B-physics trigger: update fit procedure for cascade decays of the B_c+
This MR introduces a new approach for the cascade decays of B_c+:
- B_c+ -> J/psi(-> mu+ mu-) D_s+(->phi(-> K+ K-) pi+)
- B_c+ -> J/psi(-> mu+ mu-) D+(-> K- pi+ pi+) now are
There is no possibility to run cascade vertex fitter at HLT level due to the CPU limitations. So that, three tracks from D+/D_s+ are fitted to the standalone secondary vertex. The combined momentum of D+/D_s+ candidate is constrained to point to the dimuon vertex. We found that simplified approach is efficient enough to select requested decay topologies.