Calculation of the section of the $2\to 4$ cascade reaction by the basis spinor method

A general technique for calculating cascade processes in the framework of narrow resonances' improved approximation is considered. Possible experimental restrictions on the emission angles of final and intermediate particles were taken into account. An important distinguishing feature of the technique is the usage of the Poincaré-invariant helicities for the final particles of the cascade reaction, as well as the method of basis spinors. As a result, the section of the cascade process $ab\to cd\to 12+34$ has a compact form.