Rivet analyses

Kinematic distributions in Υ2(1D) → π+π−Υ(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 Υ2(1D) → π+π−Υ(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++ -*-
#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);

}