The Large Hadron Collider Accelerates

Every time I turn around, the Large Hadron Collider [LHC] is breaking another record. Since 2012 data-taking began April 5th, the news has been improving steadily and rapidly.  Over the weekend, the accelerator physicists brought proton-proton collision rates — the total number of collisions per second — back up to the same level as last year’s record, and even a bit beyond.  The LHC produced over these two days more than six times as much data as was obtained in all of 2010, and a quarter of what was obtained in the first three months of 2011.  Granted, the accelerator physicists won’t keep up this torrid pace every day; there are times (typically weekends and overnights) where the LHC produces lots of data, and other times where the focus is on improving the accelerator and much less data is gathered.  But so far the signs are very good indeed.  Some experts were unsure whether the move from 7 TeV to 8 TeV energy per collision would be smooth, but fortunately it seems that the accelerator is performing very well at the new energy.

Two differences from last year that are important to know:

• The energy per collision is higher:  8 TeV of energy for each proton-proton collision, rather than 7 TeV last year.
• The simultaneous collision rate (or “pile-up”) is higher: the current high collision rate per second is being obtained with a smaller number of bunches of protons per beam than at the end of last year, by about 25%, which means the number of simultaneous collisions has gone up by about 25%, to as many as 30 collisions or so happening at virtually the same instant.  (Pile-up will be a recurrent theme (and perhaps thorn) in 2012.)  But the use of fewer bunches at the present time means that more bunches can be added later, which will allow another increase in the collision rate per second sometime this year (I’m not sure when.)

The challenges ahead for the ATLAS and CMS experiments to handle this firehose of data, especially the pile-up, are not to be minimized.  I’ve written about one of the big challenges here; there are others.  But better to have to face these difficulties than to be sitting idly, twiddling their thumbs and waiting for data to start showing up!   Also, the more data they get in the early part of 2012, the sooner Phase 1 of the search for the Higgs particle will come to a close — and the more likely that July 2012 will see significant news, perhaps fairly convincing news, concerning the hint of a Higgs particle with a mass of about 125 GeV/c².