First lead-ion collisions in the LHC
Update 8:20 a.m. EST November 8: CERN just issued a press release announcing the successful smashing of lead ions in the LHC, and the text and images below have been updated to including information from the first run of lead-ion collisions with stable beams.
The Large Hadron Collider smashed its first lead ions Sunday, November 7 at around 12:30 a.m. Central European Time. The first collisions in the center of the ALICE, ATLAS and CMS collisions took place less than 72 hours after the LHC ended its first run of protons and switched to accelerating lead-ion beams.
The lead-ion collisions take place at an energy of 287 TeV per beam. Why the much higher energy compared to the LHC's 3.5 TeV proton 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.
The first event display shown here was collected by the ALICE experiment during the very first collisions early Sunday morning. 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.
Sunday's very first collisions were recorded by only part of the ALICE, ATLAS and CMS detectors. For example, the first event display shown here only contains information from ALICE's innermost detector system. ALICE's main system for tracking particles was not switched on for these very first collisions, as the team operating the LHC accelerator had not yet declared "stable beams." The teams operating the LHC experiments only switch on their most sensitive detection equipment when the accelerator team declares stable beams, indicating that the accelerator operators have finished making major adjustments to the beams' trajectory.
The first collisions with stable beams took place at 11:20 a.m. Central European Time on Monday, November 8. The next three images displayed here show lead-ion collisions in the ALICE, ATLAS and CMS experiments with their full detectors switched on and recording data.
The LHC will collide lead ions until December 6. The accelerator will then shut down for two months for maintenance, and will start up again in February with proton beams.
Thanks to Christine Nattrass from the US LHC Blogs for the pointer to the first images and video from ALICE.