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| // -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/UnstableParticles.hh"
namespace Rivet {
/// @brief tau polarization in B -> D* tau nu_tau
class BELLE_2018_I1621272 : public Analysis {
public:
/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2018_I1621272);
/// @name Analysis methods
///@{
/// Book histograms and initialise projections before the run
void init() {
// Initialise and register projections
declare(UnstableParticles(), "UFS");
// Book histograms
book(_h_pi ,"/TMP/PI" ,20,-1.,1.);
book(_h_rho,"/TMP/RHO",20,-1.,1.);
}
void findChildren(const Particle & p, int & sign, unsigned int & nprod,
Particles & Dstar, Particles & tau, Particles & nu) {
for(const Particle & child : p.children()) {
if(child.pid()==-sign*413 || child.pid()==-sign*423) {
++nprod;
Dstar.push_back(child);
}
else if(child.pid()==-sign*15) {
++nprod;
tau.push_back(child);
}
else if(child.pid()==sign*16) {
++nprod;
nu.push_back(child);
}
else if(child.pid()==22)
continue;
else if(child.children().empty() ||
child.pid()==111 || child.pid()==221 || child.pid()==331) {
++nprod;
}
else {
findChildren(child,sign,nprod,Dstar,tau,nu);
}
}
}
void findTau(const Particle & p, int & sign, unsigned int & nprod,
Particles & piP, Particles & pi0, Particles & nu) {
for(const Particle & child : p.children()) {
if(child.pid()==111) {
++nprod;
pi0.push_back(child);
}
else if(child.pid()==sign*211) {
++nprod;
piP.push_back(child);
}
else if(child.pid()==-sign*16) {
++nprod;
nu.push_back(child);
}
else if(child.pid()==22)
continue;
else if(child.children().empty() || child.pid()==221 || child.pid()==331) {
++nprod;
}
else {
findTau(child,sign,nprod,piP,pi0,nu);
}
}
}
/// Perform the per-event analysis
void analyze(const Event& event) {
// Loop over B0 mesons
for(const Particle& p : apply<UnstableParticles>(event, "UFS").particles(Cuts::abspid==PID::B0 or
Cuts::abspid==PID::BPLUS)) {
// find the B decay
int sign = p.pid()/p.abspid();
unsigned int nprod = 0;
Particles Dstar,tau,nu;
findChildren(p,sign,nprod,Dstar,tau,nu);
if(nprod!=3 || Dstar.size()!=1 || tau.size() !=1 || nu.size()!=1)
continue;
// check decay
if(p.pid()==PID::B0) {
if(Dstar[0].pid()!=-sign*413) vetoEvent;
}
else if(p.pid()==PID::BPLUS) {
if(Dstar[0].pid()!=-sign*423) vetoEvent;
}
// find the tau decay
nprod=0;
nu.clear();
Particles piP,pi0;
findTau(tau[0],sign,nprod,piP,pi0,nu);
if(nu.size()!=1) continue;
LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(p.momentum().betaVec());
FourMomentum ptau = boost1.transform(tau[0].momentum());
LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(ptau);
// pion mode
if(nprod==2 && piP.size()==1) {
FourMomentum pPi = boost2.transform(boost1.transform(piP[0].momentum()));
double cTheta = pPi.p3().unit().dot(ptau.p3().unit());
_h_pi->fill(cTheta);
}
// rho mode
else if(nprod==3 && piP.size()==1 && pi0.size()==1) {
FourMomentum pRho = boost2.transform(boost1.transform(piP[0].momentum()+pi0[0].momentum()));
double cTheta = pRho.p3().unit().dot(ptau.p3().unit());
_h_rho->fill(cTheta);
}
}
}
pair<double,double> calcAlpha(Histo1DPtr hist) {
if(hist->numEntries()==0.) return make_pair(0.,0.);
double sum1(0.),sum2(0.);
for (auto bin : hist->bins() ) {
double Oi = bin.area();
if(Oi==0.) continue;
double ai = 0.5*(bin.xMax()-bin.xMin());
double bi = 0.5*ai*(bin.xMax()+bin.xMin());
double Ei = bin.areaErr();
sum1 += sqr(bi/Ei);
sum2 += bi/sqr(Ei)*(Oi-ai);
}
return make_pair(sum2/sum1,sqrt(1./sum1));
}
/// Normalise histograms etc., after the run
void finalize() {
normalize(_h_pi );
normalize(_h_rho);
// the polarization
Scatter2DPtr _h_alpha;
book(_h_alpha,1,1,2);
pair<double,double> alpha_pi = calcAlpha(_h_pi );
pair<double,double> alpha_rho = calcAlpha(_h_rho);
// 0.45 factor for rho
alpha_rho.first /=0.46;
alpha_rho.second/=0.46;
pair<double,double> alpha;
alpha.first = (alpha_pi.first*sqr(alpha_rho.second)+alpha_rho.first*sqr(alpha_pi.second))/(sqr(alpha_pi.second)+sqr(alpha_rho.second));
alpha.second = alpha_pi.second*alpha_rho.second/sqrt(sqr(alpha_pi.second)+sqr(alpha_rho.second));
_h_alpha->addPoint(0.5,alpha.first, make_pair(0.5,0.5), make_pair(alpha.second,alpha.second) );
}
///@}
/// @name Histograms
///@{
Histo1DPtr _h_pi,_h_rho;
///@}
};
RIVET_DECLARE_PLUGIN(BELLE_2018_I1621272);
}
|