CLAS12 Analysis¶

HIPO is the native data format for the CLAS12 experiment at Jefferson Lab. The reconstructed output of the CLAS12 chain is a collection of REC::* banks per event — REC::Particle for the particle list, plus detector-level banks (REC::Calorimeter, REC::Scintillator, REC::Cherenkov, REC::Track, REC::Traj, …) that link back to particles via a pindex column.

This section covers the patterns you actually use to do physics on CLAS12 HIPO files. It is narrower and more opinionated than the generic Recipes section — if you're writing your first CLAS12 analysis, start here.

Pages¶

• First analysis — the minimum viable CLAS12 loop: open a file, iterate events, filter charged tracks, histogram the vertex-z. Builds on the quickstart but with CLAS12-specific PID / status / charge conventions.
• The REC:: bank family — a tour of the banks CLAS12 reconstruction writes: what REC::Particle contains, what the per-detector banks are for, and which columns you'll reach for most often.
• Cross-bank linking via pindex — the single most important idiom in CLAS12 analysis: every detector-level bank carries a pindex column pointing back to the particle row it belongs to. Walk through joining REC::Particle with REC::Calorimeter using getRowListLinked().

Prerequisites¶

You should already be comfortable with the material in:

• Getting Started — building and linking against hipo4.
• Recipes: reading files and Recipes: row filtering — the generic HIPO idioms the CLAS12 patterns are built on.

CLAS12 particle codes quick reference¶

CLAS12 uses the standard PDG Monte-Carlo numbering scheme in the pid column of REC::Particle. The ones you will see most often:

The full PDG table is at https://pdg.lbl.gov/. CLAS12 reconstruction assigns these based on calorimeter response, time-of-flight, Cherenkov, and tracking — the per-particle confidence lives in the chi2pid column, and the detector combination is encoded in status (see The REC:: bank family).