Rivet analyses

title: LHCB_2012_I1097092

$B_c^+\to J/\psi\pi^+$ and $B_c^+\to J/\psi\pi^+\pi^+\pi^-$

Experiment: LHCB (LHC)

Inspire ID: 1097092

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phy.Rev.Lett. 108 (2012) 251802

Beams: * *

Beam energies: ANY

Run details: - Any process producing B_c+, originally pp

Angular distributions in between the muons $B_c^+\to J/\psi\pi^+$ and $B_c^+\to J/\psi\pi^+\pi^+\pi^-$ with the muons from $J/\psi\to\mu^+\mu^-$ and mass distributions in $B_c^+\to J/\psi\pi^+\pi^+\pi^-$. The data were read from the plots in the paper and may not be corrected for efficiency and acceptance.

Source code:LHCB_2012_I1097092.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief B_c - > jpsi pi+ and pi+pi+pi- class LHCB_2012_I1097092 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(LHCB_2012_I1097092);


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

/// Book histograms and initialise projections before the run
void init() {
  UnstableParticles ufs = UnstableParticles(Cuts::abspid == 541);
  declare(ufs, "UFS");
  DecayedParticles BC(ufs);
  BC.addStable(PID::PI0);
  BC.addStable(PID::K0S);
  BC.addStable(PID::JPSI);
  declare(BC, "BC");
  for (unsigned int ix = 0; ix < 2; ++ix) {
    book(_h_mass[ix], 1 + ix, 1, 1);
    book(_h_ctheta[ix], 3, 1, 1 + ix);
  }
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  static const map<PdgId, unsigned int>& mode1 = {{443, 1}, {211, 1}};
  static const map<PdgId, unsigned int>& mode1CC = {{443, 1}, {-211, 1}};
  static const map<PdgId, unsigned int>& mode2 = {{443, 1}, {211, 2}, {-211, 1}};
  static const map<PdgId, unsigned int>& mode2CC = {{443, 1}, {-211, 2}, {211, 1}};
  DecayedParticles BC = apply<DecayedParticles>(event, "BC");
  // loop over particles
  for (unsigned int ix = 0; ix < BC.decaying().size(); ++ix) {
    int sign = BC.decaying()[ix].pid() / BC.decaying()[ix].abspid();
    int imode = -1;
    if ((sign == 1 && BC.modeMatches(ix, 2, mode1)) || (sign == -1 && BC.modeMatches(ix, 2, mode1CC))) {
      imode = 0;
    }
    else if ((sign == 1 && BC.modeMatches(ix, 4, mode2))
             || (sign == -1 && BC.modeMatches(ix, 4, mode2CC))) {
      const Particle& pim = BC.decayProducts()[ix].at(-sign * 211)[0];
      const Particles& pip = BC.decayProducts()[ix].at(sign * 211);
      _h_mass[0]->fill((pim.momentum() + pip[0].momentum() + pip[1].momentum()).mass());
      _h_mass[1]->fill((pim.momentum() + pip[0].momentum()).mass());
      _h_mass[1]->fill((pim.momentum() + pip[1].momentum()).mass());
      imode = 1;
    }
    else
      continue;
    // check the J/psi decay mode
    const Particle& jpsi = BC.decayProducts()[ix].at(443)[0];
    if (jpsi.children().size() != 2 || jpsi.children()[0].pid() != -jpsi.children()[1].pid()
        || jpsi.children()[0].abspid() != 13)
      continue;
    Particle muon = jpsi.children()[0].pid() == 13 ? jpsi.children()[0] : jpsi.children()[1];
    LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(
        BC.decaying()[ix].momentum().betaVec());
    FourMomentum pJPsi = boost1.transform(jpsi.momentum());
    FourMomentum pMu = boost1.transform(muon.momentum());
    // to j/psi rest frame
    LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pJPsi.betaVec());
    Vector3 axis = pJPsi.p3().unit();
    FourMomentum pp = boost2.transform(pMu);
    // calculate angle
    double cTheta = pp.p3().unit().dot(axis);
    _h_ctheta[imode]->fill(cTheta);
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  for (unsigned int ix = 0; ix < 2; ++ix) {
    normalize(_h_mass[ix]);
    normalize(_h_ctheta[ix]);
  }
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h_mass[2];
Histo1DPtr _h_ctheta[2];
/// @}

};

RIVET_DECLARE_PLUGIN(LHCB_2012_I1097092);

} ```