#include "Generators/Trigger.h"

#include "TParticle.h"

int counterAll = 0;

int counterSel = 0;

bool has_gamma_converted(const TParticle& gamma, const std::vector<TParticle>& particles)

{

if (gamma.GetPdgCode() != 22) return false; // not a photon

if (gamma.GetNDaughters() != 2) return false; // did not produce 2 particles

auto& d1 = particles[gamma.GetFirstDaughter()];

auto& d2 = particles[gamma.GetLastDaughter()];

if (abs(d1.GetPdgCode()) != 11 || abs(d2.GetPdgCode()) != 11) return false; // not e+e- pair;

if (d1.R() > 100. || d2.R() > 100.) return false; // both at R < 100 cm

return true;

};

bool has_pi0_converted(const TParticle& pi0, const std::vector<TParticle>& particles)

{

if (pi0.GetPdgCode() != 111) return false;

if (std::fabs(pi0.Eta()) > 1.0) return false;

if (pi0.GetNDaughters() != 2) return false;

auto& d1 = particles[pi0.GetFirstDaughter()];

auto& d2 = particles[pi0.GetLastDaughter()];

return ( has_gamma_converted(d1, particles) && has_gamma_converted(d2, particles) );

};

o2::eventgen::Trigger

trigger_pi0()

{

auto trigger = [](const std::vector<TParticle>& particles) -> bool {

counterAll++;

for (const auto& particle : particles)

if (has_pi0_converted(particle, particles)) {

counterSel++;

std::cout << " --- event selected: " << counterSel << " / " << counterAll << std::endl;

return true;

}

std::cout << " --- event rejected: " << counterSel << " / " << counterAll << std::endl;

return false;

};

return trigger;

}