Rivet analyses

title: BELLE_2012_I1123656

Helicity angles in $B^0\to D^{+}D^{-}$

Experiment: BELLE (KEKB)

Inspire ID: 1123656

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 86 (2012) 071103

Beams: * *

Beam energies: ANY

Run details: - Any process producing B0, original Upsilon(4S) decay

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

Source code:BELLE_2012_I1123656.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief B0 -> D+ D- class BELLE_2012_I1123656 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2012_I1123656);


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

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  UnstableParticles ufs = UnstableParticles(Cuts::abspid == 511);
  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 B0 = apply<UnstableParticles>(event, "UFS").particles();
  for (const Particle& p : B0) {
    if (p.children().size() != 2) continue;
    if (p.children()[0].pid() != -p.children()[1].pid()) continue;
    if (p.children()[0].abspid() != 413) 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);
    // find children of the D mesons
    Particle pip, pim;
    if (Dp.children().size() != 2) continue;
    if (Dp.children()[0].abspid() == PID::PIPLUS && Dp.children()[1].abspid() == PID::D0)
      pip = Dp.children()[0];
    else if (Dp.children()[1].abspid() == PID::PIPLUS && Dp.children()[0].abspid() == PID::D0)
      pip = Dp.children()[1];
    else
      continue;
    if (Dm.children().size() != 2) continue;
    if (Dm.children()[0].abspid() == PID::PIPLUS && Dm.children()[1].abspid() == PID::D0) {
      pim = Dm.children()[0];
    }
    else if (Dm.children()[1].abspid() == PID::PIPLUS && Dm.children()[0].abspid() == PID::D0) {
      pim = Dm.children()[1];
    }
    else
      continue;
    // boost to rest frame
    LorentzTransform boostB = LorentzTransform::mkFrameTransformFromBeta(p.momentum().betaVec());
    FourMomentum pDstarPlus = boostB.transform(Dp.momentum());
    FourMomentum pDstarMinus = boostB.transform(Dm.momentum());
    LorentzTransform boostDp = LorentzTransform::mkFrameTransformFromBeta(pDstarPlus.betaVec());
    FourMomentum ppip = boostDp.transform(boostB.transform(pip.momentum()));
    LorentzTransform boostDm = LorentzTransform::mkFrameTransformFromBeta(pDstarMinus.betaVec());
    FourMomentum ppim = boostDm.transform(boostB.transform(pim.momentum()));
    Vector3 axisX = pDstarPlus.p3().unit();
    // ctheta1
    _h[1]->fill(axisX.dot(ppim.p3().unit()));
    // y and z axis
    ppim = boostDp.transform(boostB.transform(pim.momentum()));
    Vector3 axisZ = axisX.cross(ppim.p3()).unit();
    // cThetaTr
    _h[0]->fill(axisZ.dot(ppip.p3().unit()));
  }
}


/// 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_2012_I1123656);

} ```