Rivet analyses

title: BELLE_2013_I1124584

Helicity angles in $B_s^0\to D_s^{+}D_s^{-}$

Experiment: BELLE (KEKB)

Inspire ID: 1124584

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 87 (2013) 3, 031101

Beams: * *

Beam energies: ANY

Run details: - Any process producing B_s0, original Upsilon(5S) decay

Helicity angle distributions in $B^0\to D^{+}D^{-}$ decays

Source code:BELLE_2013_I1124584.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief Bs0 -> Ds Ds class BELLE_2013_I1124584 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2013_I1124584);


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

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  UnstableParticles ufs = UnstableParticles(Cuts::abspid == 531);
  declare(ufs, "UFS");
  // histograms
  for (unsigned int ix = 0; ix < 2; ++ix) book(_h[ix], 1, 1, 1 + ix);
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  Particles BS0 = apply<UnstableParticles>(event, "UFS").particles();
  for (const Particle& p : BS0) {
    if (p.children().size() != 2) continue;
    if (p.children()[0].pid() != -p.children()[1].pid()) continue;
    if (p.children()[0].abspid() != 433) continue;
    Particle Dp = p.children()[0];
    Particle Dm = p.children()[1];
    if (p.pid() > 0 && Dp.pid() < 0)
      swap(Dp, Dm);
    else if (p.pid() < 0 && Dp.pid() > 0)
      swap(Dp, Dm);
    // boost to rest frame
    LorentzTransform boostB = LorentzTransform::mkFrameTransformFromBeta(p.momentum().betaVec());
    FourMomentum pB = boostB.transform(p.momentum());
    if (Dp.children().size() == 2) {
      Particle gamma;
      bool found = true;
      if (Dp.children()[0].pid() == PID::GAMMA && Dp.children()[1].abspid() == 431)
        gamma = Dp.children()[0];
      else if (Dp.children()[1].pid() == PID::GAMMA && Dp.children()[0].abspid() == 431)
        gamma = Dp.children()[1];
      else
        found = false;
      if (found) {
        FourMomentum pD = boostB.transform(Dp.momentum());
        FourMomentum pgamma = boostB.transform(gamma.momentum());
        LorentzTransform boostD = LorentzTransform::mkFrameTransformFromBeta(pD.betaVec());
        Vector3 axisB = boostD.transform(pB).p3().unit();
        Vector3 axisG = boostD.transform(pgamma).p3().unit();
        _h[0]->fill(axisB.dot(axisG));
      }
    }
    if (Dm.children().size() == 2) {
      Particle gamma;
      bool found = true;
      if (Dm.children()[0].pid() == PID::GAMMA && Dm.children()[1].abspid() == 431)
        gamma = Dm.children()[0];
      else if (Dm.children()[1].pid() == PID::GAMMA && Dm.children()[0].abspid() == 431)
        gamma = Dm.children()[1];
      else
        found = false;
      if (found) {
        FourMomentum pD = boostB.transform(Dm.momentum());
        FourMomentum pgamma = boostB.transform(gamma.momentum());
        LorentzTransform boostD = LorentzTransform::mkFrameTransformFromBeta(pD.betaVec());
        Vector3 axisB = boostD.transform(pB).p3().unit();
        Vector3 axisG = boostD.transform(pgamma).p3().unit();
        _h[1]->fill(axisB.dot(axisG));
      }
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  for (unsigned int ix = 0; ix < 2; ++ix) normalize(_h[ix], 1., false);
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h[2];
/// @}

};

RIVET_DECLARE_PLUGIN(BELLE_2013_I1124584);

} ```