Available Decay Model

2-body decays

1. "gls-bf", "default" (HelicityDecay)

default decay model

The total amplitude is

\[A = H_{\lambda_{B},\lambda_{C}}^{A \rightarrow B+C} D^{J_A*}_{\lambda_{A}, \lambda_{B}-\lambda_{C}} (\varphi,\theta,0)\]

The helicity coupling is

\[H_{\lambda_{B},\lambda_{C}}^{A \rightarrow B+C} = \sum_{ls} g_{ls} \sqrt{\frac{2l+1}{2 J_{A}+1}} \langle l 0; s \delta|J_{A} \delta\rangle \langle J_{B} \lambda_{B} ;J_{C} -\lambda_{C} | s \delta \rangle q^{l} B_{l}'(q, q_0, d)\]

The fit parameters is \(g_{ls}\)

There are some options

(1). has_bprime=False will remove the \(B_{l}'(q, q_0, d)\) part.

(2). has_barrier_factor=False will remove the \(q^{l} B_{l}'(q, q_0, d)\) part.

(3). barrier_factor_norm=True will replace \(q^l\) with \((q/q_{0})^l\)

(4). below_threshold=True will replace the mass used to calculate \(q_0\) with

\[m_0^{eff} = m^{min} + \frac{m^{max} - m^{min}}{2}(1+tanh \frac{m_0 - \frac{m^{max} + m^{min}}{2}}{m^{max} - m^{min}})\]

(5). l_list=[l1, l2] and ls_list=[[l1, s1], [l2, s2]] options give the list of all possible LS used in the decay.

2. "helicity_full" (HelicityDecayNP)

   Full helicity amplitude

   \[A = H_{m_1, m_2} D_{m_0, m_1-m_2}^{J_0 *}(\varphi, \theta,0)\]

   fit parameters is \(H_{m_1, m_2}\).

3. "helicity_parity" (HelicityDecayP)

   \[H_{- m1, - m2} = P_0 P_1 P_2 (-1)^{J_1 + J_2 - J_0} H_{m1, m2}\]

4. "gls-cpv" (HelicityDecayCPV)

   decay model for CPV