Decay finder algorithm for reconstructed particles in Run III at the \lhcb experiment

The \lhcb software is being adapted to tackle the challenges associated with the Run III of \lhc. As a result, a vectorised reconstruction event model is planned to be introduced for parallel processing of Run III data. As a consequence, the software used for offline processing of data is also being updated. Shipped as part of the new suit of upgrades is a new decay finder algorithm. This algorithm improves upon the old ones used in the Run I/II periods, particularly in handling of identical particles and improvements with added flexibility in the syntax of the user-specified decay descriptors. The structure of the new decay finder, which includes templated functions, makes it agnostic towards the type of the input particle. It is designed in-line with modern software practices through systematic implementation of unit tests and detailed documentation/comments to ensure good coverage of the features and code maintainability.