Very early this morning we got the first lead-lead collisions at the LHC! I am all a twitter. This is a very exciting time. I just arrived at CERN today and I am very, very jet-lagged, so I’ll keep this short.
Pictures. What you all want to see is pictures.
Here are some event displays with the first Pb+Pb collisions seen by ALICE. This is an example:
These event displays only show information with the Inner Tracking System (ITS). Our main tracking detector, the Time Projection Chamber (TPC), was off for these collisions. The reason is that the beams were not perfectly stable for the first collisions and we did not want to damage our TPC.
And check out this video of an event display (the original video is here):
And now that we have lead-lead data, we have a lot of work to do. Expect the first lead-lead paper soon. It will be a multiplicity paper like ALICE’s first few proton-proton papers. We will just measure the number of charged particles in an event. This information alone will tell us a lot about heavy ion collisions – the first estimates for how many particles we should see in an event varied by a factor of 4, from 2000-8000 tracks.