smash::DecayActionsFinder Class Reference

#include <decayactionsfinder.h>

A simple decay finder: Just loops through all particles and checks if they can decay during the next timestep.

Definition at line 26 of file decayactionsfinder.h.

Inheritance diagram for smash::DecayActionsFinder:

Public Member Functions
	DecayActionsFinder (double res_lifetime_factor, bool do_weak_decays)
	Initialize the finder. More...
ActionList	find_actions_in_cell (const ParticleList &search_list, double dt, const double, const std::vector< FourVector > &) const override
	Check the whole particle list for decays. More...
ActionList	find_actions_with_neighbors (const ParticleList &, const ParticleList &, double, const std::vector< FourVector > &) const override
	Ignore the neighbor searches for decays. More...
ActionList	find_actions_with_surrounding_particles (const ParticleList &, const Particles &, double, const std::vector< FourVector > &) const override
	Ignore the surrounding searches for decays. More...
ActionList	find_final_actions (const Particles &search_list, bool only_res=false) const override
	Force all resonances to decay at the end of the simulation. More...
Public Member Functions inherited from smash::ActionFinderInterface
virtual	~ActionFinderInterface ()=default

Public Attributes
const double	res_lifetime_factor_ = 1.
	Multiplicative factor to be applied to resonance lifetimes. More...
const bool	do_final_weak_decays_
	Do weak decays at the end? Weak here means all non-strong decays, so electro-magnetic decays are done as well. More...
const bool	decay_initial_particles_
	Whether to initial state particles can decay. More...

Constructor & Destructor Documentation

DecayActionsFinder()

smash::DecayActionsFinder::DecayActionsFinder ( double  res_lifetime_factor, bool  do_weak_decays  )

inlineexplicit

Initialize the finder.

Parameters

[in]	res_lifetime_factor	The multiplicative factor to be applied to resonance lifetimes; default is 1
[in]	do_weak_decays	whether to perform weak decays at the end

Definition at line 35 of file decayactionsfinder.h.

      : res_lifetime_factor_(res_lifetime_factor),
        do_final_weak_decays_(do_weak_decays) {}

Member Function Documentation

find_actions_in_cell()

ActionList smash::DecayActionsFinder::find_actions_in_cell ( const ParticleList &  search_list, double  dt, const double  , const std::vector< FourVector > &    ) const

overridevirtual

Check the whole particle list for decays.

Parameters

[in]	search_list	All particles in grid cell.
[in]	dt	Size of timestep [fm]

Returns

List with the found (Decay)Action objects.

Implements smash::ActionFinderInterface.

Definition at line 20 of file decayactionsfinder.cc.

                                         {
  ActionList actions;
  /* for short time steps this seems reasonable to expect
   * less than 10 decays in most time steps */
  actions.reserve(10);
 
  for (const auto &p : search_list) {
    if (p.type().is_stable()) {
      continue;  // particle doesn't decay
    }
 
    if (!decay_initial_particles_ &&
        p.get_history().collisions_per_particle == 0) {
      continue;
    }
 
    DecayBranchList processes = p.type().get_partial_widths(
        p.momentum(), p.position().threevec(), WhichDecaymodes::Hadronic);
    // total decay width (mass-dependent)
    const double width = total_weight<DecayBranch>(processes);
 
    // check if there are any (hadronic) decays
    if (!(width > 0.0)) {
      continue;
    }
 
    constexpr double one_over_hbarc = 1. / hbarc;
 
    /* The decay_time is sampled from an exponential distribution.
     * Even though it may seem suspicious that it is sampled every
     * timestep, it can be proven that this still overall obeys
     * the exponential decay law.
     */
    double decay_time =
        res_lifetime_factor_ * random::exponential<double>(
                                   /* The clock goes slower in the rest
                                    * frame of the resonance */
                                   one_over_hbarc * p.inverse_gamma() * width);
    /* If the particle is not yet formed, shift the decay time by the time it
     * takes the particle to form */
    if (p.xsec_scaling_factor() < 1.0) {
      decay_time += p.formation_time() - p.position().x0();
    }
    if (decay_time < dt) {
      /* => decay_time ∈ [0, dt[
       * => the particle decays in this timestep. */
      auto act = std::make_unique<DecayAction>(p, decay_time);
      act->add_decays(std::move(processes));
      actions.emplace_back(std::move(act));
    }
  }
  return actions;
}

find_actions_with_neighbors()

ActionList smash::DecayActionsFinder::find_actions_with_neighbors ( const ParticleList &  , const ParticleList &  , double  , const std::vector< FourVector > &    ) const

inlineoverridevirtual

Ignore the neighbor searches for decays.

Implements smash::ActionFinderInterface.

Definition at line 51 of file decayactionsfinder.h.

                                                    {
    return {};
  }

find_actions_with_surrounding_particles()

ActionList smash::DecayActionsFinder::find_actions_with_surrounding_particles ( const ParticleList &  , const Particles &  , double  , const std::vector< FourVector > &    ) const

inlineoverridevirtual

Ignore the surrounding searches for decays.

Implements smash::ActionFinderInterface.

Definition at line 58 of file decayactionsfinder.h.

                                                    {
    return {};
  }

find_final_actions()

ActionList smash::DecayActionsFinder::find_final_actions ( const Particles &  search_list, bool  only_res = false  ) const

overridevirtual

Force all resonances to decay at the end of the simulation.

Parameters

[in]	search_list	All particles at the end of simulation.
[in]	only_res	optional parameter that requests that only actions regarding resonances are considered (disregarding stable particles)

Returns

List with the found (Decay)Action objects.

Implements smash::ActionFinderInterface.

Definition at line 76 of file decayactionsfinder.cc.

                                                                {
  ActionList actions;
 
  for (const auto &p : search_list) {
    if (!do_final_weak_decays_ && p.type().is_stable()) {
      continue;  // particle is stable with respect to strong interaction
    }
 
    if (p.type().decay_modes().is_empty()) {
      continue;  // particle cannot decay (not even e.m. or weakly)
    }
 
    auto act = std::make_unique<DecayAction>(p, 0.);
    act->add_decays(p.type().get_partial_widths(
        p.momentum(), p.position().threevec(), WhichDecaymodes::All));
    actions.emplace_back(std::move(act));
  }
  return actions;
}

Member Data Documentation

res_lifetime_factor_

const double smash::DecayActionsFinder::res_lifetime_factor_ = 1.

Multiplicative factor to be applied to resonance lifetimes.

Definition at line 77 of file decayactionsfinder.h.

do_final_weak_decays_

const bool smash::DecayActionsFinder::do_final_weak_decays_

Do weak decays at the end? Weak here means all non-strong decays, so electro-magnetic decays are done as well.

Definition at line 83 of file decayactionsfinder.h.

decay_initial_particles_

const bool smash::DecayActionsFinder::decay_initial_particles_

Initial value:

=
      InputKeys::collTerm_decayInitial.default_value()

Whether to initial state particles can decay.

Useful for analyzing interactions involving one or more resonances.

Definition at line 89 of file decayactionsfinder.h.

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The documentation for this class was generated from the following files:

• src/include/smash/decayactionsfinder.h
• src/decayactionsfinder.cc