Rivet analyses

Electron spectrum inclusive semi-leptonic in B decays

Experiment: BABAR (PEP-II)

Inspire ID: 1498564

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev. D95 (2017) no.7, 072001

Beams: * *

Beam energies: ANY

Run details: - bottom mesons produced at the Upsilon(4S)

Measurement of the electron spectrum inclusive semi-leptonic in B decays, including both the total and the charmless. N.B. The spectum is obtained in the rest frame of the decaying Υ(4S) which produces the decaying B mesons

Source code:BABAR_2017_I1498564.cc

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

namespace Rivet {


  /// @brief Electron spectrum in B decays
  class BABAR_2017_I1498564 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2017_I1498564);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // projections
      declare(UnstableParticles(Cuts::pid == 300553), "UFS");
      // Book histograms
      // specify custom binning
      book(_h_light, 1, 1, 1);
      book(_h_all, 1, 1, 2);
      book(_nB, "/TMP/nB");
    }


    void findDecayProducts(Particle parent,
                           Particles& em,
                           Particles& ep,
                           Particles& nue,
                           Particles& nueBar,
                           bool& charm) {
      for (const Particle& p : parent.children()) {
        if (PID::isCharmHadron(p.pid())) {
          charm = true;
        }
        else if (p.pid() == PID::EMINUS) {
          em.push_back(p);
        }
        else if (p.pid() == PID::EPLUS) {
          ep.push_back(p);
        }
        else if (p.pid() == PID::NU_E) {
          nue.push_back(p);
        }
        else if (p.pid() == PID::NU_EBAR) {
          nueBar.push_back(p);
        }
        else if (PID::isBottomHadron(p.pid())) {
          findDecayProducts(p, em, ep, nue, nueBar, charm);
        }
        else if (!PID::isHadron(p.pid())) {
          findDecayProducts(p, em, ep, nue, nueBar, charm);
        }
      }
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      // find and loop over Upslion(4S)
      for (const Particle& p : apply<UnstableParticles>(event, "UFS").particles()) {
        // boost to rest frame
        LorentzTransform cms_boost;
        if (p.p3().mod() > 1 * MeV)
          cms_boost = LorentzTransform::mkFrameTransformFromBeta(p.momentum().betaVec());
        // loop over decay products
        for (const Particle& p2 : p.children()) {
          if (p2.abspid() == 511 || p2.abspid() == 521) {
            _nB->fill();
            bool charm = false;
            Particles em, ep, nue, nueBar;
            findDecayProducts(p2, em, ep, nue, nueBar, charm);
            if (em.size() == 1 && nueBar.size() == 1) {
              double pmod = cms_boost.transform(em[0].momentum()).p3().mod();
              _h_all->fill(pmod);
              if (!charm) _h_light->fill(pmod);
            }
            else if (ep.size() == 1 && nue.size() == 1) {
              double pmod = cms_boost.transform(ep[0].momentum()).p3().mod();
              _h_all->fill(pmod);
              if (!charm) _h_light->fill(pmod);
            }
          }
        }
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {

      // normalize to number of B decays
      scale(_h_all, 1. / *_nB);
      scale(_h_light, 1. / *_nB);
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h_light, _h_all;
    CounterPtr _nB;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BABAR_2017_I1498564);

}