Rivet analyses

title: BABAR_2009_I821188

Mass distributions in $B^0\to K^0_S\pi^+\pi^-$ decays

Experiment: BABAR (PEP-II)

Inspire ID: 821188

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 80 (2009) 112001

Beams: * *

Beam energies: ANY

Run details: - Any process producing B0, originally Upsilon(4S) decay

Measurement of mass distributions in $B^0\to K^0_S\pi^+\pi^-$ decays. The data were read from the plots in the paper and may not be corrected for efficiency/acceptance, however the backgrounds shown in the paper have been subtracted.

Source code:BABAR_2009_I821188.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief B0 > KS0 pi+ pi- class BABAR_2009_I821188 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2009_I821188);


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

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  UnstableParticles ufs = UnstableParticles(Cuts::abspid == 511);
  declare(ufs, "UFS");
  DecayedParticles B0(ufs);
  B0.addStable(PID::K0S);
  declare(B0, "B0");
  // histograms
  for (unsigned int ix = 0; ix < 2; ++ix)
    for (unsigned int iy = 0; iy < 2; ++iy) book(_h[ix][iy], 1 + ix, 1, 1 + iy);
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  static const map<PdgId, unsigned int>& mode = {{310, 1}, {211, 1}, {-211, 1}};
  DecayedParticles B0 = apply<DecayedParticles>(event, "B0");
  // loop over particles
  for (unsigned int ix = 0; ix < B0.decaying().size(); ++ix) {
    if (!B0.modeMatches(ix, 3, mode)) continue;
    int sign = B0.decaying()[ix].pid() > 0 ? 1 : -1;
    // boost to B rest frame
    LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(
        B0.decaying()[ix].momentum().betaVec());
    // momenta
    FourMomentum pip = boost.transform(B0.decayProducts()[ix].at(211 * sign)[0].momentum());
    FourMomentum pim = boost.transform(B0.decayProducts()[ix].at(-211 * sign)[0].momentum());
    FourMomentum K0 = boost.transform(B0.decayProducts()[ix].at(310)[0].momentum());
    // pi+pi- resonance
    FourMomentum ppipi = pim + pip;
    LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(ppipi.betaVec());
    double cTheta = boost2.transform(pim).p3().unit().dot(K0.p3().unit());
    if (cTheta > 0.)
      _h[0][0]->fill(ppipi.mass());
    else
      _h[0][1]->fill(ppipi.mass());
    // K pi- resonance
    FourMomentum pKpim = K0 + pim;
    boost2 = LorentzTransform::mkFrameTransformFromBeta(pKpim.betaVec());
    cTheta = boost2.transform(K0).p3().unit().dot(pip.p3().unit());
    if (cTheta > 0.)
      _h[1][0]->fill(pKpim.mass());
    else
      _h[1][1]->fill(pKpim.mass());
    // K pi+ resonance
    FourMomentum pKpip = K0 + pip;
    boost2 = LorentzTransform::mkFrameTransformFromBeta(pKpip.betaVec());
    cTheta = boost2.transform(pip).p3().unit().dot(pim.p3().unit());
    if (cTheta > 0.)
      _h[1][0]->fill(pKpip.mass());
    else
      _h[1][1]->fill(pKpip.mass());
  }
}


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

/// @}


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

};

RIVET_DECLARE_PLUGIN(BABAR_2009_I821188);

} ```