Lead-lead collisions start at the LHC after 5 years

Picked one by one from a mixed channel. Transcript check: Scientist explains the physics and purpose of lead-ion collisions and quark-gluon plasma research at the LHC.. Channel rule: Include only explainer videos and series that teach how particle physics or CERN's accelerators and detectors work (e.g. 'Particle Collisions', 'The Higgs Discovery Explained', 'What is the Higgs boson?', 'LHC animation: The path of the protons') and full-length science documentaries such as 'Hunting for Neutrinos' and 'Particle Hunters'; exclude news or result announcements, anniversaries, event recordings, trailers and teasers, promo overviews and music or art pieces.