Rivet analyses

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

namespace Rivet {


  /// @brief D* poliarzation at 29 GeV
  class TPC_1991_I316132 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(TPC_1991_I316132);


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

    /// Book histograms and initialise projections before the run
    void init() {

      // Initialise and register projections
      declare(Beam(), "Beams");
      declare(UnstableParticles(), "UFS");

      // Book histograms
      book(_h_ctheta, {0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 1.0});
      for (auto& b : _h_ctheta->bins()) {
        const string name = "ctheta_" + std::to_string(b.index() - 1);
        book(b, name, 20, -1.0, 1.0);
      }
      book(_h_ctheta_all, "ctheta_all", 20, -1, 1);

      book(_h_phi, {0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 1.0});
      for (auto& b : _h_phi->bins()) {
        const string name = "phi_" + std::to_string(b.index() - 1);
        book(b, name, 20, -M_PI, M_PI);
      }
      book(_h_phi_all, "phi_all", 20, -M_PI, M_PI);

      book(_h_01, {0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 1.0});
      for (auto& b : _h_01->bins()) {
        const string name = "h_01_" + std::to_string(b.index() - 1);
        book(b, name, 20, -1.0, 1.0);
      }
      book(_h_01_all, "h_01_all", 20, -1, 1);
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      // Get beams and average beam momentum
      const ParticlePair& beams = apply<Beam>(event, "Beams").beams();
      const double Emax = (beams.first.p3().mod() + beams.second.p3().mod()) / 2.0;
      Vector3 axis;
      if (beams.first.pid() > 0) {
        axis = beams.first.momentum().p3().unit();
      }
      else {
        axis = beams.second.momentum().p3().unit();
      }

      const UnstableParticles& ufs = apply<UnstableParticles>(event, "UFS");
      for (const Particle& p : ufs.particles(Cuts::abspid == 413)) {
        if (p.children().size() != 2) continue;
        int sign = p.pid() / 413;
        Particle D0;
        if (p.children()[0].pid() == sign * 421 && p.children()[1].pid() == sign * 211) {
          D0 = p.children()[0];
        }
        else if (p.children()[1].pid() == sign * 421 && p.children()[0].pid() == sign * 211) {
          D0 = p.children()[1];
        }
        else {
          continue;
        }
        LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(p.momentum().betaVec());
        const double xE = p.momentum().t() / Emax;
        Vector3 e1z = p.momentum().p3().unit();
        Vector3 e1y = e1z.cross(axis).unit();
        Vector3 e1x = e1y.cross(e1z).unit();
        Vector3 axis1 = boost.transform(D0.momentum()).p3().unit();
        const double ctheta = e1z.dot(axis1);
        _h_ctheta->fill(xE, ctheta);
        const double phi = atan2(e1y.dot(axis1), e1x.dot(axis1));
        _h_phi->fill(xE, phi);
        _h_01->fill(xE, ctheta, cos(phi));

        if (xE > 0.3) {
          _h_ctheta_all->fill(ctheta);
          _h_phi_all->fill(phi);
          _h_01_all->fill(ctheta, cos(phi));
        }
      }
    }

    pair<double, double> calcRho(Histo1DPtr hist, unsigned int mode) {
      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 (mode == 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 if (mode == 1) {
          ai = 0.5 / M_PI * (bin.xMax() - bin.xMin());
          bi = 0.5 / M_PI * (sin(2. * bin.xMin()) - sin(2. * bin.xMax()));
        }
        else {
          ai = 0.;
          bi = sqrt(0.5)
              * ((1. - sqr(bin.xMax())) * sqrt(1. - sqr(bin.xMax()))
                 - (1. - sqr(bin.xMin())) * sqrt(1. - sqr(bin.xMin())));
        }
        double Ei = bin.errW();
        sum1 += sqr(bi / Ei);
        sum2 += bi / sqr(Ei) * (Oi - ai);
      }
      return make_pair(sum2 / sum1, sqrt(1. / sum1));
    }

    pair<double, pair<double, double>> calcAlpha(Histo1DPtr hist) {
      if (hist->numEntries() == 0.) return make_pair(0., make_pair(0., 0.));
      double d = 3. / (pow(hist->xMax(), 3) - pow(hist->xMin(), 3));
      double c = 3. * (hist->xMax() - hist->xMin()) / (pow(hist->xMax(), 3) - pow(hist->xMin(), 3));
      double sum1(0.), sum2(0.), sum3(0.), sum4(0.), sum5(0.);
      for (const auto& bin : hist->bins()) {
        double Oi = bin.sumW();
        if (Oi == 0.) continue;
        double a = d * (bin.xMax() - bin.xMin());
        double b = d / 3. * (pow(bin.xMax(), 3) - pow(bin.xMin(), 3));
        double Ei = bin.errW();
        sum1 += a * Oi / sqr(Ei);
        sum2 += b * Oi / sqr(Ei);
        sum3 += sqr(a) / sqr(Ei);
        sum4 += sqr(b) / sqr(Ei);
        sum5 += a * b / sqr(Ei);
      }
      // calculate alpha
      double alpha = (-c * sum1 + sqr(c) * sum2 + sum3 - c * sum5) / (sum1 - c * sum2 + c * sum4 - sum5);
      // and error
      double cc = -pow((sum3 + sqr(c) * sum4 - 2 * c * sum5), 3);
      double bb = -2 * sqr(sum3 + sqr(c) * sum4 - 2 * c * sum5) * (sum1 - c * sum2 + c * sum4 - sum5);
      double aa = sqr(sum1 - c * sum2 + c * sum4 - sum5)
          * (-sum3 - sqr(c) * sum4 + sqr(sum1 - c * sum2 + c * sum4 - sum5) + 2 * c * sum5);
      double dis = sqr(bb) - 4. * aa * cc;
      if (dis > 0.) {
        dis = sqrt(dis);
        return make_pair(alpha, make_pair(0.5 * (-bb + dis) / aa, -0.5 * (-bb - dis) / aa));
      }
      else {
        return make_pair(alpha, make_pair(0., 0.));
      }
    }

    /// Normalise histograms etc., after the run
    void finalize() {
      Estimate1DPtr h_alpha, h_rho00, h_rhooff, h_01;
      book(h_alpha, 1, 1, 1);
      book(h_rho00, 2, 1, 1);
      book(h_rhooff, 2, 1, 2);
      book(h_01, 2, 1, 3);
      for (size_t ix = 1; ix < _h_ctheta->numBins() + 1; ++ix) {
        const double integral = _h_ctheta->bin(ix)->integral();
        scale(_h_ctheta->bin(ix), 1. / integral);
        scale(_h_01->bin(ix), 1. / integral);
        normalize(_h_phi->bin(ix));

        pair<double, double> rho00 = calcRho(_h_ctheta->bin(ix), 0);
        h_rho00->bin(ix).set(rho00.first, rho00.second);

        pair<double, pair<double, double>> alpha = calcAlpha(_h_ctheta->bin(ix));
        h_alpha->bin(ix).set(alpha.first, alpha.second);

        pair<double, double> rhooff = calcRho(_h_phi->bin(ix), 1);
        h_rhooff->bin(ix).set(rhooff.first, rhooff.second);

        pair<double, double> rho01 = calcRho(_h_01->bin(ix), 2);
        h_01->bin(ix).set(rho01.first, rho01.second);
      }
      // integral over z
      double integral = _h_ctheta_all->integral();
      scale(_h_ctheta_all, 1. / integral);
      scale(_h_01_all, 1. / integral);
      normalize(_h_phi_all);

      pair<double, double> rho00 = calcRho(_h_ctheta_all, 0);
      h_rho00->bin(7).set(rho00.first, rho00.second);

      pair<double, pair<double, double>> alpha = calcAlpha(_h_ctheta_all);
      h_alpha->bin(7).set(alpha.first, alpha.second);

      pair<double, double> rhooff = calcRho(_h_phi_all, 1);
      h_rhooff->bin(7).set(rhooff.first, rhooff.second);

      pair<double, double> rho01 = calcRho(_h_01_all, 2);
      h_01->bin(7).set(rho01.first, rho01.second);
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DGroupPtr _h_ctheta, _h_phi, _h_01;
    Histo1DPtr _h_ctheta_all, _h_phi_all, _h_01_all;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(TPC_1991_I316132);


}