Rivet analyses

title: BESIII_2026_I2893764

$\pi^\pm$ and $K^\pm$ spectra for $\sqrt{s}=2\to3.671\,$GeV

Experiment: BESIII (BEPC)

Inspire ID: 2893764

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.Lett. 135 (2025) 151901 - arXiv: 2502.16084

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- to hadrons

Charged pion and kaon momentum spectra for a range centre-of-mass energies between 2 and 3.671 GeV.

Source code:BESIII_2026_I2893764.cc

```c++ // -- C++ --

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

namespace Rivet {

/// @brief pi+- and K+- spectra class BESIII_2026_I2893764 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2026_I2893764);


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

/// Book histograms and initialise projections before the run
void init() {
  // projection
  declare(FinalState(Cuts::abspid == PID::PIPLUS || Cuts::abspid == PID::KPLUS), "FS");
  // find beam energy
  size_t ih = 1;
  for (double eVal : allowedEnergies()) {

    const string en = toString(round(eVal / MeV));
    if (isCompatibleWithSqrtS(eVal)) _sqs = en;

    book(_h[en + "_1"], 1, 1, ih);
    book(_h[en + "_2"], 2, 1, ih);
    book(_h[en + "_3"], 3, 1, ih);
    book(_h[en + "_4"], 4, 1, ih);
    book(_c[en], "_aux_sigma_" + en);
    ++ih;
  }
  raiseBeamErrorIf(_sqs.empty());
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  _c[_sqs]->fill();
  for (const Particle& p : apply<FinalState>(event, "FS").particles()) {
    const double pp = p.p3().mod();
    if (p.pid() == PID::PIPLUS)
      _h[_sqs + "_1"]->fill(pp);
    else if (p.pid() == PID::PIMINUS)
      _h[_sqs + "_2"]->fill(pp);
    else if (p.pid() == PID::KPLUS)
      _h[_sqs + "_3"]->fill(pp);
    else if (p.pid() == PID::KMINUS)
      _h[_sqs + "_4"]->fill(pp);
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  scale(_h, crossSectionPerEvent());
  scale(_c, crossSectionPerEvent());
  for (const auto& item : _c) {
    scale(_h[item.first + "_1"s], 1.0 / item.second->sumW());
    scale(_h[item.first + "_2"s], 1.0 / item.second->sumW());
    scale(_h[item.first + "_3"s], 1.0 / item.second->sumW());
    scale(_h[item.first + "_4"s], 1.0 / item.second->sumW());
  }
}

/// @}


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

};

RIVET_DECLARE_PLUGIN(BESIII_2026_I2893764);

} ```