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

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 cacheing some of the variables.

Member Function Documentation

beta_sq()

CELER_FUNCTION real_type celeritas::ParticleTrackView::beta_sq ( ) const

inline

Square of \( \beta \), which is the fraction of lightspeed [unitless].

Beta 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 square of the fraction of lightspeed speed is

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

where \( \gamma \) is the Lorentz factor (see below).

By choosing not to divide out the mass, this expression will work for massless particles.

Todo:

For nonrelativistic particles (low kinetic energy) this expression may be inaccurate due to rounding error. It is however guaranteed to be in the exact range [0, 1].

energy()

CELER_FUNCTION 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.

lorentz_factor()

CELER_FUNCTION 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 ues here since K and m are the primary stored quantities of the particles:

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

momentum()

CELER_FUNCTION 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()

CELER_FUNCTION 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()

CELER_FUNCTION auto celeritas::ParticleTrackView::speed ( ) const

inline

Speed [1/c].

Speed is calculated using beta so that the expression works for massless particles.

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

• phys/ParticleTrackView.hh