Rivet analyses

title: BABAR_2004_I632399

$\phi$ momentum spectra in $\Upsilon(4S)$ decays

Experiment: BABAR (PEP-II)

Inspire ID: 632399

Status: VALIDATED

Authors: - Peter Richardson

References: none listed

Beams: * *

Beam energies: ANY

Run details: - Any process producing Upsilon(4S) originally e+e-

Measurement of the momentum spectrum of $\phi$ mesons produced in $B$ decays at the $\Upsilon(4S)$ resonance.

Source code:BABAR_2004_I632399.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief phi spectrum at 4S class BABAR_2004_I632399 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2004_I632399);


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

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

  // Initialise and register projections
  declare(UnstableParticles(), "UFS");

  // Book histograms
  book(_b_phi, 1, 1, 1);
  book(_h_phi, 2, 1, 1);
  book(_c_4S, "/TMP/N4S");
}

void findDecayProducts(const Particle& p, Particles& phi) {
  for (const Particle& child : p.children()) {
    if (child.pid() == 333)
      phi.push_back(child);
    else if (!child.children().empty())
      findDecayProducts(child, phi);
  }
}

/// Perform the per-event analysis
void analyze(const Event& event) {
  // Find the Upsilons among the unstables
  const UnstableParticles& ufs = apply<UnstableParticles>(event, "UFS");
  Particles upsilons = ufs.particles(Cuts::pid == 300553);
  for (const Particle& ups : upsilons) {
    LorentzTransform cms_boost;
    if (ups.p3().mod() > 1 * MeV)
      cms_boost = LorentzTransform::mkFrameTransformFromBeta(ups.momentum().betaVec());
    Particles phis;
    findDecayProducts(ups, phis);
    _c_4S->fill();

    for (const Particle& phi : phis) {
      FourMomentum p2 = cms_boost.transform(phi.momentum());
      _h_phi->fill(p2.p3().mod());
      _b_phi->fill();
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  if (_c_4S->effNumEntries() != 0) {
    scale(_h_phi, 0.5 / *_c_4S);
    scale(_b_phi, 50. / *_c_4S);
  }
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h_phi;
CounterPtr _b_phi, _c_4S;
/// @}

};

RIVET_DECLARE_PLUGIN(BABAR_2004_I632399);

} ```