || Cuts::abspid==10423)) {
// 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
_h_D1_ctheta->fill(cTheta);
}
}
/// Normalise histograms etc., after the run
void finalize() {
normalize(_h_D1_ctheta);
normalize(_h_D2_ctheta);
}
//@}
/// @name Histograms
//@{
Histo1DPtr _h_D1_ctheta,_h_D2_ctheta;
//@}
};
// The hook for the plugin system
DECLARE_RIVET_PLUGIN(LHCB_2013_I1243156);
}
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