By the most radiant sunny Easter Sunday, sixteen of us are in the ATLAS control room, keeping an eye on several dozens computer screens while the Large Hadron Collider (LHC) is breaking one record after another.
It’s been an amazing weekend, with new records being established at each new fill. First of all, around midnight on Thursday, April 22, the LHC set a new world record for beam intensity at a hadron collider when it collided beams with a luminosity of 4.67 x 1032cm-2s-1, exceeding the previous world record of 4.024 x 1032cm-2s-1 set by the Tevatron in 2010. What was most amazing is that at each new fill, it got even better.
Our team has been on shift for the last three days. It’s a great crew, with people coming from Malaysia, Ukraine, Russia, Japan, Canada, USA, Pakistan, UK, Portugal, Italy, China and the Czech Republic. Being shift leader, I get to talk with everybody, so it’s a lot of fun.
Every time we came on shift at 15:00, the leaving crew bragged about having witnessed a new record: highest intensity for the beams (that’s how many protons were circulating in the accelerator), or highest luminosity (how many collisions created per second) and now, highest data sample collected during one fill. But we got our chance to do just the same at 23:00 when our replacements came in!
Following ten days of down time dedicated to an intensive scrubbing period to allow pushing the machine higher than ever, it’s been one successful fill after another. Well… there have been a couple aborted attempts but that’s part of the game. It takes about three to four hours to fill up the accelerator with fresh beams, accelerate them at full energy then bring them into collisions. Meanwhile, in the four LHC detector control rooms for ALICE, ATLAS, CMS and LHCb, the four large experiments collecting collision data from the accelerator, we are following each step, waiting for the safe moment where we can turn on the innermost layers of our detectors and start recording the proton collisions. The last run started around noon on Saturday and ended 16 hours later at 6:00 am this morning. During this time, ATLAS and CMS collected about 24 inverse picobarn of data. Well, pico might not seem much to you since it is one millionth of a millionth of that weird unit of a barn, but to put it in perspective, compare that to the 45 inverse picobarns total we got during the whole of last year! Yes, that means, the best of a year with 15-20 people on shift, 24 hours a day, waiting to collect this data. A huge effort, so we are thrilled to see the data coming in at a much-increased rate now.
At the very start of the LHC in March 2010, we were keeping records of the data taken in units of inverse nanobarns, that is measuring it in units one thousand times smaller. So in the course of only one year of operation, we went from counting each inverse nanobarns we received to using inverse picobarns, and very soon, we will be estimating our data sample in femtobarns, a unit a million times bigger. Already this year, we have more than doubled what we had last year and we should reach one inverse femtobarn in the next couple of months.
So this has been a great way to spend the Easter weekend, with lots of data collected, not to mention a very sizeable crop of Easter eggs too!
Pauline Gagnon
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