Rivet analyses

title: BELLE_2008_I762013

Decay angles in $D_{s1}(2536)^+\to D^{*+}K^0$

Experiment: BELLE (KEKB)

Inspire ID: 762013

Status: UNVALIDATED

Authors: - Peter Richardson

References: - Phys.Rev. D77 (2008) 032001

Beams: e- e+

Beam energies: (5.3, 5.3)GeV

Run details: - e+e- to hadrons

Measurement of decay angles in the decay $D_{s1}(2536)^+\to D^{*+}K^0$ by BELLE.

Source code:BELLE_2008_I762013.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief D_s1 decay angles class BELLE_2008_I762013 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2008_I762013);


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

/// Book histograms and initialise projections before the run
void init() {
  // projections
  declare(UnstableParticles(), "UFS");
  // book histos
  book(_h_alpha, 1, 1, 1);
  book(_h_beta, 2, 1, 1);
  book(_h_gamma, 3, 1, 1);
}

bool isK0(int id) {
  return id == 310 || id == 130 || abs(id) == 311;
}

/// Perform the per-event analysis
void analyze(const Event& event) {
  static const int DsID = 10433;
  const UnstableParticles& ufs = apply<UnstableParticles>(event, "UFS");
  for (const Particle& p : ufs.particles(Cuts::abspid == DsID)) {
    // decay angle
    int sign = p.pid() / DsID;
    Particle Dstar, Kaon;
    if (p.children().size() != 2) continue;
    if (p.children()[0].pid() == sign * 413 && isK0(p.children()[1].pid())) {
      Dstar = p.children()[0];
      Kaon = p.children()[1];
    }
    else if (p.children()[1].pid() == sign * 413 && isK0(p.children()[0].pid())) {
      Kaon = p.children()[0];
      Dstar = p.children()[1];
    }
    else {
      continue;
    }
    // first boost to the D_s1 rest frame
    LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(p.momentum().betaVec());
    FourMomentum pDstar = boost1.transform(Dstar.momentum());
    double cTheta = pDstar.p3().unit().dot(p.momentum().p3().unit());
    _h_alpha->fill(cTheta);
    if (Dstar.children().size() != 2) continue;
    Particle D0, Pion;
    if (Dstar.children()[0].pid() == sign * 211 && Dstar.children()[1].pid() == sign * 421) {
      Pion = Dstar.children()[0];
      D0 = Dstar.children()[1];
    }
    else if (Dstar.children()[1].pid() == sign * 211 && Dstar.children()[0].pid() == sign * 421) {
      D0 = Dstar.children()[0];
      Pion = Dstar.children()[1];
    }
    else
      continue;
    // boost to D_s frame
    FourMomentum pD = boost1.transform(D0.momentum());
    FourMomentum pK = boost1.transform(Kaon.momentum());
    FourMomentum pPi = boost1.transform(Pion.momentum());
    // to D* rest frame
    LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pDstar.betaVec());
    Vector3 axis = pDstar.p3().unit();
    FourMomentum pp = boost2.transform(pD);
    // calculate angle
    double cThetap = pp.p3().unit().dot(axis);
    _h_gamma->fill(cThetap);
    // finally beta
    Vector3 n1 = pD.p3().cross(pPi.p3()).unit();
    Vector3 n2 = axis.cross(pK.p3()).unit();
    double beta = acos(n1.dot(n2));
    _h_beta->fill(beta);
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  normalize(_h_alpha);
  normalize(_h_beta);
  normalize(_h_gamma);
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h_alpha, _h_beta, _h_gamma;
/// @}

};

RIVET_DECLARE_PLUGIN(BELLE_2008_I762013);

} ```