Rivet analyses

title: BELLE_2005_I677084

Helicity angle in $B^-\to D^0 D^{*-}$

Experiment: BELLE (KEKB)

Inspire ID: 677084

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.Lett. 95 (2005) 041803

Beams: * *

Beam energies: ANY

Run details: - Any process producing B+- mesons, originally Upsilon(4S) decays

Measurement of the helicity angle distribution in $B^-\to D^0 D^{*-}$ decays. The background subtracted data were read from Figure 2 in the paper.

Source code:BELLE_2005_I677084.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief B- -> D0 D*- class BELLE_2005_I677084 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2005_I677084);


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

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

  // Initialise and register projections
  declare(UnstableParticles(Cuts::abspid == 521), "UFS");

  // Book histograms
  book(_h_cTheta, 1, 1, 1);
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  // Loop over B0 mesons
  for (const Particle& p : apply<UnstableParticles>(event, "UFS").particles()) {
    // find the B decay
    int sign = p.pid() / p.abspid();
    if (p.children().size() != 2) continue;
    Particle Dstar;
    if (p.children()[0].pid() == sign * 413 && p.children()[1].pid() == -sign * 421) {
      Dstar = p.children()[0];
    }
    else if (p.children()[1].pid() == sign * 413 && p.children()[0].pid() == -sign * 421) {
      Dstar = p.children()[1];
    }
    else {
      continue;
    }
    // and the D* decay
    if (Dstar.children().size() != 2) continue;
    Particle pip;
    if (Dstar.children()[0].pid() == sign * 421 && Dstar.children()[1].pid() == sign * 211) {
      pip = Dstar.children()[1];
    }
    else if (Dstar.children()[1].pid() == sign * 421 && Dstar.children()[0].pid() == sign * 211) {
      pip = Dstar.children()[0];
    }
    else {
      continue;
    }
    // compute the helicity angle
    // boost to B+ rest frame
    LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(p.momentum().betaVec());
    FourMomentum pDstar = boost1.transform(Dstar.momentum());
    FourMomentum pPi = boost1.transform(pip.momentum());
    LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pDstar.betaVec());
    pPi = boost2.transform(pPi);
    const double cTheta = pPi.p3().unit().dot(pDstar.p3().unit());
    _h_cTheta->fill(cTheta);
  }
}


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

/// @}


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

};

RIVET_DECLARE_PLUGIN(BELLE_2005_I677084);

} ```