Rivet analyses

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

namespace Rivet {


  /// @brief OPAL K*0 fragmentation function paper
  ///
  /// @author Peter Richardson
  class OPAL_1997_I447146 : public Analysis {
  public:

    RIVET_DEFAULT_ANALYSIS_CTOR(OPAL_1997_I447146);


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

    void init() {
      declare(Beam(), "Beams");
      declare(ChargedFinalState(), "FS");
      declare(UnstableParticles(), "UFS");
      book(_histXeK0, 1, 1, 1);
      const vector<double> edges{0., 0.01, 0.03, 0.1, 0.125, 0.14, 0.16, 0.2, 0.3, 0.4, 0.5, 0.7, 1.0};
      book(_h_ctheta, edges);
      book(_h_alpha, edges);
      for (size_t ix = 0; ix < _h_ctheta->numBins(); ++ix) {
        string suff = to_string(ix);
        if (suff.length() == 1) suff = "0" + suff;
        book(_h_ctheta->bin(ix + 1), "ctheta_" + suff, 20, -1.0, 1.0);
        book(_h_alpha->bin(ix + 1), "alpha_" + suff, 20, 0.0, 0.5 * M_PI);
      }
      book(_h_ctheta_large, "ctheta_large", 20, -1.0, 1.0);


      book(_h_alpha_low, {0.3, 0.4, 0.5, 0.7, 1.0});
      book(_h_alpha_high, {0.3, 0.4, 0.5, 0.7, 1.0});
      for (size_t ix = 0; ix < _h_alpha_low->numBins(); ++ix) {
        string suff = std::to_string(ix);
        book(_h_alpha_low->bin(ix + 1), "alpha_low_" + suff, 20, 0.0, 0.5 * M_PI);
        book(_h_alpha_high->bin(ix + 1), "alpha_high_" + suff, 20, 0.0, 0.5 * M_PI);
      }
      book(_h_alpha_large, "_h_alpha_large", 20, 0., 0.5 * M_PI);
      book(_h_alpha_large_low, "_h_alpha_large_low", 20, 0., 0.5 * M_PI);
      book(_h_alpha_large_high, "_h_alpha_large_high", 20, 0., 0.5 * M_PI);
    }

    pair<double, double> calcRho(Histo1DPtr hist, unsigned int imode) {
      if (hist->numEntries() == 0.) return make_pair(0., 0.);
      double sum1(0.), sum2(0.);
      for (const auto& bin : hist->bins()) {
        double Oi = bin.sumW();
        if (Oi == 0.) continue;
        double ai, bi;
        if (imode == 0) {
          ai = 0.25 * (bin.xMax() * (3. - sqr(bin.xMax())) - bin.xMin() * (3. - sqr(bin.xMin())));
          bi = 0.75 * (bin.xMin() * (1. - sqr(bin.xMin())) - bin.xMax() * (1. - sqr(bin.xMax())));
        }
        else {
          ai = 2. * (bin.xMax() - bin.xMin()) / M_PI;
          bi = 2. * (sin(2. * bin.xMax()) - sin(2. * bin.xMin())) / M_PI;
        }
        double Ei = bin.errW();
        sum1 += sqr(bi / Ei);
        sum2 += bi / sqr(Ei) * (Oi - ai);
      }
      return make_pair(sum2 / sum1, sqrt(1. / sum1));
    }


    void analyze(const Event& e) {
      // First, veto on leptonic events by requiring at least 4 charged FS particles
      const FinalState& fs = apply<FinalState>(e, "FS");
      const size_t numParticles = fs.particles().size();

      // Even if we only generate hadronic events, we still need a cut on numCharged >= 2.
      if (numParticles < 2) {
        MSG_DEBUG("Failed leptonic event cut");
        vetoEvent;
      }
      MSG_DEBUG("Passed leptonic event cut");

      // Get beams and average beam momentum
      const ParticlePair& beams = apply<Beam>(e, "Beams").beams();
      const double meanBeamMom = 0.5 * (beams.first.p3().mod() + beams.second.p3().mod());
      MSG_DEBUG("Avg beam momentum = " << meanBeamMom);
      Vector3 axis;
      if (beams.first.pid() > 0) {
        axis = beams.first.momentum().p3().unit();
      }
      else {
        axis = beams.second.momentum().p3().unit();
      }

      // Final state of unstable particles to get particle spectra
      const UnstableParticles& ufs = apply<UnstableParticles>(e, "UFS");

      for (const Particle& p : ufs.particles(Cuts::abspid == 313)) {
        double xp = p.p3().mod() / meanBeamMom;
        _histXeK0->fill(xp);
        int sign = p.pid() / 313;
        if (p.children().size() != 2) continue;
        Particle kaon;
        if (p.children()[0].pid() == sign * 321 && p.children()[1].pid() == -sign * 211) {
          kaon = p.children()[0];
        }
        else if (p.children()[1].pid() == sign * 321 && p.children()[0].pid() == -sign * 211) {
          kaon = p.children()[1];
        }
        else
          continue;
        // spin axes
        Vector3 e1z = p.momentum().p3().unit();
        Vector3 e1y = e1z.cross(axis).unit();
        Vector3 e1x = e1y.cross(e1z).unit();
        LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(p.momentum().betaVec());
        Vector3 axis1 = boost.transform(kaon.momentum()).p3().unit();
        double ctheta = e1z.dot(axis1);
        double phi = atan2(e1y.dot(axis1), e1x.dot(axis1));
        double alpha = abs(abs(phi) - 0.5 * M_PI);
        _h_ctheta->fill(xp, ctheta);
        _h_alpha->fill(xp, alpha);
        double cBeam = axis.dot(e1z);
        (cBeam < 0.5 ? _h_alpha_low : _h_alpha_high)->fill(xp, alpha);

        if (xp > 0.3) {
          _h_ctheta_large->fill(ctheta);
          _h_alpha_large->fill(alpha);
          (cBeam < 0.5 ? _h_alpha_large_low : _h_alpha_large_high)->fill(alpha);
        }
      }
    }


    /// Finalize
    void finalize() {
      scale(_histXeK0, 1. / sumOfWeights());
      const vector<double> x = {0., 0.01, 0.03, 0.10, 0.125, 0.14, 0.16, 0.20, 0.30, 0.40, 0.50, 0.70, 1.00};
      Estimate1DPtr h_rho00;
      book(h_rho00, 2, 1, 1);
      Estimate1DPtr h_rho_off;
      book(h_rho_off, 2, 1, 2);
      Estimate1DPtr h_ratio;
      book(h_ratio, 3, 1, 1);
      Estimate1DPtr h_off_low;
      book(h_off_low, 4, 1, 1);
      Estimate1DPtr h_off_high;
      book(h_off_high, 4, 1, 2);
      for (size_t ix = 0; ix < _h_ctheta->numBins(); ++ix) {
        // extract the rho00 component
        normalize(_h_ctheta->bin(ix + 1));
        pair<double, double> rho00 = calcRho(_h_ctheta->bin(ix + 1), 0);
        h_rho00->bin(ix + 1).set(rho00.first, rho00.second);

        // extract the rho 1 -1 component
        normalize(_h_alpha->bin(ix + 1));
        pair<double, double> rho_off = calcRho(_h_alpha->bin(ix + 1), 1);
        h_rho_off->bin(ix + 1).set(rho_off.first, rho_off.second);

        if (ix < 8) continue;

        // at large xp also the ratio
        size_t iy = ix - 8;
        double ratio = rho_off.first / (1. - rho00.first);
        double dr = ((rho_off.second - rho00.first * rho_off.second + rho_off.first * rho00.second))
            / sqr(1. - rho00.first);
        h_ratio->bin(iy + 1).set(ratio, dr);
        // rho 1 -1 for cos theta <0.5
        normalize(_h_alpha_low->bin(iy + 1));
        rho_off = calcRho(_h_alpha_low->bin(iy + 1), 1);
        h_off_low->bin(iy + 1).set(rho_off.first, rho_off.second);
        // rho 1 -1 for cos theta >0.5
        normalize(_h_alpha_high->bin(iy + 1));
        rho_off = calcRho(_h_alpha_high->bin(iy + 1), 1);
        h_off_high->bin(iy + 1).set(rho_off.first, rho_off.second);
      }
      // ratio for xp 0.3
      normalize(_h_ctheta_large);
      pair<double, double> rho00 = calcRho(_h_ctheta_large, 0);
      normalize(_h_alpha_large);
      pair<double, double> rho_off = calcRho(_h_alpha_large, 1);
      double ratio = rho_off.first / (1. - rho00.first);
      double dr = ((rho_off.second - rho00.first * rho_off.second + rho_off.first * rho00.second))
          / sqr(1. - rho00.first);
      Estimate1DPtr h_ratio_large;
      book(h_ratio_large, 3, 2, 1);
      h_ratio_large->bin(1).set(ratio, dr);
      // rho 1 -1 for xp >0.3 and cos theta < 0.5
      normalize(_h_alpha_large_low);
      rho_off = calcRho(_h_alpha_large_low, 1);
      book(h_off_low, 4, 2, 1);
      h_off_low->bin(1).set(rho_off.first, rho_off.second);
      // rho 1 -1 for xp >0.3 and cos theta > 0.5
      normalize(_h_alpha_large_high);
      rho_off = calcRho(_h_alpha_large_high, 1);
      book(h_off_high, 4, 2, 2);
      h_off_high->bin(1).set(rho_off.first, rho_off.second);
    }

    /// @}


  private:

    /// @{
    Histo1DPtr _histXeK0;
    Histo1DGroupPtr _h_ctheta, _h_alpha, _h_alpha_low, _h_alpha_high;
    Histo1DPtr _h_ctheta_large, _h_alpha_large, _h_alpha_large_low, _h_alpha_large_high;
    /// @}
  };


  RIVET_DECLARE_ALIASED_PLUGIN(OPAL_1997_I447146, OPAL_1997_S3608263);

}