Rivet analyses

title: ALEPH_2014_I1267648

Normalised spectral functions of hadronic tau decays

Experiment: ALEPH (LEP)

Inspire ID: 1267648

Status: VALIDATED

Authors: - Holger Schulz

References: none listed

Beams: * *

Beam energies: ANY

Run details: - Hadronic tau decays.

Spectral functions of pionic tau decays measured with ALEPH. The data is taken from http://aleph.web.lal.in2p3.fr/tau/specfun.html

Source code:ALEPH_2014_I1267648.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief Add a short analysis description here class ALEPH_2014_I1267648 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(ALEPH_2014_I1267648);


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

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

  // Initialise and register projections
  declare(UnstableParticles(), "UFS");

  // Book histograms
  for (unsigned int ix = 0; ix < 5; ++ix)
    book(_h[ix], "TMP/h_" + toString(ix + 1), refData(1 + ix, 1, 1));
  book(_c, "TMP/ntau");
}


void findDecayProducts(const Particle& mother,
                       const int isign,
                       unsigned int& nstable,
                       unsigned int& npip,
                       unsigned int& npim,
                       unsigned int& npi0,
                       FourMomentum& ptot) {
  for (const Particle& p : mother.children()) {
    int id = p.pid();
    if (id == PID::KPLUS || id == PID::KMINUS) {
      ++nstable;
      ptot += p.momentum();
    }
    else if (id * isign == PID::PIPLUS) {
      ++npip;
      ++nstable;
      ptot += p.momentum();
    }
    else if (id * isign == PID::PIMINUS) {
      ++npim;
      ++nstable;
      ptot += p.momentum();
    }
    else if (id == PID::PI0) {
      ++nstable;
      ++npi0;
      ptot += p.momentum();
    }
    else if (id == PID::PHOTON)
      continue;
    else if (!p.children().empty())
      findDecayProducts(p, isign, nstable, npip, npim, npi0, ptot);
    else
      ++nstable;
  }
}


/// Perform the per-event analysis
void analyze(const Event& event) {

  // Loop over taus
  for (const Particle& tau : apply<UnstableParticles>(event, "UFS").particles(Cuts::abspid == PID::TAU)) {
    _c->fill();
    FourMomentum ptot;
    unsigned int nstable(0), npip(0), npim(0), npi0(0);
    findDecayProducts(tau, tau.pid() / tau.abspid(), nstable, npip, npim, npi0, ptot);
    // tau -> pi pi0 nu_tau (both charges)
    if (npim == 1 && npi0 == 1 && nstable == 3) _h[0]->fill(ptot.mass2());
    // tau -> pi pi0 pi0 nu_tau (both charges)
    else if (npim == 1 && npi0 == 2 && nstable == 4)
      _h[1]->fill(ptot.mass2());
    //    tau -> pi pi0 pi0 pi0         (3,1,1)
    else if (npim == 1 && npi0 == 3 && nstable == 5)
      _h[2]->fill(ptot.mass2());
    //    tau -> 3 charged pions        (4,1,1)
    else if (npim == 2 && npip == 1 && nstable == 4)
      _h[3]->fill(ptot.mass2());
    //    tau -> 3 charged pions + pi0  (5,1,1)
    else if (npim == 2 && npip == 1 && npi0 == 1 && nstable == 5)
      _h[4]->fill(ptot.mass2());
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  for (unsigned int ix = 0; ix < 5; ++ix) {
    scale(_h[ix], 100. / *_c);
    Estimate1DPtr tmp;
    book(tmp, 1 + ix, 1, 1);
    barchart(_h[ix], tmp);
  }
}

/// @}

private:

/// @name Histograms
/// @{
Histo1DPtr _h[5];
CounterPtr _c;
/// @}

};

RIVET_DECLARE_PLUGIN(ALEPH_2014_I1267648);

} ```