Rivet analyses

title: BABAR_2004_I642355

Measurement of the mass $m_X$ produced in $B\to\eta^\prime X_s$

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 $m_X$ produced in $B\to\eta^\prime X_s$ where the $\eta^\prime$ meson has momentum $2<p<2.7$ GeV in the $\Upsilon(4S)$ rest frame.

Source code:BABAR_2004_I642355.cc

```c++ // -- 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);

} ```