celeritas::ParticleTrackView Class Reference

Read/write view to the physical properties of a single particle track. More...

#include <ParticleTrackView.hh>

Public Types
Type aliases
using	ParamsRef = celeritas::NativeCRef< ParticleParamsData >
using	StateRef = celeritas::NativeRef< ParticleStateData >
using	Initializer_t = ParticleTrackInitializer
using	Charge = units::ElementaryCharge
using	Energy = units::MevEnergy
using	Mass = units::MevMass
using	Momentum = units::MevMomentum
using	MomentumSq = units::MevMomentumSq
using	Speed = units::LightSpeed

Public Member Functions
	ParticleTrackView (ParamsRef const &params, StateRef const &states, TrackSlotId id)
	Construct from dynamic and static particle properties.
ParticleTrackView &	operator= (Initializer_t const &other)
	Initialize the particle.
void	energy (Energy)
	Change the particle's kinetic energy.
void	subtract_energy (Energy)
	Reduce the particle's energy without undergoing a collision [MeV].
ParticleId	particle_id () const
	Unique particle type identifier.
Energy	energy () const
	Kinetic energy [MeV].
bool	is_stopped () const
	Whether the track is stopped (zero kinetic energy).
ParticleView	particle_view () const
	Get static particle properties for the current state.
Mass	mass () const
	Rest mass [MeV / c^2].
Charge	charge () const
	Elementary charge.
real_type	decay_constant () const
	Decay constant in native units.
bool	is_antiparticle () const
	Whether it is an antiparticle.
bool	is_stable () const
	Whether particle is stable.
bool	is_heavy () const
	Distinguish between light (e-/e+) and heavy (muon/hadron) particles.
Energy	total_energy () const
	Kinetic energy plus rest energy [MeV].
real_type	beta_sq () const
	Square of \( \beta \), which is the fraction of lightspeed [unitless].
Speed	speed () const
	Speed [1/c].
real_type	lorentz_factor () const
	Lorentz factor [unitless].
Momentum	momentum () const
	Relativistic momentum [MeV / c].
MomentumSq	momentum_sq () const
	Square of relativistic momentum [MeV^2 / c^2].

Detailed Description

Read/write view to the physical properties of a single particle track.

These functions should be used in each physics Process or Interactor or anything else that needs to access particle properties. Assume that all these functions are expensive: when using them as accessors, locally store the results rather than calling the function repeatedly. If any of the calculations prove to be hot spots we will experiment with caching some of the variables.

Member Function Documentation

energy()

void celeritas::ParticleTrackView::energy ( Energy  quantity )

inline

Change the particle's kinetic energy.

This should only be used when the particle is in a valid state. For HEP applications, the new energy should always be less than the starting energy.

is_heavy()

bool celeritas::ParticleTrackView::is_heavy ( ) const

inline

Distinguish between light (e-/e+) and heavy (muon/hadron) particles.

Light and heavy charged particles have different parameters and treatment in continuous energy loss and Coulomb scattering. The choice of 1 MeV to distinguish between electrons and muons is arbitrary.

lorentz_factor()

real_type celeritas::ParticleTrackView::lorentz_factor ( ) const

inline

Lorentz factor [unitless].

The Lorentz factor can be viewed as a transformation from classical quantities to relativistic quantities. It's defined as

\[ \gamma = \frac{1}{\sqrt{1 - v^2 / c^2}} \]

Its value is infinite for the massless photon, and greater than or equal to 1 otherwise.

Gamma can also be calculated from the total (rest + kinetic) energy

\[ E = \gamma mc^2 = K + mc^2 \]

which we use here since K and m are the primary stored quantities of the particles:

\[ \gamma = 1 + \frac{K}{mc^2} \]

momentum()

auto celeritas::ParticleTrackView::momentum ( ) const

inline

Relativistic momentum [MeV / c].

This is calculated by taking the root of the square of the momentum.

momentum_sq()

auto celeritas::ParticleTrackView::momentum_sq ( ) const

inline

Square of relativistic momentum [MeV^2 / c^2].

Total energy:

\[ E = K + mc^2 \]

Relation between energy and momentum:

\[ E^2 = p^2 c^2 + m^2 c^4 \]

therefore

\[ p^2 = \frac{E^2}{c^2} - m^2 c^2 \]

or

\[ p^2 = \frac{K^2}{c^2} + 2 * m * K \]

speed()

auto celeritas::ParticleTrackView::speed ( ) const

inline

Speed [1/c].

\( \beta = v/c \) is calculated using the equality

\[ pc/E = \beta ; \quad \beta^2 = \frac{p^2 c^2}{E^2} \]

. Using

\[ E^2 = p^2 c^2 + m^2 c^4 \]

and

\[ E = K + mc^2 \]

the fraction of lightspeed speed is

\[ \beta = \sqrt{1 - \left( \frac{mc^2}{K + mc^2} \right)^2} = \frac{\sqrt{K(K + 2mc^2)}}{K + mc^2} \]

.

This expression works for massless particles and is robust against round-off error at low energies.

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

• phys/ParticleTrackView.hh