#include <decaytype.h>

TwoBodyDecaySemistable represents a decay type with two final-state particles, one of which is stable and the other is unstable.

Definition at line 154 of file decaytype.h.

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Public Member Functions
	TwoBodyDecaySemistable (ParticleTypePtrList part_types, int l)
	Construct a TwoBodyDecaySemistable. More...

double	width (double m0, double G0, double m) const override

double	in_width (double m0, double G0, double m, double m1, double m2) const override

Public Member Functions inherited from smash::TwoBodyDecay
	TwoBodyDecay (ParticleTypePtrList part_types, int l)
	Construct a TwoBodyDecay. More...

unsigned int	particle_number () const override

bool	has_particles (ParticleTypePtrList list) const override

double	threshold () const

Public Member Functions inherited from smash::DecayType
	DecayType (ParticleTypePtrList part_types, int l)
	Construct a DecayType. More...

virtual	~DecayType ()=default
	Virtual Destructor. More...

virtual bool	has_mother (ParticleTypePtr mother) const

const ParticleTypePtrList &	particle_types () const

int	angular_momentum () const

Protected Member Functions
double	rho (double m) const override
	This is a virtual helper method which is used to write the width as Gamma(m) = Gamma_0 * rho(m) / rho(m_0). More...

double	get_Lambda ()

Protected Attributes
double	Lambda_
	Cut-off parameter Λ for semi-stable decays. More...

std::unique_ptr< Tabulation >	tabulation_
	Tabulation of the resonance integrals. More...

Protected Attributes inherited from smash::DecayType
ParticleTypePtrList	particle_types_
	final-state particles of the decay More...

int	L_
	angular momentum of the decay More...

Constructor & Destructor Documentation

smash::TwoBodyDecaySemistable::TwoBodyDecaySemistable	(	ParticleTypePtrList	part_types,
		int	l
	)

Construct a TwoBodyDecaySemistable.

Parameters

[in]	part_types	Final-state particles of the decay.
[in]	l	Angular momentum of the decay.

Returns: The constructed object.

Definition at line 127 of file decaytype.cc.

     : TwoBodyDecay(arrange_particles(part_types), l),
       Lambda_(get_Lambda()),
       tabulation_(nullptr) {}

Member Function Documentation

double smash::TwoBodyDecaySemistable::width	(	double	m0,
		double	G0,
		double	m
	)		const

overridevirtual

Returns: the mass-dependent width of the decay.

Parameters

[in]	m0	Pole mass of the decaying particle [GeV].
[in]	G0	Partial width at the pole mass [GeV].
[in]	m	Actual mass of the decaying particle [GeV].

Implements smash::DecayType.

Definition at line 169 of file decaytype.cc.

                                                                          {
   assert(rho(m0) != 0);
   return G0 * rho(m) / rho(m0) * post_ff_sqr(m, m0, threshold(), Lambda_);
 }

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double smash::TwoBodyDecaySemistable::in_width	(	double	m0,
		double	G0,
		double	m,
		double	m1,
		double	m2
	)		const

overridevirtual

Returns: The mass-dependent in-width for a resonance formation process.

Parameters

[in]	m0	Pole mass of the produced resonance [GeV].
[in]	G0	Partial width at the pole mass [GeV].
[in]	m	Actual mass of the produced resonance [GeV].
[in]	m1	Actual mass of the first incoming particle [GeV].
[in]	m2	Actual mass of the second incoming particle [GeV].

Implements smash::DecayType.

Definition at line 174 of file decaytype.cc.

                                                                     {
   assert(rho(m0) != 0);
   const double p_f = pCM(m, m1, m2);
 
   return G0 * p_f * blatt_weisskopf_sqr(p_f, L_) *
          post_ff_sqr(m, m0, threshold(), Lambda_) / (m * rho(m0));
 }

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double smash::TwoBodyDecaySemistable::rho ( double mass ) const

overrideprotectedvirtual

This is a virtual helper method which is used to write the width as Gamma(m) = Gamma_0 * rho(m) / rho(m_0).

This ensures that the width is properly normalized at the pole mass to Gamma(m_0) = Gamma_0. By default rho simply equals one, which corresponds to a constant width.

Parameters

[in] mass Resonance mass of the decay.

Returns: Width of the decay at the given mass.

Reimplemented from smash::TwoBodyDecay.

Definition at line 149 of file decaytype.cc.

                                                     {
   if (tabulation_ == nullptr) {
     /* TODO(weil): Move this lazy init to a global initialization function,
      * in order to avoid race conditions in multi-threading. */
     const ParticleTypePtr res = particle_types_[1];
     const double tabulation_interval = std::max(2., 10. * res->width_at_pole());
     const double m_stable = particle_types_[0]->mass();
     const double mres_min = res->min_mass_kinematic();
 
     tabulation_ = make_unique<Tabulation>(
         threshold(), tabulation_interval, num_tab_pts, [&](double sqrts) {
           const double mres_max = sqrts - m_stable;
           return integrate(mres_min, mres_max, [&](double m) {
             return integrand_rho_Manley_1res(sqrts, m, m_stable, res, L_);
           });
         });
   }
   return tabulation_->get_value_linear(mass);
 }

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double smash::TwoBodyDecaySemistable::get_Lambda ( )

protected

Returns: the cutoff parameter Λ for semi-stable decays, given the types of the daughter particles.

For the values used in GiBUU, see Buss:2011mx, eq. (175). For the original values used by M. Post, see table 1 in Post:2003hu.

We mostly stick to the GiBUU values, but use a different value for the ρπ decay, in order to avoid secondary bumps in the ω spectral function and achieve a better normalization. In contrast to smash, GiBUU does not have an ω → ρ π decay.

Definition at line 133 of file decaytype.cc.

                                           {
   // "semi-stable" decays (first daughter is stable and second one unstable)
   if (particle_types_[1]->baryon_number() != 0) {
     return 2.;  // unstable baryons
   } else if (particle_types_[1]->pdgcode().is_rho() &&
              particle_types_[0]->pdgcode().is_pion()) {
     return 0.8;  // ρ+π
   } else {
     return 1.6;  // other unstable mesons
   }
 }

Member Data Documentation

double smash::TwoBodyDecaySemistable::Lambda_

protected

Cut-off parameter Λ for semi-stable decays.

Definition at line 188 of file decaytype.h.

std::unique_ptr<Tabulation> smash::TwoBodyDecaySemistable::tabulation_

mutableprotected

Tabulation of the resonance integrals.

Definition at line 191 of file decaytype.h.

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

src/include/smash/decaytype.h
src/decaytype.cc

Public Member Functions

Protected Member Functions

Protected Attributes

Constructor & Destructor Documentation

Member Function Documentation

Member Data Documentation