Rivet analyses

Longitudinal polarization in B± → ϕK1± and ϕK2±

Experiment: BABAR (PEP-II)

Inspire ID: 789278

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.Lett. 101 (2008) 161801

Beams: * *

Beam energies: ANY

Run details: - Any process producing B+ mesons, originally Upsilon(4S) decays

Measurement of the longitudinal polarization in B± → ϕK1± and ϕK2±. The values were taken from Table I, due to the large backgrounds none of the distributions are implemented.

Source code:BABAR_2008_I789278.cc

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

namespace Rivet {


  /// @brief B+ -> K_1+/K_2+ phixs
  class BABAR_2008_I789278 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2008_I789278);


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

    /// Book histograms and initialise projections before the run
    void init() {
      UnstableParticles ufs = UnstableParticles(Cuts::abspid == 521);
      declare(ufs, "UFS");
      DecayedParticles BP(ufs);
      BP.addStable(10323);
      BP.addStable(-10323);
      BP.addStable(325);
      BP.addStable(-325);
      BP.addStable(333);
      declare(BP, "BP");
      // histos
      for (unsigned int ix = 0; ix < 2; ++ix) {
        book(_p[ix][0], 1, 1, 1 + ix);
        book(_p[ix][1], "TMP/wgt_" + toString(ix + 1));
      }
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      static const map<PdgId, unsigned int>& mode1 = {{333, 1}, {10323, 1}};
      static const map<PdgId, unsigned int>& mode1CC = {{333, 1}, {-10323, 1}};
      static const map<PdgId, unsigned int>& mode2 = {{333, 1}, {325, 1}};
      static const map<PdgId, unsigned int>& mode2CC = {{333, 1}, {-325, 1}};

      DecayedParticles BP = apply<DecayedParticles>(event, "BP");
      // loop over particles
      for (unsigned int ix = 0; ix < BP.decaying().size(); ++ix) {
        int imode = -1;
        if (BP.modeMatches(ix, 2, mode1) || BP.modeMatches(ix, 2, mode1CC))
          imode = 0;
        else if (BP.modeMatches(ix, 2, mode2) || BP.modeMatches(ix, 2, mode2CC))
          imode = 1;
        else
          continue;
        // find phi decay products
        const Particle& phi = BP.decayProducts()[ix].at(333)[0];
        if (phi.children().size() != 2) continue;
        if (phi.children()[0].pid() != -phi.children()[1].pid()) continue;
        if (phi.children()[0].abspid() != 321) continue;
        Particle Kp = phi.children()[0].pid() > 0 ? phi.children()[0] : phi.children()[1];
        // boost to B rest frame
        LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(
            BP.decaying()[ix].momentum().betaVec());
        FourMomentum pPhi = boost.transform(phi.momentum());
        FourMomentum pKp = boost.transform(Kp.momentum());
        const LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pPhi.betaVec());
        pKp = boost2.transform(pKp);
        double cK = pKp.p3().unit().dot(pPhi.p3().unit());
        _p[imode][0]->fill(-(1. - 5. * sqr(cK)) / 2.);
        _p[imode][1]->fill();
      }
    }


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

    /// @}


    /// @name Histograms
    /// @{
    CounterPtr _p[2][2];
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BABAR_2008_I789278);

}