#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:

Collaboration diagram for smash::DecayActionsFinder:

Public Member Functions
	DecayActionsFinder (const ExperimentParameters &par)
	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) 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_
	Multiplicative factor to be applied to resonance lifetimes. More...

const bool	ignore_minimum_width_at_end_
	Do all non-strong decays (including weak and electro-magnetic ones) More...

const bool	force_decays_at_end_
	Whether to find final decay actions. More...

const bool	decay_initial_particles_
	Whether to initial state particles can decay. More...

const SpinInteractionType	spin_interaction_type_
	Spin interaction type. More...

const CharmRescattering	charm_rescattering_method_
	Charm rescattering method. More...

Constructor & Destructor Documentation

◆ DecayActionsFinder()

smash::DecayActionsFinder::DecayActionsFinder ( const ExperimentParameters & par )

inlineexplicit

Initialize the finder.

Parameters

[in] par parameters from Experiment

Definition at line 33 of file decayactionsfinder.h.

       : res_lifetime_factor_(par.res_lifetime_factor),
         ignore_minimum_width_at_end_(par.ignore_minimum_width_at_end),
         force_decays_at_end_(par.force_decays_at_end),
         decay_initial_particles_(par.decay_initial_particles),
         spin_interaction_type_(par.spin_interaction_type),
         charm_rescattering_method_(par.charm_rescattering) {}

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;
     }
     /* Prevent decays of charmed particles if 'Charm_Rescattering_Method' is set
      * to 'none' and D* meson decays if set to 'T-matrix'. Adding it in this
      * function ensures that find_final_actions will still lead to forced decays
      * for all charmed hardons if 'Force_Decays_At_End' is set to true. */
     if ((charm_rescattering_method_ == CharmRescattering::None &&
          p.type().pdgcode().frac_charm() != 0) ||
         (charm_rescattering_method_ == CharmRescattering::T_Matrix &&
          p.type().pdgcode().is_Dstar2007())) {
       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, spin_interaction_type_);
       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 53 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 60 of file decayactionsfinder.h.

                                                     {
     return {};
   }

◆ find_final_actions()

ActionList smash::DecayActionsFinder::find_final_actions ( const Particles & search_list ) const

overridevirtual

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

Parameters

[in] search_list All particles at the end of simulation.

Returns: List with the found (Decay)Action objects.

Implements smash::ActionFinderInterface.

Definition at line 85 of file decayactionsfinder.cc.

                                         {
   ActionList actions;
   if (force_decays_at_end_) {
     for (const auto &p : search_list) {
       if (!ignore_minimum_width_at_end_ && p.type().is_stable()) {
         continue;  // particle is stable with respect to strong interaction
       }
       if (!decay_initial_particles_ &&
           p.get_history().collisions_per_particle == 0) {
         continue;
       }
       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., spin_interaction_type_);
       act->add_decays(p.type().get_partial_widths(
           p.momentum(), p.position().threevec(), WhichDecaymodes::All));
       actions.emplace_back(std::move(act));
     }
   }
   return actions;
 }