to occur. The LHC, with a centre-of-mass energy around 5.5 TeV/nucleon, will push the energy reach even further. During head-on collisions of lead ions at the LHC, hundreds of protons and neutrons smash into one another at energies of upwards of a few TeVs. Lead ions are accelerated to more than 99.9999% of the speed of light and collisions at the LHC are 100 times more energetic than those of protons - heating up matter in the interaction point to a temperature almost 100,000 times higher than the temperature in the core of the sun. When the two lead nuclei slam into each other, matter undergoes a transition to form for a brief instant a droplet of primordial matter, the so-called quark–gluon plasma which is believed to have filled the universe a few microseconds after the Big Bang. The quark–gluon plasma is formed as protons and neutrons "melt" into their elementary constituents, quarks and gluons become asymptotically free. The droplet of QGP instantly cools, and the individual quarks and gluons (collectively called partons) recombine into a blizzard of ordinary matter that speeds away in all directions. The debris contains particles such as pions and kaons, which are made of a quark and an antiquark; protons and neutrons, made of three quarks; and even copious antiprotons and antineutrons, which may combine to form the nuclei of antiatoms as heavy as helium. Much can be learned by studying the distribution and energy of this debris. First lead-lead collisions The Large Hadron Collider smashed its first lead ions in 2010, on 7 November at around 12:30 a.m. CET. The first collisions in the center of the ALICE, ATLAS and CMS detectors took place less than 72 hours after the LHC ended its first run of protons and switched to accelerating lead-ion beams. Each lead nucleus contains 82 protons, and the LHC accelerates each proton to an energy of 3.5 TeV, thus resulting in an energy of 287 TeV per beam, or a total collision energy of 574 TeV. Up to 3,000 charged particles were emitted from each collision, shown here as lines radiating from the collision point. The colors of the lines indicate how much energy each particle carried away from the collision. Proton-lead collisions at the LHC In 2013, the LHC collided protons with lead ions for the LHC's first physics beams of 2013. The experiment was conducted by counter-rotating beams of