Rivet analyses

η spectra for various energies between 2 and 3.671 GeV

Experiment: BESIII (BEPC)

Inspire ID: 2753516

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.Lett. 133 (2024) 2, 021901 - arXiv: 2401.17873

Beams: e+ e-

Beam energies: (1.0, 1.0); (1.1, 1.1); (1.2, 1.2); (1.3, 1.3); (1.4, 1.4); (1.5, 1.5); (1.8, 1.8); (1.8, 1.8)GeV

Run details: - e+e- > hadrons

Measurement of the momentum spectrum for η production in e+e− collisions at low energies by BES.

Source code:BESIII_2024_I2753516.cc

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

namespace Rivet {


  /// @brief eta spectra
  class BESIII_2024_I2753516 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2024_I2753516);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      declare(UnstableParticles(Cuts::pid==221), "UFS");
      // histos
      size_t ih = 1;
      for (double eVal : allowedEnergies()) {

        const string en = toString(round(eVal/MeV));
        if (isCompatibleWithSqrtS(eVal))  _sqs = en;
        book(_c[en], "_aux_sigma_"+en);
        book(_h[en],1,1,ih);
        ++ih;
      }
      raiseBeamErrorIf(_sqs.empty());
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      _c[_sqs]->fill();
      const UnstableParticles& ufs = apply<UnstableParticles>(event, "UFS");
      for (const Particle& p : ufs.particles()) {
        _h[_sqs]->fill(p.mom().p3().mod());
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      scale(_h, crossSectionPerEvent());
      scale(_c, crossSectionPerEvent());
      for (const auto& item : _c) {
        if (isZero(item.second->sumW()))  continue;
        scale(_h[item.first], 1.0/item.second->sumW());
      }
    }

    /// @}


    /// @name Histograms
    /// @{
    map<string,Histo1DPtr> _h;
    map<string,CounterPtr> _c;
    string _sqs = "";
    /// @}


  };


  RIVET_DECLARE_PLUGIN(BESIII_2024_I2753516);

}