Rivet analyses

title: BELLE_2004_I623994

Helicity angle in $B^+\to\psi(3770)K^+$

Experiment: BELLE (KEKB)

Inspire ID: 623994

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.Lett. 93 (2004) 051803

Beams: * *

Beam energies: ANY

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

Measurement of the helicity angle in $B^+\to\psi(3770)K^+$. The data were read from figure 3 in the paper.

Source code:BELLE_2004_I623994.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief B+ -> psi(3770) K+ class BELLE_2004_I623994 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2004_I623994);


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

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  UnstableParticles ufs = UnstableParticles(Cuts::abspid == 521);
  declare(ufs, "UFS");
  // histos
  book(_h, 1, 1, 1);
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  UnstableParticles ufs = apply<UnstableParticles>(event, "UFS");
  for (const Particle& B : ufs.particles()) {
    if (B.children().size() != 2) continue;
    int sign = B.pid() / B.abspid();
    // boost to B rest frame
    LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(B.mom().betaVec());
    Particle resonance;
    if (B.children()[0].pid() == 30443 && B.children()[1].pid() == sign * 321) {
      resonance = B.children()[0];
    }
    else if (B.children()[1].pid() == 30443 && B.children()[0].pid() == sign * 321) {
      resonance = B.children()[1];
    }
    else {
      continue;
    }
    if (resonance.children().size() != 2) continue;
    FourMomentum pRes = boost1.transform(resonance.mom());
    LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pRes.betaVec());
    Vector3 axis1 = pRes.p3().unit();
    Particle child;
    if (resonance.children()[0].pid() != -resonance.children()[1].pid()) continue;
    if (resonance.children()[0].abspid() != 411 && resonance.children()[0].abspid() != 421) continue;
    child = resonance.children()[0].pid() > 0 ? resonance.children()[0] : resonance.children()[1];
    Vector3 axis2 = boost2.transform(boost1.transform(child.mom())).p3().unit();
    _h->fill(axis1.dot(axis2));
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  normalize(_h, 1.0, false);
}

/// @}


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

};

RIVET_DECLARE_PLUGIN(BELLE_2004_I623994);

} ```