There were collisions at injection energy (900 GeV), including higher intensity / more bunches. There were collisions at higher energy (2.36 TeV), making the LHC the highest energy man-made particle collider ever!
I'm mostly surprised and amazed by how well the ATLAS detector performed. Sure, my collaborators have been preparing for this for years, but I was cynical as anyone about how well we would do under pressure... LHC beams injected, now colliding, now "stable beams", go! I think we surpassed many expectations. And we collected a lot of data!
The fun part now is combing through those runs and cherry picking the best ones. We call this "data quality", and though the term becomes jargon within the collaboration, its meaning is important. We ask basic questions like What were the LHC conditions? Were all of the detectors on and functioning properly? Were we reading out the data? Was the magnetic field on? How about the other one? (on ATLAS we have a solenoid and the famous toroids with the orange stripes...)
I've really been looking forward to this Christmas shutdown. So, it may seem kind of nerdy, but although many of my fellow collaborators will head home for some much-needed vaca with their fams, I will be hanging around my apartment in Saint Genis, analyzing this early data. I'll be looking at indicators of data quality and trying to extract some physics. (Don't worry, I'll take some time off to celebrate Christmas and New Years' with friends.) And I'm really excited to be rid of the meetings and distractions for 2 whole weeks!
Perhaps it's a bit cheesy, but I have this great feeling that I am living the dream right now. As a grad student on BaBar, I desperately wanted to be a postdoc at CERN, on an LHC experiment, for the startup of the new greatest collider in the world. I pushed really hard my last year to finish my thesis and get out in time so I wouldn't miss all of the fun :) Delays aside, here I am! The night we got the first stable collisions I was sitting at Point 1 until 3am, eagerly marking every LHC bunch injection. The beam intensity went up by steps, closely followed by my enthusiasm. The Liquid Argon Calorimeter performed beautifully, calmly collecting data as if it was no big deal; it was built for high energy collisions, not cosmics! This is what I got into physics for, this thrill. It's awesome, and there's a lot more to come next year.
Happy Holidays to you and yours. I leave you with the LHC, signing off: