Rivet analyses

CP asymmetry in B̄ → Xs + Dγ decays

Experiment: BABAR (PEP-II)

Inspire ID: 1337783

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.Lett. 114 (2015) 15, 151601

Beams: * *

Beam energies: ANY

Run details: - B− and B̄0 mesons in Upsilon(4S) decays (needed as photon energy measured in Upsilon(4S) rest frame)

Measurement of the CP asymmetry in B̄ → Xs + Dγ decays

Source code:BABAR_2015_I1337783.cc

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

namespace Rivet {


  /// @brief CP asymetry in B -> X gamma
  class BABAR_2015_I1337783 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2015_I1337783);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      declare(UnstableParticles(Cuts::pid == 300553), "UFS");
      // profile hist for asymmetry
      book(_p, 1, 1, 1);
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      if (_edges.empty()) _edges = _p->xEdges();
      // 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 children
        for (const Particle& p2 : p.children(Cuts::abspid == 521 || Cuts::abspid == 511)) {
          Particle bottom = p2;
          while (bottom.children()[0].abspid() == p2.abspid()) bottom = bottom.children()[0];
          bool charm = false;
          FourMomentum pgamma(0., 0., 0., 0.);
          unsigned int ngamma = 0;
          for (const Particle& child : bottom.children()) {
            if (child.pid() == PID::PHOTON) {
              ngamma += 1;
              pgamma += child.momentum();
            }
            else if (PID::isCharmHadron(child.pid()))
              charm = true;
          }
          if (ngamma != 1 || charm) continue;
          double Egamma = cms_boost.transform(pgamma).E();
          double wgt = bottom.pid() < 0 ? 100. : -100.;
          double Emin = 1.7;
          for (unsigned int ix = 0; ix < _edges.size(); ++ix) {
            if (Egamma > Emin) _p->fill(_edges[ix], wgt);
            Emin += 0.1;
          }
        }
      }
    }


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

    /// @}


    /// @name Histograms
    /// @{
    BinnedProfilePtr<string> _p;
    vector<string> _edges;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BABAR_2015_I1337783);

}