Rivet analyses

Helicity angles in B → D̄Ds1+(2536), B → ψ(3770)K and B → X(3872)K

Experiment: BABAR (PEP-II)

Inspire ID: 758167

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 77 (2008) 011102

Beams: * *

Beam energies: ANY

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

Measurement of helicity angles in B → D̄Ds1+(2536), B → ψ(3770)K and B → X(3872)K decays using B → D̄(*)D(*)K modes. The background subtracted, efficiency corrected distributions were read from Figure 1 in the paper. There is no consensus as to the nature of the X(3872) cc̄ state and therefore we taken its PDG code to be 9030443, i.e. the first unused code for an undetermined spin one cc̄ state. This can be changed using the PID option if a different code is used by the event generator performing the simulation.

Source code:BABAR_2008_I758167.cc

// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {


  /// @brief B -> D(*) D(*) K
  class BABAR_2008_I758167 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2008_I758167);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // set the PDG code
      _pid = getOption<int>("PID", 9030443);
      // Initialise and register projections
      UnstableParticles ufs = UnstableParticles(Cuts::abspid == 511 || Cuts::abspid == 521);
      declare(ufs, "UFS");
      // histos
      for (unsigned int ix = 0; ix < 3; ++ix) book(_h[ix], 1, 1, 1 + ix);
    }

    bool isK(int id) {
      return id == 321 || id == 311 || id == 310 || id == 130;
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      UnstableParticles ufs = apply<UnstableParticles>(event, "UFS");
      for (const Particle& B : ufs.particles()) {
        if (B.children().size() != 2) continue;
        int sign = B.pid() / B.abspid(), iD = B.abspid() - 100;
        unsigned int imode = 0;
        // boost to B rest frame
        LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(B.momentum().betaVec());
        Particle resonance;
        if (B.children()[0].pid() == sign * 10433 && B.children()[1].pid() == -sign * iD) {
          imode = 0;
          resonance = B.children()[0];
        }
        else if (B.children()[1].pid() == sign * 10433 && B.children()[0].pid() == -sign * iD) {
          imode = 0;
          resonance = B.children()[1];
        }
        else if (B.children()[0].pid() == 30443 && isK(B.children()[1].pid())) {
          imode = 1;
          resonance = B.children()[0];
        }
        else if (B.children()[1].pid() == 30443 && isK(B.children()[0].pid())) {
          imode = 1;
          resonance = B.children()[1];
        }
        else if (B.children()[0].pid() == _pid && isK(B.children()[1].pid())) {
          imode = 2;
          resonance = B.children()[0];
        }
        else if (B.children()[1].pid() == _pid && isK(B.children()[0].pid())) {
          imode = 2;
          resonance = B.children()[1];
        }
        else
          continue;
        if (resonance.children().size() != 2) continue;
        FourMomentum pRes = boost1.transform(resonance.momentum());
        LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pRes.betaVec());
        Vector3 axis1 = -pRes.p3().unit();
        Particle child;
        if (imode == 0) {
          Particle Dstar;
          if (isK(resonance.children()[1].pid())
              && (resonance.children()[0].pid() == sign * 413 || resonance.children()[0].pid() == sign * 423))
            child = resonance.children()[0];
          else if (isK(resonance.children()[0].pid())
                   && (resonance.children()[1].pid() == sign * 413
                       || resonance.children()[1].pid() == sign * 423))
            child = resonance.children()[1];
          else
            continue;
        }
        // B -> D psi(3770)
        else if (imode == 1) {
          if (resonance.children()[0].pid() != -resonance.children()[1].pid()) continue;
          if (resonance.children()[0].abspid() != 411 && resonance.children()[0].abspid() != 421) continue;
          child = resonance.children()[0].pid() > 0 ? resonance.children()[0] : resonance.children()[1];
        }
        else if (imode == 2) {
          if ((resonance.children()[0].abspid() == 423 && resonance.children()[1].abspid() == 421)
              || (resonance.children()[1].abspid() == 423 && resonance.children()[0].abspid() == 421)) {
            child = resonance.children()[0].pid() > 0 ? resonance.children()[0] : resonance.children()[1];
          }
          else
            continue;
        }
        Vector3 axis2 = boost2.transform(boost1.transform(child.momentum())).p3().unit();
        _h[imode]->fill(axis1.dot(axis2));
      }
    }


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

    /// @}


    /// @name Histograms
    /// @{
    int _pid;
    Histo1DPtr _h[3];
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BABAR_2008_I758167);

}