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Ken Bloom | USLHC | USA

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LHC: Play along at home! (or, scoreboard watching)

OK, I’ll admit it — instead of writing blog posts or reviewing results that are headed for ICHEP or doing something else productive, I find myself all too easily distracted by information on the current status of the LHC. As the gallant accelerator physicists work to push the machine to higher beam intensities and collision rates, I’m eager to learn about each little bit of progress. It definitely has some meaning to me — the more collisions the LHC produces, the more the experiments can record, and the greater the chance that we will see any particular physics process take place. Especially as we get close to the big ICHEP conference, we are all curious about how much data we might record before then, because that will determine what measurements might possibly be ready. (Of course it’s also determined by how quickly we can push the data through data analyses, how well we can understand detector performance and so forth; let’s not put all of the burden on the LHC.)

It’s not like I can do anything to make the luminosity go up, but I feel better (or at least distracted) by knowing what’s going on at this minute. This is akin to scoreboard watching in baseball, where the outfielders in one game might have their eye on the scoreboard above them to see how the competition is doing. (In fact, back at the Cornell Electron Storage Ring, the display that showed the luminosity numbers for the past 24 hours was called the “scoreboard”, so the analogy fits.)

So, if you want to play along at home, here are a few Web pages you can keep an eye on. Some of these have been mentioned in previous posts on this blog, but it’s been a little while and I’ll give a few more details.

To know what’s happening right now, check out LHC Page 1, which gives the current machine status and the (very) short-term running plan. Here you’ll typically see plots of the amount of beam current and the beam energy in the LHC, and, during periods of collisions for “physics” (i.e. data-taking by the experiment as opposed to studies of collisions done to optimize machine performance) there will be plots of the observed instantaneous luminosity reported by each of the four experiments. (Instantaneous luminosity is a measure of collision rate; its units of inverse centimeter squared per second deserve explanation in a second post.) The experiment reports can also be seen on the LHC Operation page. At other times, it will show the status of preparing to go to collisions, such as “ramp” (increasing beam energy to 3.5 TeV) or “squeeze” (focusing the beams to increase the collision rate). There are also helpful short messages about what’s going on, such as “this fill for physics” or the somewhat unnerving “experts have been called.”

The medium term run plan can be seen on the LHC Coordination screen. Here you can see the goals for the coming week, what administrative limits are currently in place to protect the machine, and the planned activities for the next few shifts.

While the collision rate is interesting, what really counts is the “integrated luminosity”, or the total number of collisions that have taken place. Up-to-date charts can be found here; the data go back to March 30, the start of 3.5 TeV operations. You can see here that the integrated luminosity has been increasing exponentially in time (when the LHC is not in studies periods or technical stops). If the collision rate were the same all the time, the integral would only increase linearly, so this demonstrates just how quickly the LHC physicists are figuring out how to make the machine go.

That’s what I’ve been keeping an eye on. OK, all of you stop looking at Facebook, and distract yourselves with the LHC instead!

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