Rivet analyses

Mass and angular distributions in BS0 → Jψπ+π−

Experiment: BELLE (KEKB)

Inspire ID: 889524

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.Lett. 106 (2011) 121802

Beams: * *

Beam energies: ANY

Run details: - Any process producing B_s0, original Upsilon(5S) decay

THe π+π− mass distribution and helcity angle distributions in the f0(980) and f0(1370) mass regions for the decay BS0 → Jψπ+π− measured by BELLE

Source code:BELLE_2011_I889524.cc

// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/DecayedParticles.hh"
#include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {


  /// @brief Bs0 -> pi+ pi- J/psi
  class BELLE_2011_I889524 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2011_I889524);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // projections
      UnstableParticles ufs = UnstableParticles(Cuts::abspid == 531);
      declare(ufs, "UFS");
      DecayedParticles BS0(ufs);
      BS0.addStable(443);
      declare(BS0, "BS0");
      // histograms
      book(_h_mass, 1, 1, 1);
      for (unsigned int ix = 0; ix < 2; ++ix) book(_h_cTheta[ix], 2, 1, 1 + ix);
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      static const map<PdgId, unsigned int>& mode = {{211, 1}, {-211, 1}, {443, 1}};
      DecayedParticles BS0 = apply<DecayedParticles>(event, "BS0");
      for (unsigned int ix = 0; ix < BS0.decaying().size(); ++ix) {
        if (!BS0.modeMatches(ix, 3, mode)) continue;
        const Particle& pip = BS0.decayProducts()[ix].at(211)[0];
        const Particle& pim = BS0.decayProducts()[ix].at(-211)[0];
        const Particle& JPsi = BS0.decayProducts()[ix].at(443)[0];
        double mpipi = (pip.momentum() + pim.momentum()).mass();
        _h_mass->fill(mpipi);
        // helicity angle find J.psi leptonic children
        if (JPsi.children().size() != 2) continue;
        if (JPsi.children()[0].pid() != -JPsi.children()[1].pid()) continue;
        if (JPsi.children()[0].abspid() != PID::EMINUS && JPsi.children()[0].abspid() != PID::MUON) continue;
        Particle lm = JPsi.children()[0];
        Particle lp = JPsi.children()[1];
        if (lm.pid() < 0) swap(lm, lp);
        LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(
            BS0.decaying()[ix].momentum().betaVec());
        FourMomentum ppsi = boost1.transform(JPsi.momentum());
        Vector3 axis1 = ppsi.p3().unit();
        LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(ppsi.betaVec());
        FourMomentum plp = boost2.transform(boost1.transform(lp.momentum()));
        double cTheta = plp.p3().unit().dot(axis1);
        if (mpipi > 0.8 && mpipi < 1.16)
          _h_cTheta[0]->fill(cTheta);
        else if (mpipi > 1.3 && mpipi < 1.5)
          _h_cTheta[1]->fill(cTheta);
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      normalize(_h_mass, 1., false);
      for (unsigned int ix = 0; ix < 2; ++ix) normalize(_h_cTheta[ix], 1., false);
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h_mass, _h_cTheta[2];
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BELLE_2011_I889524);

}