# cspell:ignore Asner Nakamura
# pylint: disable=invalid-name,protected-access,unused-argument
"""Lineshape functions that describe the dynamics.
.. seealso:: :doc:`/usage/dynamics/lineshapes`
"""
from abc import abstractmethod
from typing import Any, Callable, Type
import sympy as sp
from sympy.printing.latex import LatexPrinter
[docs]class UnevaluatedExpression(sp.Expr):
@abstractmethod
def evaluate(self) -> sp.Expr:
pass
@abstractmethod
def _latex(self, printer: LatexPrinter, *args: Any) -> str:
"""Provide a mathematical Latex representation for notebooks."""
args = tuple(map(printer._print, self.args))
return f"{self.__class__.__name__}{args}"
[docs]def implement_expr(
n_args: int,
) -> Callable[[Type[UnevaluatedExpression]], sp.Expr]:
"""Decorator for classes that derive from `UnevaluatedExpression`.
Implement a `~object.__new__` and `~sympy.core.basic.Basic.doit` method for
a class that derives from `~sympy.core.expr.Expr` (via
`UnevaluatedExpression`). It is important to derive from :code:`evaluate()`
method has to be implemented
"""
def decorator(decorated_class: Type[UnevaluatedExpression]) -> sp.Expr:
def new_method(
cls: Type,
*args: sp.Symbol,
**hints: Any,
) -> bool:
if len(args) != n_args:
raise ValueError(
f"{n_args} parameters expected, got {len(args)}"
)
args = sp.sympify(args)
evaluate = hints.get("evaluate", False)
if evaluate:
return sp.Expr.__new__(cls, *args).evaluate() # type: ignore # pylint: disable=no-member
return sp.Expr.__new__(cls, *args)
def doit_method(self: Any, **hints: Any) -> sp.Expr:
return type(self)(*self.args, **hints, evaluate=True)
decorated_class.__new__ = new_method # type: ignore
decorated_class.doit = doit_method
return decorated_class
return decorator
[docs]@implement_expr(n_args=3)
class BlattWeisskopf(UnevaluatedExpression):
r"""Blatt-Weisskopf function :math:`B_L`, up to :math:`L \leq 4`.
Args:
q: Break-up momentum. Can be computed with `breakup_momentum`.
d: impact parameter :math:`d`, also called meson radius. Usually of the
order 1 fm.
angular_momentum: Angular momentum :math:`L` of the decaying particle.
.. glue:math:: BlattWeisskopf
:label: BlattWeisskopf
Each of these cases has been taken from
:cite:`chungPartialWaveAnalysis1995`, p. 415. For a good overview of where
to use these Blatt-Weisskopf functions, see
:cite:`asnerDalitzPlotAnalysis2006`.
See also :ref:`usage/dynamics/lineshapes:Form factor`.
"""
@property
def q(self) -> sp.Symbol:
"""Break-up momentum."""
return self.args[0]
@property
def d(self) -> sp.Symbol:
"""Impact parameter, also called meson radius."""
return self.args[1]
@property
def angular_momentum(self) -> sp.Symbol:
return self.args[2]
def evaluate(self) -> sp.Expr:
angular_momentum = self.angular_momentum
z = (self.q * self.d) ** 2
return sp.sqrt(
sp.Piecewise(
(
1,
sp.Eq(angular_momentum, 0),
),
(
2 * z / (z + 1),
sp.Eq(angular_momentum, 1),
),
(
13 * z ** 2 / ((z - 3) * (z - 3) + 9 * z),
sp.Eq(angular_momentum, 2),
),
(
(
277
* z ** 3
/ (
z * (z - 15) * (z - 15)
+ 9 * (2 * z - 5) * (2 * z - 5)
)
),
sp.Eq(angular_momentum, 3),
),
(
(
12746
* z ** 4
/ (
(z ** 2 - 45 * z + 105) * (z ** 2 - 45 * z + 105)
+ 25 * z * (2 * z - 21) * (2 * z - 21)
)
),
sp.Eq(angular_momentum, 4),
),
)
)
def _latex(self, printer: LatexPrinter, *args: Any) -> str:
l, q = tuple(map(printer._print, (self.angular_momentum, self.q)))
return fR"B_{l}\left({q}\right)"
[docs]def relativistic_breit_wigner(
mass: sp.Symbol, mass0: sp.Symbol, gamma0: sp.Symbol
) -> sp.Expr:
"""Relativistic Breit-Wigner lineshape.
.. glue:math:: relativistic_breit_wigner
:label: relativistic_breit_wigner
See :ref:`usage/dynamics/lineshapes:_Without_ form factor` and
:cite:`asnerDalitzPlotAnalysis2006`.
"""
return gamma0 * mass0 / (mass0 ** 2 - mass ** 2 - gamma0 * mass0 * sp.I)
[docs]def relativistic_breit_wigner_with_ff( # pylint: disable=too-many-arguments
mass: sp.Symbol,
mass0: sp.Symbol,
gamma0: sp.Symbol,
m_a: sp.Symbol,
m_b: sp.Symbol,
angular_momentum: sp.Symbol,
meson_radius: sp.Symbol,
) -> sp.Expr:
"""Relativistic Breit-Wigner with `.BlattWeisskopf` factor.
For :math:`L=0`, this lineshape has the following form:
.. glue:math:: relativistic_breit_wigner_with_ff
:label: relativistic_breit_wigner_with_ff
See :ref:`usage/dynamics/lineshapes:_With_ form factor` and
:cite:`asnerDalitzPlotAnalysis2006`.
"""
q = breakup_momentum(mass, m_a, m_b)
q0 = breakup_momentum(mass0, m_a, m_b)
ff = BlattWeisskopf(q, meson_radius, angular_momentum)
ff0 = BlattWeisskopf(q0, meson_radius, angular_momentum)
mass_dependent_width = gamma0 * (mass0 / mass) * (ff ** 2 / ff0 ** 2)
mass_dependent_width = mass_dependent_width * (q / q0)
return (mass0 * gamma0 * ff) / (
mass0 ** 2 - mass ** 2 - mass_dependent_width * mass0 * sp.I
)
[docs]def breakup_momentum(
m_r: sp.Symbol, m_a: sp.Symbol, m_b: sp.Symbol
) -> sp.Expr:
return sp.sqrt(
(m_r ** 2 - (m_a + m_b) ** 2)
* (m_r ** 2 - (m_a - m_b) ** 2)
/ (4 * m_r ** 2)
)