Rivet analyses

Measurement of the mass mX produced in B → η′Xs

Experiment: BABAR (PEP-II)

Inspire ID: 642355

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Rev.Lett. 93 (2004) 061801

Beams: * *

Beam energies: ANY

Run details: - Any process producing Upsilon(4S), originally e+e-

Measurement of the mass mX produced in B → η′Xs where the η′ meson has momentum 2 < p < 2.7 GeV in the Υ(4S) rest frame.

Source code:BABAR_2004_I642355.cc

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

namespace Rivet {


  /// @brief M_x in B -> eta' Xs
  class BABAR_2004_I642355 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2004_I642355);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // projections
      declare(UnstableParticles(), "UFS");
      // histograms
      book(_w_ups4, "/TMP/w_ups4");
      book(_h_X, 1, 1, 1);
    }

    void findDecay(Particle parent,
                   bool& charm,
                   Particles& etaP,
                   Particles& pi0,
                   Particles& pip,
                   Particles& Kp,
                   Particles& K0) {
      for (const Particle& p : parent.children()) {
        if (isCharm(p)) {
          charm = true;
          return;
        }
        else if (p.pid() == PID::ETAPRIME) {
          etaP.push_back(p);
        }
        else if (p.abspid() == PID::PIPLUS) {
          pip.push_back(p);
        }
        else if (p.abspid() == PID::KPLUS) {
          Kp.push_back(p);
        }
        else if (p.pid() == PID::PI0) {
          pi0.push_back(p);
        }
        else if (p.pid() == PID::K0S) {
          K0.push_back(p);
        }
        else if (!p.children().empty()) {
          findDecay(p, charm, etaP, pi0, pip, Kp, K0);
        }
      }
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      const UnstableParticles& ufs = apply<UnstableParticles>(event, "UFS");
      for (const Particle& p : ufs.particles(Cuts::pid == 300553)) {
        _w_ups4->fill();
        const LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(p.mom().betaVec());
        for (const Particle& B : p.children()) {
          if (B.abspid() != 511 && B.abspid() != 521) continue;
          // find the decay
          bool charm = false;
          Particles etaP, pi0, pip, Kp, K0;
          findDecay(B, charm, etaP, pi0, pip, Kp, K0);
          if (charm || etaP.size() != 1) continue;
          if (Kp.empty() && Kp.empty()) continue;
          double pEta = boost.transform(etaP[0].momentum()).p3().mod();
          if (pEta < 2. || pEta > 2.7) continue;
          // four momentum of the Xs system
          FourMomentum pX;
          if (K0.size() == 1)
            pX += K0[0].momentum();
          else if (Kp.size() == 1)
            pX += Kp[0].momentum();
          else
            continue;
          for (const Particle& pi : pip) pX += pi.momentum();
          if (pi0.size() == 1) pX += pi0[0].momentum();
          _h_X->fill(pX.mass());
        }
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      scale(_h_X, 0.5 / *_w_ups4);
    }

    /// @}


    /// @name Histograms
    /// @{
    CounterPtr _w_ups4;
    Histo1DPtr _h_X;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BABAR_2004_I642355);

}