First direct observation of a phenomenon known as jet quenching in quark–gluon plasma. The main significance is that its observability will enable more detailed study of the behaviour of material in this extreme state.

Quarks and gluons are the particles out of which protons and neutrons are made. Protons and neutrons form the nucleus of any atom—the heavy part in the centre, surrounded by a cloud of electrons. Quark–gluon plasma is a state in which conditions are so extreme that the quarks and gluons can move freely instead of being grouped together into protons and neutrons.