Rivet analyses

title: BESIII_2019_I1702549

$D_s^+\to K^0 e^+\nu_e$ $q^2$ spectrum $D_s^+\to K^{*0} e^+\nu_e$ $q^2$ distributions

Experiment: BESIII (BEPC)

Inspire ID: 1702549

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Rev.Lett. 122 (2019) 6, 061801

Beams: * *

Beam energies: ANY

Run details: - Any process producing D_s+

Measurement of the $q^2$ spectrum in the decay $D_s^+\to K^0 e^+\nu_e$ and kinematic distributions in $D_s^+\to K^{*0} e^+\nu_e$ $q^2$ by BES-III. N.B. the plots where read from the paper and may not have been corrected for acceptance.

Source code:BESIII_2019_I1702549.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief q^2 in D_s+ -> K0 e+ nu_e and ->K*0 e+ nu_e distributions class BESIII_2019_I1702549 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2019_I1702549);


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

/// Book histograms and initialise projections before the run
void init() {

  // Initialise and register projections
  UnstableParticles ufs = UnstableParticles(Cuts::pid == 431);
  declare(ufs, "UFS");
  DecayedParticles DS(ufs);
  DS.addStable(PID::PI0);
  DS.addStable(PID::K0S);
  DS.addStable(PID::ETA);
  DS.addStable(PID::ETAPRIME);
  declare(DS, "DS");

  // Book histograms
  book(_h_q2, 1, 1, 1);
  book(_nD, "/TMP/nD");
  for (unsigned int ix = 0; ix < 5; ++ix) book(_h_Kstar[ix], 1, 1, 3 + ix);
}

/// Perform the per-event analysis
void analyze(const Event& event) {
  static const map<PdgId, unsigned int>& mode1 = {{310, 1}, {-11, 1}, {12, 1}};
  static const map<PdgId, unsigned int>& mode2 = {{130, 1}, {-11, 1}, {12, 1}};
  static const map<PdgId, unsigned int>& mode3 = {{311, 1}, {-11, 1}, {12, 1}};
  static const map<PdgId, unsigned int>& mode4 = {{321, 1}, {-211, 1}, {-11, 1}, {12, 1}};
  DecayedParticles DS = apply<DecayedParticles>(event, "DS");
  // loop over particles
  for (unsigned int ix = 0; ix < DS.decaying().size(); ++ix) {
    _nD->fill();
    if (DS.modeMatches(ix, 3, mode1)) {
      _h_q2->fill((DS.decaying()[ix].momentum() - DS.decayProducts()[ix].at(310)[0].momentum()).mass2());
    }
    else if (DS.modeMatches(ix, 3, mode2)) {
      _h_q2->fill((DS.decaying()[ix].momentum() - DS.decayProducts()[ix].at(130)[0].momentum()).mass2());
    }
    else if (DS.modeMatches(ix, 3, mode3)) {
      _h_q2->fill((DS.decaying()[ix].momentum() - DS.decayProducts()[ix].at(311)[0].momentum()).mass2());
    }
    else if (DS.modeMatches(ix, 4, mode4)) {
      const Particle& Kp = DS.decayProducts()[ix].at(321)[0];
      const Particle& pim = DS.decayProducts()[ix].at(-211)[0];
      const Particle& ep = DS.decayProducts()[ix].at(-11)[0];
      const Particle& nue = DS.decayProducts()[ix].at(12)[0];
      FourMomentum pKstar = Kp.momentum() + pim.momentum();
      _h_Kstar[0]->fill(pKstar.mass());
      FourMomentum qq = DS.decaying()[ix].momentum() - pKstar;
      _h_Kstar[1]->fill(qq.mass2());
      // boost momenta to Ds rest frame
      LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(
          DS.decaying()[ix].momentum().betaVec());
      FourMomentum pKS = boost.transform(pKstar);
      Matrix3 ptoz(-pKS.p3().unit(), Vector3(0, 0, 1));
      boost.preMult(ptoz);
      // the momenta in frane to W along z
      FourMomentum pD = boost.transform(DS.decaying()[ix].momentum());
      FourMomentum pK = boost.transform(Kp.momentum());
      FourMomentum ppi = boost.transform(pim.momentum());
      FourMomentum pe = boost.transform(ep.momentum());
      FourMomentum pnu = boost.transform(nue.momentum());
      pKstar = pK + ppi;
      qq = pD - pKstar;
      LorentzTransform boostK = LorentzTransform::mkFrameTransformFromBeta(pKstar.betaVec());
      Vector3 axisK = boostK.transform(pK).p3().unit();
      _h_Kstar[3]->fill(axisK.dot(pKstar.p3().unit()));
      LorentzTransform boostW = LorentzTransform::mkFrameTransformFromBeta(qq.betaVec());
      Vector3 axisE = boostW.transform(pe).p3().unit();
      _h_Kstar[2]->fill(axisE.dot(qq.p3().unit()));
      axisK.setZ(0.);
      axisE.setZ(0.);
      double chi = atan2(axisE.cross(axisK).dot(qq.p3().unit()), axisE.dot(axisK));
      _h_Kstar[4]->fill(chi);
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  // normalise to width in inverse ns
  scale(_h_q2, 1. / 0.504e-3 / *_nD);
  for (unsigned int ix = 0; ix < 5; ++ix) {
    normalize(_h_Kstar[ix]);
  }
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h_q2;
Histo1DPtr _h_Kstar[5];
CounterPtr _nD;
/// @}

};

RIVET_DECLARE_PLUGIN(BESIII_2019_I1702549);

} ```