Rivet analyses

title: LHCB_2015_I1327230

$B_c^+$ meson production at 8 TeV

Experiment: LHCB (LHC)

Inspire ID: 1327230

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Rev.Lett. 114 (2015) 132001

Beams: p+ p+

Beam energies: (4000.0, 4000.0)GeV

Run details: - hadronic events with B meson

Measurement of the double differential (in $p_\perp$ and $y$) ratio $B_c^+/B^+$ meson production at 8 TeV by the LHCb collaboration. The branching ratio for the decay $B^+\to J\psi K^+$ is taken to be $0.00102$ from PDG2023 while by default the branching ratio for $B_c^+\to J\psi\pi^+$ is measured from the events, however it can be specified using the BCBR option.

Source code:LHCB_2015_I1327230.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief B_c production class LHCB_2015_I1327230 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(LHCB_2015_I1327230);


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

/// Book histograms and initialise projections before the run
void init() {
  declare(UnstableParticles(), "UFS");
  for (unsigned int ib = 0; ib < 2; ++ib) {
    book(_h_pT[ib], "TMP/h_pT_" + toString(ib), refData(2, 1, 1));
    book(_h_y[ib], "TMP/h_y_" + toString(ib), refData(3, 1, 1));
    book(_h_B[ib], {2.0, 2.9, 3.3, 4.5});
    for (unsigned int iy = 0; iy < 3; ++iy) {
      book(_h_B[ib]->bin(iy + 1), "TMP/hB_" + toString(ib) + "_" + toString(iy), refData(1, 1, 1 + iy));
    }
    book(_c_Bc[ib], "TMP/c_Bc_" + toString(ib));
  }
  _brBp = getOption<double>("BPBR", 1.02e-3);
  _brBc = getOption<double>("BCBR", -1.);
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  // Final state of unstable particles to get particle spectra
  const UnstableParticles& ufs = apply<UnstableParticles>(event, "UFS");
  for (const Particle& p : ufs.particles(Cuts::pid == 521 or Cuts::pid == 541)) {
    if (p.pid() == 541) {
      if (p.children().size() == 2
          && ((p.children()[0].pid() == 211 && p.children()[1].pid() == 443)
              || (p.children()[1].pid() == 211 && p.children()[0].pid() == 443)))
        _c_Bc[0]->fill(1.);
      _c_Bc[1]->fill(1.);
    }
    double absrap = p.absrap();
    if (absrap < 2. || absrap > 4.5) continue;
    double pT = p.perp();
    // select B0
    if (p.pid() == 521) {
      _h_B[1]->fill(absrap, pT);
      _h_pT[1]->fill(pT);
      if (pT < 20.) _h_y[1]->fill(absrap);
    }
    // select B_c+
    else {
      _h_B[0]->fill(absrap, pT);
      _h_pT[0]->fill(pT);
      if (pT < 20.) _h_y[0]->fill(absrap);
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  // branching ratio Bc -> J/psi pi+
  if (_brBc < 0.) {
    Estimate0DPtr tmp2;
    book(tmp2, "TMP/br");
    divide(_c_Bc[0], _c_Bc[1], tmp2);
    _brBc = tmp2->val();
  }
  // scale by B+ br (for B_c directly selected before filling histos)
  scale(_h_B[0], _brBc);
  scale(_h_B[1], _brBp);
  for (unsigned int ix = 0; ix < 2; ++ix) divByGroupWidth(_h_B[ix]);
  scale(_h_pT[0], _brBc);
  scale(_h_pT[1], _brBp);
  scale(_h_y[0], _brBc);
  scale(_h_y[1], _brBp);
  for (unsigned int iy = 0; iy < 3; ++iy) {
    Estimate1DPtr tmp;
    book(tmp, 1, 1, 1 + iy);
    divide(_h_B[0]->bin(iy + 1), _h_B[1]->bin(iy + 1), tmp);
    // convert ratio to %
    tmp->scale(100.);
  }
  Estimate1DPtr tmp;
  book(tmp, 2, 1, 1);
  divide(_h_pT[0], _h_pT[1], tmp);
  // convert ratio to %
  tmp->scale(100.);
  book(tmp, 3, 1, 1);
  divide(_h_y[0], _h_y[1], tmp);
  // convert ratio to %
  tmp->scale(100.);
}

/// @}


/// @name Histograms
/// @{
Histo1DGroupPtr _h_B[2];
Histo1DPtr _h_pT[2], _h_y[2];
CounterPtr _c_Bc[2];
double _brBp, _brBc;
/// @}

};

RIVET_DECLARE_PLUGIN(LHCB_2015_I1327230);

} ```