smash::TwoBodyDecayUnstable Class Reference

#include <decaytype.h>

TwoBodyDecayUnstable represents a decay type with two unstable final-state particles.

Definition at line 236 of file decaytype.h.

Inheritance diagram for smash::TwoBodyDecayUnstable:

Collaboration diagram for smash::TwoBodyDecayUnstable:

Public Member Functions
	TwoBodyDecayUnstable (ParticleTypePtrList part_types, int l)
	Construct a TwoBodyDecayUnstable. 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 unstable 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

TwoBodyDecayUnstable()

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

Construct a TwoBodyDecayUnstable.

Parameters

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

Returns

The constructed object.

Definition at line 182 of file decaytype.cc.

    : TwoBodyDecay(part_types, l), Lambda_(get_Lambda()), tabulation_(nullptr) {
  if (part_types[0]->is_stable() || part_types[1]->is_stable()) {
    throw std::runtime_error(
        "Error: Stable particle in TwoBodyDecayUnstable constructor: " +
        part_types[0]->pdgcode().string() + " " +
        part_types[1]->pdgcode().string());
  }
}

Member Function Documentation

width()

double smash::TwoBodyDecayUnstable::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 228 of file decaytype.cc.

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

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in_width()

double smash::TwoBodyDecayUnstable::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 232 of file decaytype.cc.

                                                       {
  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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rho()

double smash::TwoBodyDecayUnstable::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 200 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 r1 = particle_types_[0];
    const ParticleTypePtr r2 = particle_types_[1];
    const double m1_min = r1->min_mass_kinematic();
    const double m2_min = r2->min_mass_kinematic();
    const double sum_gamma = r1->width_at_pole() + r2->width_at_pole();
    const double tab_interval = std::max(2., 10. * sum_gamma);
 
    tabulation_ = make_unique<Tabulation>(
        m1_min + m2_min, tab_interval, num_tab_pts, [&](double sqrts) {
          const double m1_max = sqrts - m2_min;
          const double m2_max = sqrts - m1_min;
 
          const double result = integrate2d(m1_min, m1_max, m2_min, m2_max,
                                            [&](double m1, double m2) {
                                              return integrand_rho_Manley_2res(
                                                  sqrts, m1, m2, r1, r2, L_);
                                            })
                                    .value();
          return result;
        });
  }
  return tabulation_->get_value_linear(mass);
}

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get_Lambda()

double smash::TwoBodyDecayUnstable::get_Lambda ( )

protected

Returns

the cut-off parameter Λ for unstable decays, given the types of the daughter particles.

Definition at line 193 of file decaytype.cc.

                                        {
  // for now: use the same value for all unstable decays (fixed on f₂ → ρ ρ)
  return 0.6;
}

Member Data Documentation

Lambda_

double smash::TwoBodyDecayUnstable::Lambda_

protected

Cut-off parameter Λ for unstable decays.

Definition at line 259 of file decaytype.h.

tabulation_

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

mutableprotected

Tabulation of the resonance integrals.

Definition at line 262 of file decaytype.h.

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

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