Rivet analyses

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

namespace Rivet {


  /// @brief J/Psi and Psi(2S) spectra at the Upsilon(4S)
  class CLEOII_2002_I606309 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(CLEOII_2002_I606309);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // projections
      declare(UnstableParticles(), "UFS");
      //histograms
      book(_weightSum, "/TMP/weightSum");
      book(_h_Jpsi, 3, 1, 1);
      book(_h_Psi_prime, 3, 1, 2);
      book(_h_cTheta_Jpsi, 4, 1, 1);
      book(_h_cTheta_Psi_prime, 4, 1, 2);
      book(_h2_cTheta_Jpsi, {0., 0.8, 1.4, 2.});
      for (auto& b : _h2_cTheta_Jpsi->bins()) {
        book(b, "/TMP/ctheta_" + to_string(b.index() - 1), 20, -1.0, 1.0);
      }
    }

    void findDecayProducts(Particle parent, Particles& charm) {
      for (const Particle& p : parent.children()) {
        if (p.pid() == 443) {
          charm.push_back(p);
          continue;
        }
        else if (p.pid() == 100443) {
          charm.push_back(p);
        }
        if (!p.children().empty()) {
          findDecayProducts(p, charm);
        }
      }
    }

    void findLeptons(const Particle& mother, unsigned int& nstable, Particles& lp, Particles& lm) {
      for (const Particle& p : mother.children()) {
        int id = p.pid();
        if (id == 11 || id == 13) {
          lm.push_back(p);
          ++nstable;
        }
        else if (id == -11 || id == -13) {
          lp.push_back(p);
          ++nstable;
        }
        else if (!p.children().empty()) {
          findLeptons(p, nstable, lp, lm);
        }
        else {
          ++nstable;
        }
      }
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      const UnstableParticles& ufs = apply<UnstableParticles>(event, "UFS");
      for (const Particle& p : ufs.particles(Cuts::pid == 300553)) {
        _weightSum->fill();
        const LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(p.momentum().betaVec());
        Particles charm;
        findDecayProducts(p, charm);
        for (const Particle& pp : charm) {
          FourMomentum pcm = boost.transform(pp.momentum());
          unsigned int nstable = 0;
          Particles lp, lm;
          findLeptons(pp, nstable, lp, lm);
          double cTheta(0.);
          bool foundLeptons(false);
          if (nstable == 2 && lp.size() == 1 && lm.size() == 1) {
            foundLeptons = true;
            FourMomentum pl = boost.transform(lm[0].momentum());
            const LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pcm.betaVec());
            pl = boost2.transform(pl);
            cTheta = pl.p3().unit().dot(pcm.p3().unit());
          }
          if (pp.pid() == 443) {
            _h_Jpsi->fill(pcm.p3().mod());
            if (foundLeptons) {
              _h_cTheta_Jpsi->fill(cTheta);
              _h2_cTheta_Jpsi->fill(pcm.p3().mod(), cTheta);
            }
          }
          else {
            _h_Psi_prime->fill(pcm.p3().mod());
            if (foundLeptons) {
              _h_cTheta_Psi_prime->fill(cTheta);
            }
          }
        }
      }
    }

    pair<double, pair<double, double>> calcAlpha(const 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() {
      if (_weightSum->val() == 0.) return;
      scale(_h_Jpsi, 50. / *_weightSum);
      scale(_h_Psi_prime, 50. / *_weightSum);
      // polarization J/psi
      normalize(_h_cTheta_Jpsi);
      pair<double, pair<double, double>> alpha = calcAlpha(_h_cTheta_Jpsi);
      Estimate1DPtr _h_alpha;
      book(_h_alpha, 1, 1, 1);
      _h_alpha->bin(1).set(alpha.first, alpha.second);
      // polarization psi(2S)
      normalize(_h_cTheta_Psi_prime);
      alpha = calcAlpha(_h_cTheta_Psi_prime);
      book(_h_alpha, 1, 1, 2);
      _h_alpha->bin(1).set(alpha.first, alpha.second);

      // J/psi as function of momentum
      book(_h_alpha, 2, 1, 1);
      for (auto& b : _h2_cTheta_Jpsi->bins()) {
        normalize(b);
        alpha = calcAlpha(b);
        _h_alpha->bin(b.index()).set(alpha.first, alpha.second);
      }
    }

    /// @}


    /// @name Histograms
    /// @{
    // count of weights
    CounterPtr _weightSum;
    // histograms
    Histo1DPtr _h_Jpsi, _h_Psi_prime;
    Histo1DPtr _h_cTheta_Jpsi, _h_cTheta_Psi_prime;
    Histo1DGroupPtr _h2_cTheta_Jpsi;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(CLEOII_2002_I606309);

}