Rivet analyses

ϕ momentum spectra in Υ(4S) decays

Experiment: BABAR (PEP-II)

Inspire ID: 632399

Status: VALIDATED

Authors: - Peter Richardson

References: none listed

Beams: * *

Beam energies: ANY

Run details: - Any process producing Upsilon(4S) originally e+e-

Measurement of the momentum spectrum of ϕ mesons produced in B decays at the Υ(4S) resonance.

Source code:BABAR_2004_I632399.cc

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

namespace Rivet {


  /// @brief phi spectrum at 4S
  class BABAR_2004_I632399 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2004_I632399);


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

    /// Book histograms and initialise projections before the run
    void init() {

      // Initialise and register projections
      declare(UnstableParticles(), "UFS");

      // Book histograms
      book(_b_phi, 1, 1, 1);
      book(_h_phi, 2, 1, 1);
      book(_c_4S, "/TMP/N4S");
    }

    void findDecayProducts(const Particle& p, Particles& phi) {
      for (const Particle& child : p.children()) {
        if (child.pid() == 333)
          phi.push_back(child);
        else if (!child.children().empty())
          findDecayProducts(child, phi);
      }
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      // Find the Upsilons among the unstables
      const UnstableParticles& ufs = apply<UnstableParticles>(event, "UFS");
      Particles upsilons = ufs.particles(Cuts::pid == 300553);
      for (const Particle& ups : upsilons) {
        LorentzTransform cms_boost;
        if (ups.p3().mod() > 1 * MeV)
          cms_boost = LorentzTransform::mkFrameTransformFromBeta(ups.momentum().betaVec());
        Particles phis;
        findDecayProducts(ups, phis);
        _c_4S->fill();

        for (const Particle& phi : phis) {
          FourMomentum p2 = cms_boost.transform(phi.momentum());
          _h_phi->fill(p2.p3().mod());
          _b_phi->fill();
        }
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      if (_c_4S->effNumEntries() != 0) {
        scale(_h_phi, 0.5 / *_c_4S);
        scale(_b_phi, 50. / *_c_4S);
      }
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h_phi;
    CounterPtr _b_phi, _c_4S;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BABAR_2004_I632399);

}