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This shows the tree-like hierarchy of Monte Carlo Particles (MCParticles) in the event. A particles "children" can be viewed by expanding it using the "+" button.
More detailed information on MCParticles is available from the MCParticles collection, which has one record for every particle in the event.
From this table, you can see the type, energy, momentum, start and ending points, etc. of each particle.
Calorimeter Hit Collections
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