Rivet analyses

title: BABAR_2010_I850492

Kinematic distributions in $\Upsilon_2(1D)\to\pi^+\pi^-\Upsilon(1S)$

Experiment: BABAR (PEP-II)

Inspire ID: 850492

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 82 (2010) 111102

Beams: * *

Beam energies: ANY

Run details: - Any process producing Upsilon_2(1D)

Measurement of the kinematic distributions in $\Upsilon_2(1D)\to\pi^+\pi^-\Upsilon(1S)$ by BABAR. The data were read from the paper and may not have been corrected for acceptance.

Source code:BABAR_2010_I850492.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief Upsilon_2 -> pi+ pi- Upsilon class BABAR_2010_I850492 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2010_I850492);


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

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  UnstableParticles ufs = UnstableParticles(Cuts::pid == 20555);
  declare(ufs, "UFS");
  DecayedParticles Upsilon2(ufs);
  Upsilon2.addStable(PID::PI0);
  Upsilon2.addStable(553);
  declare(Upsilon2, "Upsilon2");
  for (unsigned int ix = 0; ix < 3; ++ix) book(_h[ix], 1, 1, 1 + ix);
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  static const map<PdgId, unsigned int>& mode = {{211, 1}, {-211, 1}, {553, 1}};
  DecayedParticles Upsilon2 = apply<DecayedParticles>(event, "Upsilon2");
  // loop over particles
  for (unsigned int ix = 0; ix < Upsilon2.decaying().size(); ++ix) {
    if (!Upsilon2.modeMatches(ix, 3, mode)) continue;
    const Particle& pip = Upsilon2.decayProducts()[ix].at(211)[0];
    const Particle& pim = Upsilon2.decayProducts()[ix].at(-211)[0];
    const Particle& ups = Upsilon2.decayProducts()[ix].at(553)[0];
    FourMomentum ptot = pip.momentum() + pim.momentum();
    _h[0]->fill(ptot.mass());
    // boost to Upsilon_2 rest frame
    LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(
        Upsilon2.decaying()[ix].momentum().betaVec());
    FourMomentum pDir = boost.transform(ptot);
    Matrix3 ptoz(-pDir.p3().unit(), Vector3(0, 0, 1));
    boost.preMult(ptoz);
    FourMomentum p2 = boost.transform(ups.momentum());
    FourMomentum ppip = boost.transform(pip.momentum());
    FourMomentum ppim = boost.transform(pim.momentum());
    ptot = ppip + ppim;
    // pion angle
    LorentzTransform boostPi = LorentzTransform::mkFrameTransformFromBeta(ptot.betaVec());
    Vector3 axisPi = boostPi.transform(ppip).p3().unit();
    double cosPi = axisPi.dot(ptot.p3().unit());
    _h[2]->fill(abs(cosPi));
    if (ups.children().size() != 2) continue;
    Particle ep, em;
    if (ups.children()[0].pid() == -ups.children()[1].pid()
        && (ups.children()[0].abspid() == 11 || ups.children()[0].abspid() == 13)) {
      ep = ups.children()[0];
      em = ups.children()[1];
    }
    else
      continue;
    if (em.pid() < 0) swap(ep, em);
    LorentzTransform boostUps = LorentzTransform::mkFrameTransformFromBeta(p2.betaVec());
    FourMomentum pe = boost.transform(ep.momentum());
    Vector3 axisE = boostUps.transform(pe).p3().unit();
    axisPi.setZ(0.);
    axisE.setZ(0.);
    double chi = abs(atan2(axisE.cross(axisPi).dot(p2.p3().unit()), axisE.dot(axisPi)));
    if (chi > M_PI) chi = 2. * M_PI - chi;
    _h[1]->fill(chi);
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  for (unsigned int ix = 0; ix < 3; ++ix) normalize(_h[ix], 1., false);
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h[3];
/// @}

};

RIVET_DECLARE_PLUGIN(BABAR_2010_I850492);

} ```