// $Id: helicityAngle.cc,v 1.14 2007/12/11 08:42:53 hegner Exp $
#include "CommonTools/CandUtils/interface/helicityAngle.h"
#include "DataFormats/Candidate/interface/Candidate.h"
#include "CommonTools/CandUtils/interface/Booster.h"
#include <Math/VectorUtil.h>
using namespace reco;
using namespace std;

double helicityAngle(const reco::Candidate& mother, const reco::Candidate& daughter) {
  Particle::Vector boost = mother.p4().BoostToCM();
  Particle::LorentzVector pdau = ROOT::Math::VectorUtil::boost(daughter.p4(), boost);
  double h = ROOT::Math::VectorUtil::Angle(pdau, boost);
  if (h > M_PI / 2)
    h = M_PI - h;
  return h;
}

double helicityAngle(const Candidate& cand) {
  assert(cand.numberOfDaughters() == 2);
  return helicityAngle(cand, *cand.daughter(0));
}