Rivet analyses

title: BABAR_2004_I626730

Mass and helicity angles in $B^+\to K^+\pi^+\pi^-$

Experiment: BABAR (PEP-II)

Inspire ID: 626730

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 70 (2004) 092001

Beams: * *

Beam energies: ANY

Run details: - Any process producing B+ mesons, originally Upsilon(4S) decays

Measurement of mass distributions and helicity angles in $B^+\to K^+\pi^+\pi^-$. The efficiency corrected, background subtracted data were read from the figures in the paper

Source code:BABAR_2004_I626730.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief B -> K pi pi class BABAR_2004_I626730 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2004_I626730);


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

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  UnstableParticles ufs = UnstableParticles(Cuts::abspid == 521);
  declare(ufs, "UFS");
  DecayedParticles BP(ufs);
  BP.addStable(PID::K0S);
  declare(BP, "BP");
  for (unsigned int ix = 0; ix < 3; ++ix) {
    book(_h_mass2[ix], 2, 1, 1 + ix);
    book(_h_angle[ix], 2, 2, 1 + ix);
    if (ix == 2) continue;
    book(_h_mass[ix], 1, 1, 1 + ix);
  }
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  static const map<PdgId, unsigned int>& mode = {{321, 1}, {211, 1}, {-211, 1}};
  static const map<PdgId, unsigned int>& modeCC = {{-321, 1}, {211, 1}, {-211, 1}};
  DecayedParticles BP = apply<DecayedParticles>(event, "BP");
  // loop over particles
  for (unsigned int ix = 0; ix < BP.decaying().size(); ++ix) {
    int sign = BP.decaying()[ix].pid() > 0 ? 1 : -1;
    if ((sign > 0 and BP.modeMatches(ix, 3, mode)) || (sign < 0 and BP.modeMatches(ix, 3, mode))) {
      // boost to B rest frame
      LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(
          BP.decaying()[ix].momentum().betaVec());
      // momenta
      FourMomentum pip = boost.transform(BP.decayProducts()[ix].at(211 * sign)[0].momentum());
      FourMomentum pim = boost.transform(BP.decayProducts()[ix].at(-211 * sign)[0].momentum());
      FourMomentum Kp = boost.transform(BP.decayProducts()[ix].at(321 * sign)[0].momentum());
      // mass distributions
      double mKpi = (Kp + pim).mass();
      _h_mass[0]->fill(mKpi);
      double mpipi = (pip + pim).mass();
      _h_mass[1]->fill(mpipi);
      // regions for the helicity analysis
      unsigned int imode = 0;
      if (mKpi > 0.816 && mKpi < 0.976 && mpipi > 1.5)
        imode = 0;
      else if (mpipi > 0.9 && mpipi < 1.1)
        imode = 1;
      else if (mKpi > 0.976 && mKpi < 1.8 && mpipi > 1.5)
        imode = 2;
      else
        continue;
      // pi+pi- resonance
      if (imode == 1) {
        _h_mass2[imode]->fill(mpipi);
        FourMomentum ppipi = pim + pip;
        LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(ppipi.betaVec());
        double cTheta = boost2.transform(pim).p3().unit().dot(Kp.p3().unit());
        _h_angle[imode]->fill(cTheta);
      }
      // K pi- resonance
      else {
        _h_mass2[imode]->fill(mKpi);
        FourMomentum pKpim = Kp + pim;
        LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pKpim.betaVec());
        double cTheta = boost2.transform(Kp).p3().unit().dot(pip.p3().unit());
        _h_angle[imode]->fill(cTheta);
      }
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  for (unsigned int ix = 0; ix < 3; ++ix) {
    normalize(_h_mass2[ix], 1., false);
    normalize(_h_angle[ix], 1., false);
    if (ix == 2) continue;
    normalize(_h_mass[ix], 1., false);
  }
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h_mass[2], _h_mass2[3], _h_angle[3];
/// @}

};

RIVET_DECLARE_PLUGIN(BABAR_2004_I626730);

} ```