The Large Hadron Collider has succeeded in colliding lead nuclei at a centre of mass energy of 574 TeV. That is by far the highest energy collisions ever seen in any particle accelerator exceeding previous records of the RHIC collider by a factor of 14.
The process of commissioning heavy Ion collisions at the CERN accelerator started less than three days ago so the speed with which they have started collisions is impressive. In fact the physical process of colliding heavy ions is almost identical to colliding protons. The lead nucleus has a charge of exactly 82 times the charge on a proton, but the curvature of a particle in a magnetic field depends only on the ratio of charge to energy. So if the lead ions are accelerated to exactly 82 times the energy of the protons they will follow the same path and the setup used to collide protons works just as well for ions.
The luminosities used last night were just a fraction of the records set with proton collisions a few days ago, but the lead ions have a larger cross-section so some interesting data may already have been collected in last night’s run which lasted three hours. Two bunches per beams were used to provide collisions in CMS, ATLAS and ALICE, but it is the ALICE detector that is best suited to studying the showers of thousands of particles that these collisions produce.
Here is a simulated picture of a collision in ALICE. Hopefully some real pictures will be available soon. Update: they are, see below.
Update: Collisions have been underway again this afternoon. Here is a picture of a collision from CMS. This was taken from the Live CMS fireworks display.
And another 3D picture from CMS
Here is a superb animation of a 3D recording of one of the first Heavy Ion events seen today in ALICE
More pictures from ALICE are here