• After a purchase — the trial or the unlock — TreeLevel opens at once, without having to leave the app and come back.

FREE TO TRY • TreeLevel is free to download and to try for 14 days, everything included. • Then a single purchase unlocks everything, with no time limit, on Mac and iPad, shared with your family. • Bought TreeLevel before this version? Nothing changes for you: everything stays unlocked. ONE SELECTION FOR THE MACHINE SOURCE • The same selection holds for every phenomenon — acceptance, a visible object above a threshold, visible mass between leptons — and defines the fiducial cross section shown. The generation thresholds follow from it. • Two options, off by default: dressed leptons (nearby photons given back to the lepton, as ATLAS and CMS do) and quark flavour from the jets (b or c).

THE DETECTOR IN 3D • A 3D view of the detector and the event: turn it, zoom, choose what it shows. • Endcaps close the barrels, with the beam hole, inside or outside for each calorimeter. • A Show menu in every enlarged view: each part of the detector and of the event, the incoming particles, a grid. DOWN TO THE INTERACTION ZONE • Zoom up to ten quadrillion times: from the metre of the detector to the femtometre. • With Pythia, the zone where the collision took place: the parton shower, the body of the colour strings and the hadrons born from them, in cross-section and in 3D — the generator's model, nothing measured. • The crosshair brings the collision back to the centre and follows it from one event to the next. ALSO • Past jobs: restore the settings of an earlier job to run a generation again. • The preset detectors carry their name in your language.

PYTHIA 8 ON IPAD • A module downloaded from within the app (14 MB; 55 more for hadrons): Pythia 8.318 in WebAssembly, free software under the GPL. Events come out showered, hadronised and decayed. • The Machine source: two beams and an energy, what the experiment records — everything the detector sees, or one phenomenon — and the cross section measured by counting. TWO NEW SPACES • Generation: thousands of unweighted events, one at a time or in histograms, with selections and error bars; export and import in Les Houches and HepMC3. • Detector: coaxial cylinders, calorimeters, anti-kT jets, missing energy; the event's cross-sections, the reconstructed objects, the performance over the sample. THE FILTER • Step only through the events that meet your criteria: hard process, electrons, muons, photons, τ, jets, missing energy, pair mass. Histograms and selection follow the filter. THE DETECTOR UP CLOSE • The enlarged detector view: pinch to zoom up to a trillion times, with a scale bar; trajectories start from their real vertices. • Tap a trajectory to see what it is, where it comes from and what it produced. AND ALSO • A sample showered elsewhere — a HepMC3 file from Pythia, Herwig or TreeLevel for Mac — opens here, right through to the detector. • Spin 3/2: the Δ resonance and the Ω⁻ in the hadron model, with two new examples.