Rivet analyses

title: BELLE_2017_I1499706

$\chi_{c1}$ spectrum in $\Upsilon(1,2S)$ decays

Experiment: BELLE (KEKB)

Inspire ID: 1499706

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 95 (2017) 1, 012001

Beams: * *

Beam energies: ANY

Run details: - Any process producing Upsilon(1S) or Upsilon(2S) originally e+e-

Measurement of the scaled momentum of $\chi_{c1}$ in $\Upsilon(1S)$ and $\Upsilon(2S)$ decays

Source code:BELLE_2017_I1499706.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief chi_c1 in Upsilon(1,2S) decays class BELLE_2017_I1499706 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2017_I1499706);


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

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  declare(UnstableParticles(Cuts::pid == 553 || Cuts::pid == 100553), "UFS");
  //histos
  for (unsigned int ix = 0; ix < 2; ++ix) {
    for (unsigned int iy = 0; iy < 2; ++iy) book(_h[ix][iy], 1, 1 + ix, 1 + iy);
    book(_c[ix], "TMP/nUps" + toString(ix + 1));
  }
}

/// Recursively walk the decay tree to find decay products of @a p
void findDecayProducts(Particle mother, Particles& unstable) {
  for (const Particle& p : mother.children()) {
    const int id = abs(p.pid());
    if (id == 20443) {
      unstable.push_back(p);
    }
    if (!p.children().empty()) findDecayProducts(p, unstable);
  }
}

/// Perform the per-event analysis
void analyze(const Event& event) {
  // Find the Upsilons among the unstables
  for (const Particle& ups : apply<UnstableParticles>(event, "UFS").particles()) {
    unsigned int iloc = ups.pid() / 100000;
    _c[iloc]->fill();
    // boost to rest frame
    LorentzTransform boost;
    if (ups.p3().mod() > 1 * MeV)
      boost = LorentzTransform::mkFrameTransformFromBeta(ups.momentum().betaVec());
    // find ch_c1
    Particles unstable;
    findDecayProducts(ups, unstable);
    // loop over chi_c1
    for (const Particle& chi : unstable) {
      double Pmax = 0.5 * (sqr(ups.mass()) - sqr(chi.mass())) / ups.mass();
      const FourMomentum p2 = boost.transform(chi.momentum());
      const double xP = p2.p3().mod() / Pmax;
      _h[0][iloc]->fill(xP);
      _h[1][iloc]->fill(xP);
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  for (unsigned int ix = 0; ix < 2; ++ix)
    for (unsigned int iy = 0; iy < 2; ++iy) scale(_h[ix][iy], 1e4 / *_c[iy]);
}

/// @}


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

};

RIVET_DECLARE_PLUGIN(BELLE_2017_I1499706);

} ```