Rivet analyses

title: BELLE_2002_I589587

$\pi\pi$ mass and helicity angle for $B^0\to\rho^\pm\pi^\mp$ and $B^+\to\rho^0\pi^+$

Experiment: BELLE (KEKB)

Inspire ID: 589587

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Lett.B 542 (2002) 183-192

Beams: * *

Beam energies: ANY

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

Measurement of the $\pi\pi$ mass and helicity angle for $B^0\to\rho^\pm\pi^\mp$ and $B^+\to\rho^0\pi^+$. The background subtracted data were read from figures 2 and 3 in the paper.

Source code:BELLE_2002_I589587.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief B -> rho pi class BELLE_2002_I589587 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2002_I589587);


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

/// Book histograms and initialise projections before the run
void init() {
  // projections
  UnstableParticles ufs = UnstableParticles(Cuts::abspid == 511 || Cuts::abspid == 521);
  declare(ufs, "UFS");
  DecayedParticles BB(ufs);
  BB.addStable(111);
  declare(BB, "BB");
  // histos
  for (unsigned int ix = 0; ix < 2; ++ix) {
    book(_h_mass[ix], 1, 1, 1 + ix);
    book(_h_angle[ix], 2, 1, 1 + ix);
  }
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  DecayedParticles BB = apply<DecayedParticles>(event, "BB");
  for (unsigned int ix = 0; ix < BB.decaying().size(); ++ix) {
    int sign = BB.decaying()[ix].pid() / BB.decaying()[ix].abspid();
    unsigned int imode = 0;
    if (BB.modeMatches(ix, 3, mode1))
      imode = 0;
    else if (sign == 1 && BB.modeMatches(ix, 3, mode2))
      imode = 1;
    else if (sign == -1 && BB.modeMatches(ix, 3, mode2CC))
      imode = 1;
    else
      continue;
    const Particles& pip = BB.decayProducts()[ix].at(sign * 211);
    const Particles& pim = BB.decayProducts()[ix].at(-sign * 211);
    bool pipiVeto = false;
    Particle pRho[2];
    double delta = 1e30;
    for (const Particle& p1 : pip) {
      for (const Particle& p2 : pim) {
        double mpipi = (p1.mom() + p2.mom()).mass();
        if (abs(mpipi - 1.86484) < 0.14 || abs(mpipi - 3.09690) < 0.07 || abs(mpipi - 3.68610) < 0.05) {
          pipiVeto = true;
          break;
        }
        if (abs(mpipi - .77) < delta) {
          delta = abs(mpipi - .77);
          pRho[0] = p1;
          pRho[1] = p2;
        }
      }
    }
    if (pipiVeto) continue;
    if (imode == 0) {
      const Particle& pi0 = BB.decayProducts()[ix].at(111)[0];
      delta = 1e30;
      for (const Particle& p1 : pip) {
        double mpipi = (p1.mom() + pi0.mom()).mass();
        if (abs(mpipi - 1.86966) < 0.05) {
          pipiVeto = true;
          break;
        }
        if (abs(mpipi - .77) < delta) {
          delta = abs(mpipi - .77);
          pRho[0] = p1;
          pRho[1] = pi0;
        }
      }
      if (pipiVeto) continue;
      for (const Particle& p1 : pim) {
        double mpipi = (p1.mom() + pi0.mom()).mass();
        if (abs(mpipi - 1.86966) < 0.05) {
          pipiVeto = true;
          break;
        }
        if (abs(mpipi - .77) < delta) {
          delta = abs(mpipi - .77);
          pRho[0] = p1;
          pRho[1] = pi0;
        }
      }
      if (pipiVeto) continue;
    }
    FourMomentum prho = pRho[0].mom() + pRho[1].mom();
    double mpipi = prho.mass();
    _h_mass[imode]->fill(mpipi);
    // check if we should compute helicty angle
    if (imode == 0 && (mpipi < .6 || mpipi > 0.95))
      continue;
    else if (imode == 1 && (mpipi < .62 || mpipi > 0.92))
      continue;
    // compute the helicity angle
    LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(
        BB.decaying()[ix].mom().betaVec());
    prho = boost1.transform(prho);
    FourMomentum ppi = boost1.transform(pRho[0].mom());
    LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(prho.betaVec());
    ppi = boost2.transform(ppi);
    double cTheta = ppi.p3().unit().dot(prho.p3().unit());
    _h_angle[imode]->fill(cTheta);
  }
}


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

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h_mass[2], _h_angle[2];
const map<PdgId, unsigned int> mode1 = {{211, 1}, {-211, 1}, {111, 1}};
const map<PdgId, unsigned int> mode2 = {{211, 2}, {-211, 1}};
const map<PdgId, unsigned int> mode2CC = {{-211, 2}, {211, 1}};
/// @}

};

RIVET_DECLARE_PLUGIN(BELLE_2002_I589587);

} ```