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Ken Bloom | USLHC | USA

View Blog | Read Bio

It’s a wrap: proton Run 1 ends

On Monday at 6 AM CERN time, the LHC ended its collisions of protons for 2012, and in fact until 2015, when the “long shutdown” for energy upgrades is completed. [There will be heavy-ion collisions in early 2013, but the details are beyond my expertise.] Here’s what appeared on the LHC status screen:

It’s the end of an era for the LHC, the end of what we might someday call “Run 1”, the period of first beams at (relatively) low energies, when we got our first glimpse of a new energy scale, and gathered just enough data to see the first glimmerings of (maybe) the Higgs boson. Considering how long we waited for the start of Run 1 — nearly twenty years from the first concepts for the the LHC and its detectors — it is rather amazing that we’re now at the end of the run, after a mere three years.

Still, it’s been a great three years. Here is the plot that captures the whole story:

LHC integrated luminosity summary

This is the integrated luminosity recorded by CMS, essentially the number of collisions that the experiment observed, year by year. Remember all the excitement of the first data in 2010? That turned out to be a tiny amount of data compared to what we have recorded since; while we made very good use of it at the time, it was just hinting at the future success of the LHC. And even after the great advances in 2011, by the start of June 2012 we had recorded more data this year than we had in all of last year. Once again, all the experimenters thank the LHC team for the excellent performance of this still new machine.

The last few days of the proton run were spent looking towards the future. Since there won’t be any more proton collisions for two years, it’s important to do some tests that can guide our thinking about how to operate the LHC in 2015. So far, the LHC has run with “50 ns bunch spacing”; that is, the minimum time between bunch crossing is 50 nanoseconds. (Remember, the LHC beam is not continuous, but “bunched”, with a large number of protons close together in the beam, followed by a 50-foot gap before the next bunch in the beam.) This week, the LHC experimented with 25 ns bunch spacing, and even allowed the experiments to take a little bit of data in this mode on Saturday night and Sunday morning. Obviously, with the shorter bunch spacing, you can have beam collisions happening twice as often, and that means that you could potentially achieve the same total number of collisions with fewer protons per bunch. That’s good for the experiments, as each event that we record will have fewer collisions in it, making it easier for us to reconstruct what went on. With 25 ns spacing, we’d probably need less computing capacity and calibration and the like would be easier. But from the accelerator perspective, it is easier to operate the LHC with 50 ns spacing, and the machine operators can’t guarantee that they could provide as much integrated luminosity at 25 ns spacing as the could with 50 ns. Thus, it was important to take some time to understand how to operate the LHC this way. It’s ultimately up to the LHC managers to decide what the best mode for operations is. From the experiment side, it would be easier for us to have 25 ns spacing, but we wouldn’t want to do that at the cost of less data, and perhaps missing a chance of a discovery as a results.

Meanwhile, what does a 3000-member collaboration do with itself when there is no data to record? (Besides sending and reading email.) Quite a lot. First, there are a number of upgrades, repairs and improvements to be made on the detector in the next two years. There is a carefully choreographed dance to be performed in the collision hall, where the CMS detector must be opened up for access to the different components, and the schedule for all the work to be done could be pretty tight. There are also preparations to be made for how we analyze the data in 2015. The environment will be a lot like in 2010: we’ll be at a new beam energy, and in a physics environment that we’ve never seen before, so we’ll have to be ready for anything that might appear in the data. And we will continue our studies of the fabulous three years of data already recorded. During the past three years, the collaborations have released multiple papers on particular topics, with increases in the amounts of data analyzed each time and improvements in analysis techniques. But the next round of papers will use the full dataset, and there won’t be any “next” papers. The analysis techniques then must be the best possible; there won’t be another shot for improvements, as the next word will be the final word, at least until 2015. This too will take a lot of effort from the scientists.

Congratulations to everyone on a successful Run 1, and let’s look ahead to a busy shutdown and an exciting Run 2 beyond!

  • roger

    Congrats on all the data – i’m anxious to hear about the papers using the full 21.5+fb of recorded data!

    BTW, i remember seeing a publicly accessible outline of the planned LHC upgrades but I can’t find it anymore. Will ‘2015’ be starting in March like normal years or will the upgrades actually be finished much later in 2015 meaning that 2015 may be like another 2010 for the amount of real data collected?

  • Ken Bloom

    Honestly, I think it’s too early to say what the 2015 schedule will be, although I am expecting it will be a standard sort of CERN year, with collisions not starting on January 2 but more like March as you say. In terms of the amount of data…the LHC will be a new machine again, but not as new as in 2010, so I would guess more data than we got that year, but maybe not as much as we got this year. Any amount of data at 13 TeV will be useful, though!

  • Ken Bloom

    Also, the official CERN end-of-run press release is at


    and they have a nice brief description of 25 ns bunch spacing there.

  • Xezlec

    Cool. Best of luck with all the in-depth analyses of that massive pile of data. Sounds like you’ve got your work cut out for you!

  • NBorders

    Thanks for the post. I love reading these blogs from time to time. I was unaware that there would be a 2 year pause on any testing. Makes sense.

    Another thing to look forward to.

    Keep posting!


  • I think since there was not much anticipation about the fact that the machine can work well in a 25 ns mode..that Particular improvement to the nature of operations was not on the cards till last week as one can Predict..

    But since it is now on the agenda it’ll certainly take some extra time..3 months or so more which I think I read also somewhere..probably that was in Guardian !!! So it’s May or Early June 2015..though like everyone else interested in the stuffs happening there, I also want the operations to start much earlier..but we are helpless..aren’t we ??