Insert form factors in TR-013 (spin alignment)

[redeboer]

TR-013 by ComPWA/compwa.github.io#111 differs from 10.1155/2020/6674595 in two ways:

• It uses Breit-Wigners without form factors. Since Implement switches for configuring coefficient names ampform#251 however, it's possible to generate 'helicity-like coefficient names' for an amplitude model generated with formalism="canonical-helicity". This makes it possible to generate all LS-combinations and generate the coefficients from Table 1.
• It uses coefficients for the amplitude of the each decay chain, not helicity couplings. See Split amplitude coefficients into two-body-decay coefficients ampform#254. Note that the difficulty here lies in correctly correlating the helicity couplings as described in Appendix D.

[redeboer]

PR ComPWA/compwa.github.io#125 currently seems to illustrate the second point: the introduction of form factors results in a completely different ratio for each of the distributions per topology. This may be the consequence of setting 'amplitude coefficients' rather than helicity couplings.

New (after ComPWA/compwa.github.io#125, with form factors)

Old (before ComPWA/compwa.github.io#125)