Helicity

Symbolica documentation for getting started, symbolic expressions, numerical evaluation, pattern matching, and APIs in Python and Rust.

`Helicity`

class Helicity

A spin projection along a particle’s direction of motion.

HEP represents the physical minus, longitudinal, and plus helicity states by the integers -1, 0, and 1.

Examples

from symbolica.community import hepkit as hep
incoming_fermion_helicity = hep.Helicity(-1)
incoming_fermion_helicity == hep.Helicity.MINUS
True

Parameters

value (int) Helicity value; must be -1, 0, or 1.

Attributes

Name	Description
`MINUS`	Return the negative-helicity singleton.
`PLUS`	Return the positive-helicity singleton.
`value`	Return the helicity as -1, 0, or 1.
`ZERO`	Return the zero-helicity singleton.

`MINUS`

MINUS: Helicity

Return the negative-helicity singleton.

Examples

int(Helicity.MINUS)
-1

`PLUS`

PLUS: Helicity

Return the positive-helicity singleton.

Examples

int(Helicity.PLUS)
1

`value`

Helicity.value: builtins.int

Return the helicity as -1, 0, or 1.

Examples

Using the setup in the Helicity class example:

hep.Helicity.PLUS.value
1

`ZERO`

ZERO: Helicity

Return the zero-helicity singleton.

Examples

int(Helicity.ZERO)
0

Methods

Name	Description
`__eq__`	Compare with another helicity value.
`__int__`	Convert this helicity to its integer value.
`__new__`	Construct a physical helicity from -1, 0, or 1.
`__repr__`	Return an evaluable-style representation of this helicity.
`parse`	Parse a named, signed, or integer helicity value.

`eq`

Helicity.__eq__(other: typing.Any) -> builtins.bool

Compare with another helicity value.

Examples

Using the setup in the Helicity class example:

hep.Helicity(0) == hep.Helicity.ZERO
True

Parameters

other (object) Object to compare with this helicity value.

`int`

Helicity.__int__() -> builtins.int

Convert this helicity to its integer value.

Examples

Using the setup in the Helicity class example:

int(hep.Helicity.MINUS)
-1

`new`

Helicity.__new__(value: builtins.int) -> Helicity

Construct a physical helicity from -1, 0, or 1.

Examples

Using the setup in the Helicity class example:

helicity = hep.Helicity(-1)

Parameters

value (int) Integer helicity value.

`repr`

Helicity.__repr__() -> builtins.str

Return an evaluable-style representation of this helicity.

Examples

Using the setup in the Helicity class example:

print(f"selected external helicity: {hep.Helicity.PLUS!r}")

`parse`

Helicity.parse(value: builtins.str) -> Helicity

Parse a named, signed, or integer helicity value.

Examples

Using the setup in the Helicity class example:

hep.Helicity.parse("+") == hep.Helicity.PLUS
True

Parameters

value (str) Helicity spelling such as "-", "0", or "+".