Rivet analyses

title: BABAR_2006_I719949

$e^+e^-\to\rho^0\rho^0$ and $\rho^0\phi^0$ at $\sqrt{s}=10.58\,$GeV

Experiment: BABAR (PEP-II)

Inspire ID: 719949

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.Lett. 97 (2006) 112002

Beams: e+ e-

Beam energies: (5.3, 5.3)GeV

Run details: - e+ e- > hadrons

Measurement of the cross section, production angle and helicity angles in the decays for $e^+e^-\to\rho^0\rho^0$ and $\rho^0\phi^0$ at $\sqrt{s}=10.58\,$GeV. The cross section was taken from the tet of the paper and the corrected angular distributionss from figures 5 and 6.

Source code:BABAR_2006_I719949.cc

```c++ // -- C++ --

include "Rivet/Analysis.hh"

include "Rivet/Projections/Beam.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief e+e -> rho 0 rho and rho0 phi class BABAR_2006_I719949 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2006_I719949);


/// @name Analysis methods
/// @{

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  declare(Beam(), "Beams");
  declare(UnstableParticles(Cuts::pid == 113 or Cuts::pid == 333), "UFS");
  declare(FinalState(), "FS");
  // histos
  for (unsigned int ix = 0; ix < 3; ++ix) {
    book(_h_hel[ix], 3, 1, 1 + ix);
    if (ix == 2) continue;
    book(_h_sigma[ix], 1, 1, 1 + ix);
    book(_h_prod[ix], 2, 1, 1 + ix);
  }
}

void findChildren(const Particle& p, map<long, int>& nRes, int& ncount) {
  for (const Particle& child : p.children()) {
    if (child.children().empty()) {
      nRes[child.pid()] -= 1;
      --ncount;
    }
    else
      findChildren(child, nRes, ncount);
  }
}

/// Perform the per-event analysis
void analyze(const Event& event) {
  // get the axis, direction of incoming electron
  const ParticlePair& beams = apply<Beam>(event, "Beams").beams();
  Vector3 axis;
  if (beams.first.pid() > 0)
    axis = beams.first.momentum().p3().unit();
  else
    axis = beams.second.momentum().p3().unit();
  // types of final state particles
  const FinalState& fs = apply<FinalState>(event, "FS");
  map<long, int> nCount;
  int ntotal(0);
  for (const Particle& p : fs.particles()) {
    nCount[p.pid()] += 1;
    ++ntotal;
  }
  // loop over rho mesons
  const Particles vMesons = apply<UnstableParticles>(event, "UFS").particles();
  Particle vectors[2];
  bool matched(false);
  for (unsigned int ix = 0; ix < vMesons.size(); ++ix) {
    if (vMesons[ix].children().empty()) continue;
    map<long, int> nRes = nCount;
    int ncount = ntotal;
    findChildren(vMesons[ix], nRes, ncount);
    matched = false;
    for (unsigned int iy = ix + 1; iy < vMesons.size(); ++iy) {
      if (vMesons[iy].children().empty()) continue;
      if (vMesons[ix].pid() == 333 && vMesons[iy].pid() == 333) continue;
      map<long, int> nRes2 = nRes;
      int ncount2 = ncount;
      findChildren(vMesons[iy], nRes2, ncount2);
      if (ncount2 == 0) {
        matched = true;
        for (const auto& val : nRes2) {
          if (val.second != 0) {
            matched = false;
            break;
          }
        }
        if (matched) {
          vectors[0] = vMesons[ix];
          vectors[1] = vMesons[iy];
          break;
        }
      }
    }
    if (matched) break;
  }
  if (!matched) vetoEvent;
  if (vectors[0].pid() == 333) swap(vectors[0], vectors[1]);
  if (vectors[0].children().size() != 2) vetoEvent;
  if (vectors[1].children().size() != 2) vetoEvent;
  double cTheta = abs(axis.dot(vectors[0].momentum().p3().unit()));
  if (cTheta > 0.8) vetoEvent;
  if (vectors[0].pid() == vectors[1].pid()) {
    _h_sigma[0]->fill("10.58"s);
    _h_prod[0]->fill(cTheta);
  }
  else {
    _h_sigma[1]->fill("10.58"s);
    _h_prod[1]->fill(cTheta);
  }
  // helicity angles
  double cHel[2];
  for (unsigned int ix = 0; ix < 2; ++ix) {
    int iMeson = vectors[ix].pid() == 113 ? 211 : 321;
    Particle mP;
    if (vectors[ix].children()[0].pid() == iMeson && vectors[ix].children()[1].pid() == -iMeson)
      mP = vectors[ix].children()[0];
    else if (vectors[ix].children()[1].pid() == iMeson && vectors[ix].children()[0].pid() == -iMeson)
      mP = vectors[ix].children()[1];
    else
      vetoEvent;
    // boost to the rho+ rest frame
    LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(
        vectors[ix].momentum().betaVec());
    Vector3 e1z = vectors[ix].momentum().p3().unit();
    Vector3 axis1 = boost1.transform(mP.momentum()).p3().unit();
    cHel[ix] = e1z.dot(axis1);
  }
  if (vectors[0].pid() == vectors[1].pid()) {
    _h_hel[0]->fill(cHel[0]);
    _h_hel[0]->fill(cHel[1]);
  }
  else {
    _h_hel[1]->fill(cHel[1]);
    _h_hel[2]->fill(cHel[0]);
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  double fact = crossSection() / sumOfWeights() / femtobarn;
  for (unsigned int ix = 0; ix < 3; ++ix) {
    normalize(_h_hel[ix], 1., false);
    if (ix == 2) continue;
    scale(_h_sigma[ix], fact);
    normalize(_h_prod[ix], 1., false);
  }
}

/// @}


/// @name Histograms
/// @{
BinnedHistoPtr<string> _h_sigma[2];
Histo1DPtr _h_prod[2], _h_hel[3];
/// @}

};

RIVET_DECLARE_PLUGIN(BABAR_2006_I719949);

} ```