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Panels and the 3-D scene

The four panels

The layout of the original matplotlib figure, for slides and papers.

(a) r-φ, whole event — track helices, EM showers as towers of length proportional to energy, and the HPC radius taken from the shower positions themselves (a dashed circle at r ≈ 2.14 m).

(b) r-z — the same tracks, with r signed by which thrust hemisphere the track's momentum points into, so the two jets separate.

(c) vertex detector, r-φ — the three VD layers, their radii clustered out of the hits (62.5, 87.8, 106.5 mm in the reference event), the R-φ hits, the primary vertex and the accepted AABTAG secondary vertices. The matplotlib version needed a fixed inset for the vertex region; here you zoom with the mouse, which is the one place interactivity pays for itself immediately.

(d) RICH — Cherenkov angle against momentum for chosen tracks, liquid and gas radiators, with the expected π/K/p curves (n_liq 1.2718, n_gas 1.0019; gas thresholds π 2.26, K 8.0, p 15.2 GeV). A track above the pion threshold with zero gas photons is drawn as a veto marker (▼), because that absence is a measurement, not missing data.

The 3-D scene

The layout a general-purpose event display uses: the VD layers and HPC as translucent barrels, the helices in space, showers as towers pointing outward, vertices as markers, and the beam line.

scene.aspectmode="data" keeps it physically proportional, which is why the 2.1 m barrel dwarfs the vertex region — that ratio is real, and stretching it would be a lie about the detector.

A VD hit is not a point in space

A type-0 (R-φ) strip measures R and φ but not z; a type-1 strip measures R and z but not φ. So in three dimensions a single hit constrains a line, not a dot.

  • A hit belonging to a track is drawn at the z its own track measures — a real quantity.
  • A hit belonging to no track is drawn as the line parallel to the beam that it actually constrains, not as an invented point.

What the interactivity adds

  • hover names each track: index, charge, momentum, VD hit count, which vertex it starts from
  • the legend switches whole classes of object off
  • zoom replaces the fixed inset in panel (c)
  • selecting a collection dims everything that did not come from it

Both views carry

The DELPHI + EDM4hep mark, embedded as a data URI so it survives PNG/SVG export and an offline HTML file, anchored top-right — the subplot titles are left-aligned over their own panel, so a top-left mark lands on "(a) r-φ view".

No title and no run/event line are drawn into either figure: every number lives in layout.meta and the page renders it as live text.