Rivet analyses

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

namespace Rivet {


  /// @brief J/psi polarization at 7 TeV
  class LHCB_2013_I1244315 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(LHCB_2013_I1244315);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // projections
      declare(Beam(), "Beams");
      declare(UnstableParticles(), "UFS");
      // histograms
      // cross section
      _ybins = {2.0, 2.5, 3.0, 3.5, 4.0, 4.5};
      book(_h_Jpsi, _ybins);
      for (unsigned int iy = 0; iy < 5; ++iy) {
        book(_h_Jpsi->bin(iy + 1), 4, 1, 1 + iy);
        for (unsigned int ix = 0; ix < 2; ++ix) {
          for (unsigned int iz = 0; iz < 3; ++iz) {
            string name = "TMP/POL_" + toString(ix) + "_" + toString(iy) + "_" + toString(iz);
            book(_p_Jpsi[ix][iy][iz], name, refData(1 + ix, 1, 1 + iy));
          }
        }
      }
    }

    void findDecayProducts(const Particle& mother, unsigned int& nstable, Particles& mup, Particles& mum) {
      for (const Particle& p : mother.children()) {
        int id = p.pid();
        if (id == PID::MUON) {
          ++nstable;
          mum.push_back(p);
        }
        else if (id == PID::ANTIMUON) {
          ++nstable;
          mup.push_back(p);
        }
        else if (id == PID::PI0 || id == PID::K0S || id == PID::K0L) {
          ++nstable;
        }
        else if (!p.children().empty()) {
          findDecayProducts(p, nstable, mup, mum);
        }
        else
          ++nstable;
      }
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      // find the beams
      const ParticlePair& beams = apply<Beam>(event, "Beams").beams();
      // Final state of unstable particles to get particle spectra
      const UnstableParticles& ufs = apply<UnstableParticles>(event, "UFS");
      for (const Particle& p : ufs.particles(Cuts::pid == 443)) {
        // prompt
        if (p.fromBottom()) continue;
        // pT and rapidity
        double rapidity = p.rapidity();
        double xp = p.perp();
        // cross section
        _h_Jpsi->fill(rapidity, xp);
        // polarization
        unsigned int nstable = 0;
        Particles mup, mum;
        findDecayProducts(p, nstable, mup, mum);
        if (mup.size() != 1 || mum.size() != 1 || nstable != 2) continue;
        // find the rapidity interval
        if (rapidity <= 2. || rapidity >= 4.5) continue;
        unsigned int iy = 0;
        for (iy = 0; iy < 5; ++iy)
          if (rapidity < _ybins[iy + 1]) break;
        // first the CS frame
        // first boost so upslion momentum =0 in z direction
        Vector3 beta = p.momentum().betaVec();
        beta.setX(0.);
        beta.setY(0.);
        LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(beta);
        FourMomentum pp = boost.transform(p.momentum());
        // and then transverse so pT=0
        beta = pp.betaVec();
        LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(beta);
        // get all the momenta in this frame
        Vector3 muDirn = boost2.transform(boost.transform(mup[0].momentum())).p3().unit();
        FourMomentum p1 = boost2.transform(boost.transform(beams.first.momentum()));
        FourMomentum p2 = boost2.transform(boost.transform(beams.second.momentum()));
        if (beams.first.momentum().z() < 0.) swap(p1, p2);
        if (p.rapidity() < 0.) swap(p1, p2);
        Vector3 axisy = (p1.p3().cross(p2.p3())).unit();
        Vector3 axisz(0., 0., 1.);
        Vector3 axisx = axisy.cross(axisz);
        double cTheta = axisz.dot(muDirn);
        double cPhi = axisx.dot(muDirn);
        // fill the moments
        _p_Jpsi[1][iy][0]->fill(xp, 1.25 * (3. * sqr(cTheta) - 1.));
        _p_Jpsi[1][iy][1]->fill(xp, 1.25 * (1. - sqr(cTheta)) * (2. * sqr(cPhi) - 1.));
        _p_Jpsi[1][iy][2]->fill(xp, 2.5 * cTheta * sqrt(1. - sqr(cTheta)) * cPhi);
        // now for the HX frame
        beta = p.momentum().betaVec();
        boost = LorentzTransform::mkFrameTransformFromBeta(beta);
        axisz = pp.p3().unit();
        axisx = axisy.cross(axisz);
        cTheta = axisz.dot(muDirn);
        cPhi = axisx.dot(muDirn);
        // fill the moments
        _p_Jpsi[0][iy][0]->fill(xp, 1.25 * (3. * sqr(cTheta) - 1.));
        _p_Jpsi[0][iy][1]->fill(xp, 1.25 * (1. - sqr(cTheta)) * (2. * sqr(cPhi) - 1.));
        _p_Jpsi[0][iy][2]->fill(xp, 2.5 * cTheta * sqrt(1. - sqr(cTheta)) * cPhi);
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      double factor = crossSection() / nanobarn / sumOfWeights();
      scale(_h_Jpsi, factor);
      divByGroupWidth(_h_Jpsi);
      for (unsigned int iy = 0; iy < 5; ++iy) {
        // Loop over frame definition
        for (unsigned int iframe = 0; iframe < 2; ++iframe) {
          // book scatters
          Estimate1DPtr lTheta, lPhi, lThetaPhi;
          book(lTheta, iframe + 1, 1, 1 + iy);
          book(lPhi, iframe + 1, 3, 1 + iy);
          book(lThetaPhi, iframe + 1, 2, 1 + iy);
          // histos for the moments
          Profile1DPtr moment[3];
          for (unsigned int ix = 0; ix < 3; ++ix) moment[ix] = _p_Jpsi[iframe][iy][ix];
          // loop over bins
          for (unsigned int ibin = 1; ibin <= moment[0]->bins().size(); ++ibin) {
            // extract moments and errors
            double val[3], err[3];
            // m1 = lTheta/(3+lTheta), m2 = lPhi/(3+lTheta), m3 = lThetaPhi/(3+lTheta)
            for (unsigned int ix = 0; ix < 3; ++ix) {
              val[ix] = moment[ix]->bins()[ibin].numEntries() > 0
                      && moment[ix]->bins()[ibin].effNumEntries() > 0
                  ? moment[ix]->bins()[ibin].mean(2)
                  : 0.;
              err[ix] = moment[ix]->bins()[ibin].numEntries() > 1
                      && moment[ix]->bins()[ibin].effNumEntries() > 1
                  ? moment[ix]->bins()[ibin].stdErr(2)
                  : 0.;
            }
            // values of the lambdas and their errors
            double l1 = 3. * val[0] / (1. - val[0]);
            double e1 = 3. / sqr(1. - val[0]) * err[0];
            double l2 = (3. + l1) * val[1];
            double e2 = 3. / sqr(1. - val[0]) * sqrt(sqr(err[0] * val[1]) + sqr(err[1] * (1. - val[0])));
            double l3 = (3. + l1) * val[2];
            double e3 = 3. / sqr(1. - val[0]) * sqrt(sqr(err[0] * val[1]) + sqr(err[1] * (1. - val[0])));
            // fill the scatters
            lTheta->bin(ibin).setVal(l1);
            lTheta->bin(ibin).setErr(make_pair(e1, e1));
            lPhi->bin(ibin).setVal(l2);
            lPhi->bin(ibin).setErr(make_pair(e2, e2));
            lThetaPhi->bin(ibin).setVal(l3);
            lThetaPhi->bin(ibin).setErr(make_pair(e3, e3));
          }
        }
      }
    }
    /// @}


    /// @name Histograms
    /// @{
    Profile1DPtr _p_Jpsi[2][5][3];
    Histo1DGroupPtr _h_Jpsi;
    vector<double> _ybins;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(LHCB_2013_I1244315);

}