Rivet analyses

// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/Beam.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Tools/Random.hh"

namespace Rivet {


  /// @brief Collins assymmetry
  class BESIII_2016_I1384778 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2016_I1384778);


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

    /// Book histograms and initialise projections before the run
    void init() {
      declare(Beam(), "Beams");
      declare(FinalState(Cuts::abspid == PID::PIPLUS), "FS");
      // book the histograms
      _h_L.resize(6);
      _h_U.resize(6);
      _h_C.resize(6);
      for (size_t ix = 0; ix < _h_L.size(); ++ix) {
        const string pre = "/TMP/h_z1z2_" + to_string(ix + 1);
        book(_h_L[ix], pre + "_L", 20, 0., M_PI);
        book(_h_U[ix], pre + "_U", 20, 0., M_PI);
        book(_h_C[ix], pre + "_C", 20, 0., M_PI);
      }
      book(_h_pT_L, {0., 0.2, 0.3, 0.45, 0.8, 1.4});
      book(_h_pT_U, {0., 0.2, 0.3, 0.45, 0.8, 1.4});
      book(_h_pT_C, {0., 0.2, 0.3, 0.45, 0.8, 1.4});
      for (size_t ix = 1; ix < _h_pT_L->numBins() + 1; ++ix) {
        const string pre = "/TMP/h_pT_" + to_string(ix);
        book(_h_pT_L->bin(ix), pre + "_L", 20, 0.0, M_PI);
        book(_h_pT_U->bin(ix), pre + "_U", 20, 0.0, M_PI);
        book(_h_pT_C->bin(ix), pre + "_C", 20, 0.0, M_PI);
      }
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      // get the axis, direction of incoming electron
      const ParticlePair& beams = apply<Beam>(event, "Beams").beams();
      Vector3 axis;
      if (beams.first.pid() > 0) {
        axis = beams.first.momentum().p3().unit();
      }
      else {
        axis = beams.second.momentum().p3().unit();
      }
      // loop over pions pair, using index to avoid double counting
      Particles pions = apply<FinalState>(event, "FS").particles();
      for (unsigned int i1 = 0; i1 < pions.size(); ++i1) {
        const double x1 = 2. * pions[i1].momentum().t() / sqrtS();
        // cut on z1
        if (x1 < 0.2 || x1 > 0.9) continue;
        // cos theta cut
        if (abs(cos(pions[i1].momentum().p3().polarAngle())) > 0.93) continue;
        for (unsigned int i2 = i1 + 1; i2 < pions.size(); ++i2) {
          // cut on z2
          const double x2 = 2. * pions[i2].momentum().t() / sqrtS();
          if (x2 < 0.2 || x2 > 0.9) continue;
          // cos theta cut
          if (abs(cos(pions[i2].momentum().p3().polarAngle())) > 0.93) continue;
          // cut on opening angle (>120 degrees)
          if (pions[i1].momentum().p3().angle(pions[i2].momentum().p3()) > 2. * M_PI / 3.) {
            continue;
          }
          Particle p1 = pions[i1], p2 = pions[i2];
          double z1(x1), z2(x2);
          // randomly order the particles
          if (rand01() < 0.5) {
            swap(p1, p2);
            swap(z1, z2);
          }
          // particle 2 defines the z axis
          Vector3 ez = p2.momentum().p3().unit();
          // beam and 2 define the plane (y is normal to plane)
          Vector3 ey = ez.cross(axis).unit();
          // x by cross product
          Vector3 ex = ey.cross(ez).unit();
          // phi
          double phi = ex.angle(p1.momentum().p3());
          // hists vs z1,z2
          unsigned int ibin = 0;
          if (z1 <= .3 && z2 <= .3) {
            ibin = 0;
          }
          else if (z1 > 0.5 && z2 > 0.5) {
            ibin = 5;
          }
          else if (min(z1, z2) <= 0.3) {
            if (max(z1, z2) > 0.5) {
              ibin = 2;
            }
            else {
              ibin = 1;
            }
          }
          else {
            if (max(z1, z2) > 0.5) {
              ibin = 4;
            }
            else {
              ibin = 3;
            }
          }
          _h_C[ibin]->fill(phi);
          if (p1.pid() == p2.pid()) {
            _h_L[ibin]->fill(phi);
          }
          else {
            _h_U[ibin]->fill(phi);
          }
          // hists vs pT
          double pPar2 = sqr(ez.dot(p1.momentum().p3()));
          double pPerp = sqrt(p1.momentum().p3().mod2() - pPar2);
          _h_pT_C->fill(pPerp, phi);
          if (p1.pid() == p2.pid()) {
            _h_pT_L->fill(pPerp, phi);
          }
          else {
            _h_pT_U->fill(pPerp, phi);
          }
        }
      }
    }

    pair<double, double> calcAsymmetry(Estimate1DPtr hist) {
      double sum1(0.), sum2(0.);
      for (const auto& b : hist->bins()) {
        double Oi = b.val();
        if (Oi == 0. || std::isnan(Oi)) continue;
        double ai = 1.;
        double bi = 0.5 * (sin(2. * b.xMax()) - sin(2. * b.xMin())) / b.xWidth();
        double Ei = b.errAvg();
        sum1 += sqr(bi / Ei);
        sum2 += bi / sqr(Ei) * (Oi - ai);
      }
      return make_pair(sum2 / sum1, sqrt(1. / sum1));
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      // ratios
      BinnedEstimatePtr<string> _h_z_UL, _h_z_UC;
      book(_h_z_UL, 1, 1, 5);
      book(_h_z_UC, 1, 1, 6);
      for (size_t ix = 0; ix < _h_L.size(); ++ix) {
        normalize(_h_L[ix]);
        normalize(_h_U[ix]);
        normalize(_h_C[ix]);
        const string pre = "/TMP/R_z1z2_" + to_string(ix + 1);
        Estimate1DPtr R1;
        book(R1, pre + "_UL", 20, 0., M_PI);
        divide(_h_U[ix], _h_L[ix], R1);
        Estimate1DPtr R2;
        book(R2, pre + "_UC", 20, 0., M_PI);
        divide(_h_U[ix], _h_C[ix], R2);
        pair<double, double> asym1 = calcAsymmetry(R1);
        _h_z_UL->bin(ix + 1).set(asym1.first, asym1.second);
        pair<double, double> asym2 = calcAsymmetry(R2);
        _h_z_UC->bin(ix + 1).set(asym2.first, asym2.second);
      }
      Estimate1DPtr _h_pT_UL, _h_pT_UC;
      book(_h_pT_UL, 2, 1, 4);
      book(_h_pT_UC, 2, 1, 5);
      for (size_t ix = 1; ix < _h_pT_L->numBins() + 1; ++ix) {
        normalize(_h_pT_L->bin(ix));
        normalize(_h_pT_U->bin(ix));
        normalize(_h_pT_C->bin(ix));
        const string pre = "/TMP/R_pT_" + to_string(ix);
        Estimate1DPtr R1;
        book(R1, pre + "_UL", 20, 0., M_PI);
        divide(_h_pT_U->bin(ix), _h_pT_L->bin(ix), R1);
        Estimate1DPtr R2;
        book(R2, pre + "_UC", 20, 0., M_PI);
        divide(_h_pT_U->bin(ix), _h_pT_C->bin(ix), R2);
        pair<double, double> asym1 = calcAsymmetry(R1);
        _h_pT_UL->bin(ix).set(asym1.first, asym1.second);
        pair<double, double> asym2 = calcAsymmetry(R2);
        _h_pT_UC->bin(ix).set(asym2.first, asym2.second);
      }
    }
    /// @}


    /// @name Histograms
    /// @{
    vector<Histo1DPtr> _h_L, _h_U, _h_C;
    Histo1DGroupPtr _h_pT_L, _h_pT_U, _h_pT_C;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BESIII_2016_I1384778);

}