Rivet analyses

title: BABAR_2009_I810694

Mass distributions in $B^-\to D^+\pi^-\pi^-$

Experiment: BABAR (PEP-II)

Inspire ID: 810694

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 79 (2009) 112004

Beams: * *

Beam energies: ANY

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

Measurement of mass and angular distributions in $B^-\to D^+\pi^-\pi^-$. The data were read from the plots in the paper and may not be corrected for acceptance/efficiency, however the backgrounds given in the paper were subtracted.

Source code:BABAR_2009_I810694.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief B- > D+ pi-pi- class BABAR_2009_I810694 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2009_I810694);


/// @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(411);
  BP.addStable(-411);
  declare(BP, "BP");
  // histograms
  for (unsigned int ix = 0; ix < 3; ++ix) {
    if (ix < 2) book(_h_angle[ix], 2, 1, 1 + ix);
    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 = {{-411, 1}, {211, 2}};
  static const map<PdgId, unsigned int>& modeCC = {{411, 1}, {-211, 2}};
  DecayedParticles BP = apply<DecayedParticles>(event, "BP");
  // loop over particles
  for (unsigned int ix = 0; ix < BP.decaying().size(); ++ix) {
    int sign = 1;
    if (BP.modeMatches(ix, 3, mode))
      sign = 1;
    else if (BP.modeMatches(ix, 3, modeCC))
      sign = -1;
    else
      continue;
    const Particle& Dp = BP.decayProducts()[ix].at(-sign * 411)[0];
    const Particles& pim = BP.decayProducts()[ix].at(sign * 211);
    _h_mass[2]->fill((pim[0].momentum() + pim[1].momentum()).mass2());
    // boost to B rest frame
    LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(
        BP.decaying()[ix].momentum().betaVec());
    FourMomentum pD = boost.transform(Dp.momentum());
    FourMomentum ppi[2] = {boost.transform(pim[0].momentum()), boost.transform(pim[1].momentum())};
    double m2Dpi[2];
    for (unsigned int ix = 0; ix < 2; ++ix) {
      m2Dpi[ix] = (pim[ix].momentum() + Dp.momentum()).mass2();
      if ((m2Dpi[ix] > 4.5 && m2Dpi[ix] < 5.5) || (m2Dpi[ix] > 5.9 && m2Dpi[ix] < 6.2)) {
        FourMomentum pDpi = pD + pim[ix];
        LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pDpi.betaVec());
        Vector3 axis1 = boost2.transform(ppi[ix]).p3().unit();
        Vector3 axis2 = (ix == 0 ? ppi[1] : ppi[0]).p3().unit();
        double cTheta = axis1.dot(axis2);
        if (m2Dpi[ix] < 5.5)
          _h_angle[0]->fill(cTheta);
        else
          _h_angle[1]->fill(cTheta);
      }
    }
    if (m2Dpi[0] > m2Dpi[1]) {
      _h_mass[1]->fill(m2Dpi[0]);
      _h_mass[0]->fill(m2Dpi[1]);
    }
    else {
      _h_mass[0]->fill(m2Dpi[0]);
      _h_mass[1]->fill(m2Dpi[1]);
    }
  }
}


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

/// @}


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

};

RIVET_DECLARE_PLUGIN(BABAR_2009_I810694);

} ```