Rivet analyses

Helicity angles in BS0 → J/ψf0(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 BS0 → J/ψf0(980). The corrected data were read from Figure 4 in the paper.

Source code:LHCB_2013_I1081268.cc

// -*- 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);

}