Rivet analyses

title: BELLE_2011_I889524

Mass and angular distributions in $B^0_S\to J\psi\pi^+\pi^-$

Experiment: BELLE (KEKB)

Inspire ID: 889524

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.Lett. 106 (2011) 121802

Beams: * *

Beam energies: ANY

Run details: - Any process producing B_s0, original Upsilon(5S) decay

THe $\pi^+\pi^-$ mass distribution and helcity angle distributions in the $f_0(980)$ and $f_0(1370)$ mass regions for the decay $B^0_S\to J\psi\pi^+\pi^-$ measured by BELLE

Source code:BELLE_2011_I889524.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief Bs0 -> pi+ pi- J/psi class BELLE_2011_I889524 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2011_I889524);


/// @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
  book(_h_mass, 1, 1, 1);
  for (unsigned int ix = 0; ix < 2; ++ix) book(_h_cTheta[ix], 2, 1, 1 + ix);
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  static const map<PdgId, unsigned int>& mode = {{211, 1}, {-211, 1}, {443, 1}};
  DecayedParticles BS0 = apply<DecayedParticles>(event, "BS0");
  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];
    double mpipi = (pip.momentum() + pim.momentum()).mass();
    _h_mass->fill(mpipi);
    // 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 boost1 = LorentzTransform::mkFrameTransformFromBeta(
        BS0.decaying()[ix].momentum().betaVec());
    FourMomentum ppsi = boost1.transform(JPsi.momentum());
    Vector3 axis1 = ppsi.p3().unit();
    LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(ppsi.betaVec());
    FourMomentum plp = boost2.transform(boost1.transform(lp.momentum()));
    double cTheta = plp.p3().unit().dot(axis1);
    if (mpipi > 0.8 && mpipi < 1.16)
      _h_cTheta[0]->fill(cTheta);
    else if (mpipi > 1.3 && mpipi < 1.5)
      _h_cTheta[1]->fill(cTheta);
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  normalize(_h_mass, 1., false);
  for (unsigned int ix = 0; ix < 2; ++ix) normalize(_h_cTheta[ix], 1., false);
}

/// @}


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

};

RIVET_DECLARE_PLUGIN(BELLE_2011_I889524);

} ```