Rivet analyses

title: LHCB_2013_I1081268

Helicity angles in $B^0_S\to J/\psi f_0(980)$

Experiment: LHCB (LHC)

Inspire ID: 1081268

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Lett.B 707 (2012) 497-505

Beams: * *

Beam energies: ANY

Run details: - Any process producing B_s0, originally pp

Measurement of the helicity angles in $B^0_S\to J/\psi f_0(980)$. The corrected data were read from Figure 4 in the paper.

Source code:LHCB_2013_I1081268.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief BS0 -> J/psi f0 class LHCB_2013_I1081268 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(LHCB_2013_I1081268);


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

/// Book histograms and initialise projections before the run
void init() {
  // projections
  UnstableParticles ufs = UnstableParticles(Cuts::abspid == 531);
  declare(ufs, "UFS");
  DecayedParticles BS0(ufs);
  BS0.addStable(443);
  declare(BS0, "BS0");
  // histograms
  for (unsigned int ix = 0; ix < 2; ++ix) {
    book(_h[ix], 1, 1, 1 + ix);
  }
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  DecayedParticles BS0 = apply<DecayedParticles>(event, "BS0");
  static const map<PdgId, unsigned int> mode = {{211, 1}, {-211, 1}, {443, 1}};
  for (unsigned int ix = 0; ix < BS0.decaying().size(); ++ix) {
    if (!BS0.modeMatches(ix, 3, mode)) continue;
    const Particle& pip = BS0.decayProducts()[ix].at(211)[0];
    const Particle& pim = BS0.decayProducts()[ix].at(-211)[0];
    const Particle& JPsi = BS0.decayProducts()[ix].at(443)[0];
    FourMomentum ppipi = pip.mom() + pim.mom();
    // mass cut and presence of f_0(980)
    const double mpipi = ppipi.mass();
    if (abs(mpipi - 0.98) > 0.9) continue;
    if (count(BS0.decaying()[ix].children(), hasPID(9010221)) != 1) continue;
    // f_0 helicity angle
    LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(
        BS0.decaying()[ix].mom().betaVec());
    FourMomentum ppsi = boost1.transform(JPsi.mom());
    Vector3 axis1 = ppsi.p3().unit();
    ppipi = boost1.transform(ppipi);
    LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(ppipi.betaVec());
    FourMomentum ppip = boost2.transform(boost1.transform(pip.mom()));
    _h[1]->fill(ppip.p3().unit().dot(axis1));
    // helicity angle find J.psi leptonic children
    if (JPsi.children().size() != 2) continue;
    if (JPsi.children()[0].pid() != -JPsi.children()[1].pid()) continue;
    if (JPsi.children()[0].abspid() != PID::EMINUS && JPsi.children()[0].abspid() != PID::MUON) continue;
    Particle lm = JPsi.children()[0];
    Particle lp = JPsi.children()[1];
    if (lm.pid() < 0) swap(lm, lp);
    LorentzTransform boost3 = LorentzTransform::mkFrameTransformFromBeta(ppsi.betaVec());
    FourMomentum plp = boost3.transform(boost1.transform(lp.mom()));
    _h[0]->fill(-plp.p3().unit().dot(axis1));
  }
}


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

/// @}


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

};

RIVET_DECLARE_PLUGIN(LHCB_2013_I1081268);

} ```