Rivet analyses

title: BELLE_2020_I1796822

$m_{\pi\pi}$ and $q^2$ distribution in $B^+\to\pi^+\pi^-\ell^+\nu_\ell$

Experiment: BELLE (KEKB)

Inspire ID: 1796822

Status: VALIDATED

Authors: - Peter Richardson

References: - arXiv: 2005.07766

Beams: * *

Beam energies: ANY

Run details: - Any process producing the relevant decay, originally e+e- at the Upsilon(4s)

Measurement of the $m_{\pi\pi}$ and $q^2$ distributions in the $B^+\to\pi^+\pi^-\ell^+\nu_\ell$ decay by the BELLE collaboration

Source code:BELLE_2020_I1796822.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief B->D semileptonic decays class BELLE_2020_I1796822 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2020_I1796822);


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

/// Book histograms and initialise projections before the run
void init() {

  // Initialise and register projections
  declare(UnstableParticles(), "UFS");
  // Book histograms
  book(_h_mpipi, 1, 1, 1);
  book(_h_q2, 2, 1, 1);
  book(_nB, "/TMP/nB");
}

void findChildren(const Particle& p, unsigned int& ncount, Particles& pi, Particles& ell, Particles& nu) {
  _nB->fill();
  for (const Particle& child : p.children()) {
    if (child.children().empty()) {
      if (child.abspid() == 211) {
        ++ncount;
        pi.push_back(child);
      }
      else if (child.abspid() == 11 || child.abspid() == 13) {
        ++ncount;
        ell.push_back(child);
      }
      else if (child.abspid() == 12 || child.abspid() == 14) {
        ++ncount;
        nu.push_back(child);
      }
      else if (child.pid() != 22)
        ++ncount;
    }
    // veto gamma gamma decaying mesons and K0
    else if (child.pid() == 111 || child.pid() == 221 || child.pid() == 331 || child.pid() == 130
             || child.pid() == 310) {
      ++ncount;
    }
    else
      findChildren(child, ncount, pi, ell, nu);
  }
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  for (const Particle& p : apply<UnstableParticles>(event, "UFS").particles(Cuts::pid == PID::BPLUS)) {
    Particles pi, ell, nu;
    unsigned int ncount = 0;
    findChildren(p, ncount, pi, ell, nu);
    // check the decay
    // 4 outgoing
    if (ncount != 4) continue;
    // including pi+ pi-
    if (pi.size() != 2 || pi[0].pid() != -pi[1].pid()) continue;
    // and ell- nubar or ell+ nu
    if (ell.size() != 1 || nu.size() != 1) continue;
    int inu = ell[0].abspid() + 1;
    if (ell[0].pid() > 0) inu *= -1;
    if (nu[0].pid() != inu) continue;
    // fill histos
    // m pipi
    FourMomentum ppi = pi[0].momentum() + pi[1].momentum();
    _h_mpipi->fill(ppi.mass());
    // q2
    FourMomentum q = p.momentum() - ppi;
    _h_q2->fill(q.mass2());
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  scale(_h_mpipi, 1e5 / *_nB);
  scale(_h_q2, 1e5 / *_nB);
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h_mpipi, _h_q2;
CounterPtr _nB;
/// @}

};

RIVET_DECLARE_PLUGIN(BELLE_2020_I1796822);

} ```