# pylint: disable=import-outside-toplevel, too-many-arguments, too-many-lines
"""Generate an amplitude model with the helicity formalism.
.. autolink-preface::
import sympy as sp
"""
import collections
import logging
import operator
import re
import sys
from collections import OrderedDict, abc
from difflib import get_close_matches
from functools import reduce
from typing import (
TYPE_CHECKING,
Any,
DefaultDict,
Dict,
ItemsView,
Iterable,
Iterator,
KeysView,
List,
Mapping,
Optional,
Set,
Tuple,
Union,
ValuesView,
)
import attrs
import sympy as sp
from attrs import define, field, frozen
from attrs.validators import instance_of
from qrules.combinatorics import (
perform_external_edge_identical_particle_combinatorics,
)
from qrules.particle import Particle
from qrules.transition import ReactionInfo, StateTransition
from ampform.dynamics.builder import (
ResonanceDynamicsBuilder,
TwoBodyKinematicVariableSet,
create_non_dynamic,
)
from ampform.kinematics import (
HelicityAdapter,
get_helicity_angle_label,
get_invariant_mass_label,
)
from .decay import TwoBodyDecay
from .naming import (
CanonicalAmplitudeNameGenerator,
HelicityAmplitudeNameGenerator,
generate_transition_label,
)
if sys.version_info >= (3, 8):
from functools import singledispatchmethod
else:
from singledispatchmethod import singledispatchmethod
if TYPE_CHECKING:
from IPython.lib.pretty import PrettyPrinter
ParameterValue = Union[float, complex, int]
"""Allowed value types for parameters."""
[docs]class ParameterValues(abc.Mapping):
"""Ordered mapping to `ParameterValue` with convenient getter and setter.
>>> a, b, c = sp.symbols("a b c")
>>> parameters = ParameterValues({a: 0.0, b: 1+1j, c: -2})
>>> parameters[a]
0.0
>>> parameters["b"]
(1+1j)
>>> parameters["b"] = 3
>>> parameters[1]
3
>>> parameters[2]
-2
>>> parameters[2] = 3.14
>>> parameters[c]
3.14
.. automethod:: __getitem__
.. automethod:: __setitem__
"""
def __init__(self, parameters: Mapping[sp.Symbol, ParameterValue]) -> None:
self.__parameters = dict(parameters)
def __repr__(self) -> str:
return f"{type(self).__name__}({self.__parameters})"
def _repr_pretty_(self, p: "PrettyPrinter", cycle: bool) -> None:
class_name = type(self).__name__
if cycle:
p.text(f"{class_name}(...)")
else:
with p.group(indent=2, open=f"{class_name}({{"):
p.breakable()
for par, value in self.items():
p.pretty(par)
p.text(": ")
p.pretty(value)
p.text(",")
p.breakable()
p.text("})")
[docs] def __getitem__(self, key: Union[sp.Symbol, int, str]) -> "ParameterValue":
par = self._get_parameter(key)
return self.__parameters[par]
[docs] def __setitem__(
self, key: Union[sp.Symbol, int, str], value: "ParameterValue"
) -> None:
par = self._get_parameter(key)
self.__parameters[par] = value
@singledispatchmethod
def _get_parameter(self, key: Union[sp.Symbol, int, str]) -> sp.Symbol:
# pylint: disable=no-self-use
raise KeyError( # no TypeError because of sympy.core.expr.Expr.xreplace
f"Cannot find parameter for key type {type(key).__name__}"
)
@_get_parameter.register(sp.Symbol)
def _(self, par: sp.Symbol) -> sp.Symbol:
if par not in self.__parameters:
raise KeyError(f"{type(self).__name__} has no parameter {par}")
return par
@_get_parameter.register(str)
def _(self, name: str) -> sp.Symbol:
for parameter in self.__parameters:
if parameter.name == name:
return parameter
raise KeyError(f"No parameter available with name {name}")
@_get_parameter.register(int)
def _(self, key: int) -> sp.Symbol:
for i, parameter in enumerate(self.__parameters):
if i == key:
return parameter
raise KeyError(
f"Parameter mapping has {len(self)} parameters, but trying to get"
f" parameter number {key}"
)
def __len__(self) -> int:
return len(self.__parameters)
def __iter__(self) -> Iterator[sp.Symbol]:
return iter(self.__parameters)
def items(self) -> ItemsView[sp.Symbol, ParameterValue]:
return self.__parameters.items()
def keys(self) -> KeysView[sp.Symbol]:
return self.__parameters.keys()
def values(self) -> ValuesView[ParameterValue]:
return self.__parameters.values()
def _order_component_mapping(
mapping: Mapping[str, sp.Expr]
) -> "OrderedDict[str, sp.Expr]":
return collections.OrderedDict(
[(key, mapping[key]) for key in sorted(mapping, key=_natural_sorting)]
)
def _order_symbol_mapping(
mapping: Mapping[sp.Symbol, sp.Expr]
) -> "OrderedDict[sp.Symbol, sp.Expr]":
return collections.OrderedDict(
[
(symbol, mapping[symbol])
for symbol in sorted(
mapping, key=lambda s: _natural_sorting(s.name)
)
]
)
def _order_amplitudes(
mapping: Mapping[sp.Indexed, sp.Expr]
) -> "OrderedDict[str, sp.Expr]":
return collections.OrderedDict(
[
(key, mapping[key])
for key in sorted(mapping, key=lambda a: _natural_sorting(str(a)))
]
)
def _natural_sorting(text: str) -> List[Union[float, str]]:
# https://stackoverflow.com/a/5967539/13219025
return [
__attempt_number_cast(c)
for c in re.split(r"[+-]?([0-9]+(?:[.][0-9]*)?|[.][0-9]+)", text)
]
def __attempt_number_cast(text: str) -> Union[float, str]:
try:
return float(text)
except ValueError:
return text
[docs]@frozen
class HelicityModel: # noqa: R701
intensity: sp.Expr = field(validator=instance_of(sp.Expr))
"""Main expression describing the intensity over `kinematic_variables`."""
amplitudes: "OrderedDict[sp.Indexed, sp.Expr]" = field(
converter=_order_amplitudes
)
"""Definitions for the amplitudes that appear in `intensity`.
The main `intensity` is a sum over amplitudes for each initial and final
state helicity combination. These amplitudes are indicated with as
`sp.Indexed <sympy.tensor.indexed.Indexed>` instances and this attribute
provides the definitions for each of these. See also :ref:`TR-014
<compwa-org:tr-014-solution-2>`.
"""
parameter_defaults: ParameterValues = field(converter=ParameterValues)
"""A mapping of suggested parameter values.
Keys are `~sympy.core.symbol.Symbol` instances from the main
:attr:`expression` that should be interpreted as parameters (as opposed to
`kinematic_variables`). The symbols are ordered alphabetically by name with
natural sort order. Values have been extracted from the input
`~qrules.transition.ReactionInfo`.
"""
kinematic_variables: "OrderedDict[sp.Symbol, sp.Expr]" = field(
converter=_order_symbol_mapping
)
"""Expressions for converting four-momenta to kinematic variables."""
components: "OrderedDict[str, sp.Expr]" = field(
converter=_order_component_mapping
)
"""A mapping for identifying main components in the :attr:`expression`.
Keys are the component names (`str`), formatted as LaTeX, and values are
sub-expressions in the main :attr:`expression`. The mapping is an
`~collections.OrderedDict` that orders the component names alphabetically
with natural sort order.
"""
reaction_info: ReactionInfo = field(validator=instance_of(ReactionInfo))
@property
def expression(self) -> sp.Expr:
"""Expression for the `intensity` with all amplitudes fully expressed.
Constructed from `intensity` by substituting its amplitude symbols with
the definitions with `amplitudes`.
"""
return self.intensity.xreplace(self.amplitudes)
[docs] def rename_symbols( # noqa: R701
self, renames: Union[Iterable[Tuple[str, str]], Mapping[str, str]]
) -> "HelicityModel":
"""Rename certain symbols in the model.
Renames all `~sympy.core.symbol.Symbol` instance that appear in
`expression`, `parameter_defaults`, `components`, and
`kinematic_variables`. This method can be used to :ref:`couple
parameters <usage/modify:Couple parameters>`.
Args:
renames: A mapping from old to new names.
Returns:
A **new** instance of a `HelicityModel` with symbols in all
attributes renamed accordingly.
"""
renames = dict(renames)
symbols = self.__collect_symbols()
symbol_names = {s.name for s in symbols}
for name in renames:
if name not in symbol_names:
logging.warning(f"There is no symbol with name {name}")
symbol_mapping = {
s: sp.Symbol(renames[s.name], **s.assumptions0)
if s.name in renames
else s
for s in symbols
}
return attrs.evolve(
self,
intensity=self.intensity.xreplace(symbol_mapping),
amplitudes={
amp: expr.xreplace(symbol_mapping)
for amp, expr in self.amplitudes.items()
},
parameter_defaults={
symbol_mapping[par]: value
for par, value in self.parameter_defaults.items()
},
components={
name: expr.xreplace(symbol_mapping)
for name, expr in self.components.items()
},
kinematic_variables={
symbol_mapping[var]: expr.xreplace(symbol_mapping)
for var, expr in self.kinematic_variables.items()
},
)
def __collect_symbols(self) -> Set[sp.Symbol]:
symbols: Set[sp.Symbol] = self.expression.free_symbols
symbols |= set(self.kinematic_variables)
for expr in self.kinematic_variables.values():
symbols |= expr.free_symbols
return symbols
[docs] def sum_components( # noqa: R701
self, components: Iterable[str]
) -> sp.Expr:
"""Coherently or incoherently add components of a helicity model."""
components = list(components) # copy
for component in components:
if component not in self.components:
first_letter = component[0]
# pylint: disable=cell-var-from-loop
candidates = get_close_matches(
component,
filter(
lambda c: c.startswith(first_letter), self.components
),
)
raise KeyError(
f'Component "{component}" not in model components. '
"Did you mean any of these?",
candidates,
)
if any(map(lambda c: c.startswith("I"), components)) and any(
map(lambda c: c.startswith("A"), components)
):
intensity_sum = self.sum_components(
components=filter(lambda c: c.startswith("I"), components),
)
amplitude_sum = self.sum_components(
components=filter(lambda c: c.startswith("A"), components),
)
return intensity_sum + amplitude_sum
if all(map(lambda c: c.startswith("I"), components)):
return sum(self.components[c] for c in components)
if all(map(lambda c: c.startswith("A"), components)):
return abs(sum(self.components[c] for c in components)) ** 2
raise ValueError(
'Not all component names started with either "A" or "I"'
)
@define
class _HelicityModelIngredients:
parameter_defaults: Dict[sp.Symbol, ParameterValue] = field(factory=dict)
amplitudes: Dict[sp.Indexed, sp.Expr] = field(factory=dict)
components: Dict[str, sp.Expr] = field(factory=dict)
kinematic_variables: Dict[sp.Symbol, sp.Expr] = field(factory=dict)
amplitude_base: sp.IndexedBase = field(
init=False, on_setattr=attrs.setters.frozen, repr=False
)
def __attrs_post_init__(self) -> None:
# https://www.attrs.org/en/stable/init.html#post-init
base = sp.IndexedBase("A", complex=True)
object.__setattr__(self, "amplitude_base", base)
def reset(self) -> None:
self.parameter_defaults = {}
self.amplitudes = {}
self.components = {}
self.kinematic_variables = {}
[docs]class DynamicsSelector(abc.Mapping):
"""Configure which `.ResonanceDynamicsBuilder` to use for each node."""
def __init__(
self, transitions: Union[ReactionInfo, Iterable[StateTransition]]
) -> None:
if isinstance(transitions, ReactionInfo):
transitions = transitions.transitions
self.__choices: Dict[TwoBodyDecay, ResonanceDynamicsBuilder] = {}
for transition in transitions:
for node_id in transition.topology.nodes:
decay = TwoBodyDecay.from_transition(transition, node_id)
self.__choices[decay] = create_non_dynamic
[docs] @singledispatchmethod
def assign(
self, selection: Any, builder: ResonanceDynamicsBuilder
) -> None:
"""Assign a `.ResonanceDynamicsBuilder` to a selection of nodes.
Currently, the following types of selections are implements:
- `str`: Select transition nodes by the name of the
`~.TwoBodyDecay.parent` `~qrules.particle.Particle`.
- `.TwoBodyDecay` or `tuple` of a `~qrules.transition.StateTransition`
with a node ID: set dynamics for one specific transition node.
"""
raise NotImplementedError(
"Cannot set dynamics builder for selection type"
f" {type(selection).__name__}"
)
@assign.register(TwoBodyDecay)
def _(
self, decay: TwoBodyDecay, builder: ResonanceDynamicsBuilder
) -> None:
self.__choices[decay] = builder
@assign.register(tuple)
def _(
self,
transition_node: Tuple[StateTransition, int],
builder: ResonanceDynamicsBuilder,
) -> None:
decay = TwoBodyDecay.create(transition_node)
return self.assign(decay, builder)
@assign.register(str)
def _(self, particle_name: str, builder: ResonanceDynamicsBuilder) -> None:
found_particle = False
for decay in self.__choices:
decaying_particle = decay.parent.particle
if decaying_particle.name == particle_name:
self.__choices[decay] = builder
found_particle = True
if not found_particle:
logging.warning(
f'Model contains no resonance with name "{particle_name}"'
)
@assign.register(Particle)
def _(self, particle: Particle, builder: ResonanceDynamicsBuilder) -> None:
return self.assign(particle.name, builder)
def __getitem__(
self, __k: Union[TwoBodyDecay, Tuple[StateTransition, int]]
) -> ResonanceDynamicsBuilder:
__k = TwoBodyDecay.create(__k)
return self.__choices[__k]
def __len__(self) -> int:
return len(self.__choices)
def __iter__(self) -> Iterator[TwoBodyDecay]:
return iter(self.__choices)
def items(self) -> ItemsView[TwoBodyDecay, ResonanceDynamicsBuilder]:
return self.__choices.items()
def keys(self) -> KeysView[TwoBodyDecay]:
return self.__choices.keys()
def values(self) -> ValuesView[ResonanceDynamicsBuilder]:
return self.__choices.values()
[docs]class HelicityAmplitudeBuilder: # pylint: disable=too-many-instance-attributes
r"""Amplitude model generator for the helicity formalism.
Args:
reaction: The `~qrules.transition.ReactionInfo` from which to
:meth:`formulate` an amplitude model.
stable_final_state_ids: Put final state 'invariant' masses
(:math:`m_0, m_1, \dots`) under `.HelicityModel.parameter_defaults`
(with a *scalar* suggested value) instead of
`~.HelicityModel.kinematic_variables` (which are expressions to
compute an event-wise array of invariant masses). This is useful
if final state particles are stable.
stable_final_state_ids: Put the invariant of the initial state
(:math:`m_{012\dots}`) under `.HelicityModel.parameter_defaults`
(with a *scalar* suggested value) instead of
`~.HelicityModel.kinematic_variables`. This is useful if
four-momenta were generated with or kinematically fit to a specific
initial state energy.
.. seealso:: :ref:`usage/amplitude:Scalar masses`
"""
def __init__(
self,
reaction: ReactionInfo,
stable_final_state_ids: Optional[Iterable[int]] = None,
scalar_initial_state_mass: bool = False,
) -> None:
if len(reaction.transitions) < 1:
raise ValueError(
f"At least one {StateTransition.__name__} required to"
" genenerate an amplitude model!"
)
self._name_generator = HelicityAmplitudeNameGenerator()
self.__reaction = reaction
self.__ingredients = _HelicityModelIngredients()
self.__dynamics_choices = DynamicsSelector(reaction)
self.__adapter = HelicityAdapter(reaction)
self.stable_final_state_ids = stable_final_state_ids # type: ignore[assignment]
self.scalar_initial_state_mass = scalar_initial_state_mass # type: ignore[assignment]
@property
def adapter(self) -> HelicityAdapter:
"""Converter for computing kinematic variables from four-momenta."""
return self.__adapter
@property
def dynamics_choices(self) -> DynamicsSelector:
return self.__dynamics_choices
@property
def stable_final_state_ids(self) -> Optional[Set[int]]:
# noqa: D403
"""IDs of the final states that should be considered stable.
The 'invariant' mass symbols for these final states will be inserted as
**scalar** values into the `.parameter_defaults`.
"""
return self.__stable_final_state_ids
@stable_final_state_ids.setter
def stable_final_state_ids(self, value: Optional[Iterable[int]]) -> None:
self.__stable_final_state_ids = None
if value is not None:
self.__stable_final_state_ids = set(value)
if not self.__stable_final_state_ids <= set(
self.__reaction.final_state
):
raise ValueError(
"Final state IDs are"
f" {sorted(self.__reaction.final_state)}, but trying to"
" set stable final state IDs"
f" {self.__stable_final_state_ids}"
)
@property
def scalar_initial_state_mass(self) -> bool:
"""Add initial state mass as scalar value to `.parameter_defaults`.
.. seealso:: :ref:`usage/amplitude:Scalar masses`
"""
return self.__scalar_initial_state_mass
@scalar_initial_state_mass.setter
def scalar_initial_state_mass(self, value: bool) -> None:
if not isinstance(value, bool):
raise TypeError
self.__scalar_initial_state_mass = value
[docs] def set_dynamics(
self, particle_name: str, dynamics_builder: ResonanceDynamicsBuilder
) -> None:
self.__dynamics_choices.assign(particle_name, dynamics_builder)
def __formulate_top_expression(self) -> sp.Expr:
transition_groups = group_transitions(self.__reaction.transitions)
self.__register_parameter_couplings(transition_groups)
coherent_intensities = [
self.__formulate_coherent_intensity(group)
for group in transition_groups
]
return sum(coherent_intensities)
def __register_parameter_couplings(
self, transition_groups: List[List[StateTransition]]
) -> None:
for graph_group in transition_groups:
for transition in graph_group:
self._name_generator.register_amplitude_coefficient_name(
transition
)
def __formulate_coherent_intensity(
self, transition_group: List[StateTransition]
) -> sp.Expr:
transition = transition_group[0]
graph_group_label = generate_transition_label(transition)
sequential_expressions: List[sp.Expr] = []
for group in transition_group:
sequential_graphs = (
perform_external_edge_identical_particle_combinatorics(
group.to_graph()
)
)
for graph in sequential_graphs:
transition = StateTransition.from_graph(graph)
expression = self.__formulate_sequential_decay(transition)
sequential_expressions.append(expression)
outer_state_ids = list(transition.initial_states)
outer_state_ids += sorted(transition.final_states)
helicities = tuple(
sp.Rational(transition.states[i].spin_projection)
for i in outer_state_ids
)
amplitude_symbol = self.__ingredients.amplitude_base[helicities]
amplitude_sum = sum(sequential_expressions)
self.__ingredients.amplitudes[amplitude_symbol] = amplitude_sum
component_name = f"I_{{{graph_group_label}}}"
self.__ingredients.components[component_name] = abs(amplitude_sum) ** 2
return abs(amplitude_symbol) ** 2
def __formulate_sequential_decay(
self, transition: StateTransition
) -> sp.Expr:
partial_decays: List[sp.Expr] = [
self._formulate_partial_decay(transition, node_id)
for node_id in transition.topology.nodes
]
sequential_amplitudes = reduce(operator.mul, partial_decays)
coefficient = self.__generate_amplitude_coefficient(transition)
prefactor = self.__generate_amplitude_prefactor(transition)
expression = coefficient * sequential_amplitudes
if prefactor is not None:
expression = prefactor * expression
subscript = self._name_generator.generate_amplitude_name(transition)
self.__ingredients.components[f"A_{{{subscript}}}"] = expression
return expression
def _formulate_partial_decay(
self, transition: StateTransition, node_id: int
) -> sp.Expr:
wigner_d = formulate_wigner_d(transition, node_id)
dynamics = self.__formulate_dynamics(transition, node_id)
return wigner_d * dynamics
def __formulate_dynamics(
self, transition: StateTransition, node_id: int
) -> sp.Expr:
decay = TwoBodyDecay.from_transition(transition, node_id)
if decay not in self.__dynamics_choices:
return 1
builder = self.__dynamics_choices[decay]
variable_set = _generate_kinematic_variable_set(transition, node_id)
expression, parameters = builder(decay.parent.particle, variable_set)
for par, value in parameters.items():
if par in self.__ingredients.parameter_defaults:
previous_value = self.__ingredients.parameter_defaults[par]
if value != previous_value:
logging.warning(
f'New default value {value} for parameter "{par.name}"'
" is inconsistent with existing value"
f" {previous_value}"
)
self.__ingredients.parameter_defaults[par] = value
return expression
def __generate_amplitude_coefficient(
self, transition: StateTransition
) -> sp.Symbol:
"""Generate coefficient parameter for a sequential amplitude.
Generally, each partial amplitude of a sequential amplitude transition
should check itself if it or a parity partner is already defined. If so
a coupled coefficient is introduced.
"""
suffix = self._name_generator.generate_sequential_amplitude_suffix(
transition
)
symbol = sp.Symbol(f"C_{{{suffix}}}")
value = complex(1, 0)
self.__ingredients.parameter_defaults[symbol] = value
return symbol
def __generate_amplitude_prefactor(
self, transition: StateTransition
) -> Optional[float]:
prefactor = get_prefactor(transition)
if prefactor != 1.0:
for node_id in transition.topology.nodes:
raw_suffix = self._name_generator.generate_coefficient_name(
transition, node_id
)
if (
raw_suffix
in self._name_generator.parity_partner_coefficient_mapping
):
coefficient_suffix = self._name_generator.parity_partner_coefficient_mapping[
raw_suffix
]
if coefficient_suffix != raw_suffix:
return prefactor
return None
[docs]class CanonicalAmplitudeBuilder(HelicityAmplitudeBuilder):
r"""Amplitude model generator for the canonical helicity formalism.
This class defines a full amplitude in the canonical formalism, using the
helicity formalism as a foundation. The key here is that we take the full
helicity intensity as a template, and just exchange the helicity amplitudes
:math:`F` as a sum of canonical amplitudes :math:`A`:
.. math::
F^J_{\lambda_1,\lambda_2} = \sum_{LS} \mathrm{norm}(A^J_{LS})C^2.
Here, :math:`C` stands for `Clebsch-Gordan factor
<https://en.wikipedia.org/wiki/Clebsch%E2%80%93Gordan_coefficients>`_.
.. seealso:: `HelicityAmplitudeBuilder` and :doc:`/usage/formalism`.
"""
def __init__(self, reaction_result: ReactionInfo) -> None:
super().__init__(reaction_result)
self._name_generator = CanonicalAmplitudeNameGenerator()
def _formulate_partial_decay(
self, transition: StateTransition, node_id: int
) -> sp.Expr:
amplitude = super()._formulate_partial_decay(transition, node_id)
cg_coefficients = formulate_clebsch_gordan_coefficients(
transition, node_id
)
return cg_coefficients * amplitude
[docs]def get_prefactor(transition: StateTransition) -> float:
"""Calculate the product of all prefactors defined in this transition.
.. seealso:: `qrules.quantum_numbers.InteractionProperties.parity_prefactor`
"""
prefactor = 1.0
for node_id in transition.topology.nodes:
interaction = transition.interactions[node_id]
if interaction and interaction.parity_prefactor is not None:
prefactor *= interaction.parity_prefactor
return prefactor
[docs]def group_transitions(
transitions: Iterable[StateTransition],
) -> List[List[StateTransition]]:
"""Match final and initial states in groups.
Each `~qrules.transition.StateTransition` corresponds to a specific state
transition amplitude. This function groups together transitions, which have
the same initial and final state (including spin). This is needed to
determine the coherency of the individual amplitude parts.
"""
transition_groups: DefaultDict[
Tuple[
Tuple[Tuple[str, float], ...],
Tuple[Tuple[str, float], ...],
],
List[StateTransition],
] = collections.defaultdict(list)
for transition in transitions:
initial_state = sorted(
(
transition.states[i].particle.name,
transition.states[i].spin_projection,
)
for i in transition.topology.incoming_edge_ids
)
final_state = sorted(
(
transition.states[i].particle.name,
transition.states[i].spin_projection,
)
for i in transition.topology.outgoing_edge_ids
)
group_key = (tuple(initial_state), tuple(final_state))
transition_groups[group_key].append(transition)
return list(transition_groups.values())
def _generate_kinematic_variable_set(
transition: StateTransition, node_id: int
) -> TwoBodyKinematicVariableSet:
decay = TwoBodyDecay.from_transition(transition, node_id)
inv_mass, phi, theta = _generate_kinematic_variables(transition, node_id)
child1_mass = sp.Symbol(
get_invariant_mass_label(transition.topology, decay.children[0].id),
real=True,
)
child2_mass = sp.Symbol(
get_invariant_mass_label(transition.topology, decay.children[1].id),
real=True,
)
angular_momentum: Optional[int] = decay.interaction.l_magnitude
if angular_momentum is None:
if decay.parent.particle.spin.is_integer():
angular_momentum = int(decay.parent.particle.spin)
return TwoBodyKinematicVariableSet(
incoming_state_mass=inv_mass,
outgoing_state_mass1=child1_mass,
outgoing_state_mass2=child2_mass,
helicity_theta=theta,
helicity_phi=phi,
angular_momentum=angular_momentum,
)
def _generate_kinematic_variables(
transition: StateTransition, node_id: int
) -> Tuple[sp.Symbol, sp.Symbol, sp.Symbol]:
"""Generate symbol for invariant mass, phi angle, and theta angle."""
decay = TwoBodyDecay.from_transition(transition, node_id)
phi_label, theta_label = get_helicity_angle_label(
transition.topology, decay.children[0].id
)
inv_mass_label = get_invariant_mass_label(
transition.topology, decay.parent.id
)
return (
sp.Symbol(inv_mass_label, real=True),
sp.Symbol(phi_label, real=True),
sp.Symbol(theta_label, real=True),
)
