smash::TwoBodyDecaySemistable Class Reference

#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 173 of file decaytype.h.

Inheritance diagram for smash::TwoBodyDecaySemistable:

Collaboration diagram for smash::TwoBodyDecaySemistable:

Public Member Functions
	TwoBodyDecaySemistable (ParticleTypePtrList part_types, int l)
	Construct a TwoBodyDecaySemistable. More...
double	width (double m0, double G0, double m) const override
	Get the mass-dependent width of a two-body decay into one stable and one unstable particle according to Manley:1992yb [33]. More...
double	in_width (double m0, double G0, double m, double m1, double m2) const override
	Get the mass-dependent in-width for a resonance formation process from one stable and one unstable particle according to Manley:1992yb [33], see also Effenberger:1999wlg [18], eq. More...
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

TwoBodyDecaySemistable()

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 124 of file decaytype.cc.

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

Member Function Documentation

width()

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

overridevirtual

Get the mass-dependent width of a two-body decay into one stable and one unstable particle according to Manley:1992yb [33].

Parameters

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

Implements smash::DecayType.

Definition at line 166 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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in_width()

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

overridevirtual

Get the mass-dependent in-width for a resonance formation process from one stable and one unstable particle according to Manley:1992yb [33], see also Effenberger:1999wlg [18], eq.

(2.77).

Parameters

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

Implements smash::DecayType.

Definition at line 171 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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rho()

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 146 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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get_Lambda()

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 [10], eq. (175). For the original values used by M. Post, see table 1 in Post:2003hu [39].

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 130 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

Lambda_

double smash::TwoBodyDecaySemistable::Lambda_

protected

Cut-off parameter Λ for semi-stable decays.

Definition at line 226 of file decaytype.h.

tabulation_

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

mutableprotected

Tabulation of the resonance integrals.

Definition at line 229 of file decaytype.h.

---

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

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