Rivet analyses

title: BESIII_2018_I1674528

Positron momentum spectrum in semileptonic $\Lambda_c^+$ decay

Experiment: BESIII (BEPC)

Inspire ID: 1674528

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.Lett. 121 (2018) 25, 251801

Beams: e+ e-

Beam energies: (2.0, 2.0); (3.0, 3.0)GeV

Run details: - e+e -> hadrons

Measurement of the positron momentum spectrum in the lab frame for semileptonic $\Lambda_c^+$ decay.

Source code:BESIII_2018_I1674528.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief Semileptonic Lambda_c+ class BESIII_2018_I1674528 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2018_I1674528);


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

/// Book histograms and initialise projections before the run
void init() {
  // projections
  declare(UnstableParticles(Cuts::abspid == 4122), "UFS");
  // histos
  book(_h, 1, 1, 1);
}

void findDecayProducts(Particle parent, Particles& em, Particles& ep, Particles& nue, Particles& nueBar) {
  for (const Particle& p : parent.children()) {
    if (p.pid() == PID::EMINUS) {
      em.push_back(p);
    }
    else if (p.pid() == PID::EPLUS) {
      ep.push_back(p);
    }
    else if (p.pid() == PID::NU_E) {
      nue.push_back(p);
    }
    else if (p.pid() == PID::NU_EBAR) {
      nueBar.push_back(p);
    }
    else if (!PID::isHadron(p.pid())) {
      findDecayProducts(p, em, ep, nue, nueBar);
    }
  }
}

/// Perform the per-event analysis
void analyze(const Event& event) {
  for (const Particle& p : apply<UnstableParticles>(event, "UFS").particles()) {
    Particles em, ep, nue, nueBar;
    findDecayProducts(p, em, ep, nue, nueBar);
    if (em.size() == 1 && nueBar.size() == 1) {
      double pmod = em[0].momentum().p3().mod();
      _h->fill(pmod);
    }
    else if (ep.size() == 1 && nue.size() == 1) {
      double pmod = ep[0].momentum().p3().mod();
      _h->fill(pmod);
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  normalize(_h, 1., false);
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h;
/// @}

};

RIVET_DECLARE_PLUGIN(BESIII_2018_I1674528);

} ```