Charmed Λ Baryon Decays (LHCb)

The PPSS (Programme for Polish Summer Studentships) placed this project inside the LHCb collaboration's charm-physics effort, under Prof. Dr hab. Mariusz Witek at IFJ PAN in Kraków — one of LHCb's home institutes and a major contributor to the experiment's tracking and physics-analysis software.

Charmed Λ baryon decays are a useful probe of both the strong-interaction dynamics that bind quarks into baryons and, in some channels, of CP violation in the charm sector — but the genuine signal sits under a large combinatorial background from unrelated tracks that happen to reconstruct into a similar invariant mass. Separating the two by hand-tuned cuts alone leaves signal on the table; a multivariate classifier does better.

The core of the project was building and validating a Boosted Decision Tree (via XGBoost) trained on kinematic and vertex-quality variables from ROOT ntuples, to assign each candidate decay a signal-likeness score rather than a hard pass/fail cut — the standard approach for squeezing more usable signal out of LHCb data without inflating the background.