Chamonix conference considers LHC running parameters

As the Large Hadron Collider once again cools down ready for its 2011 startup in February, the collider directorate are at Chamonix to discuss how they will operate in 2011 and beyond. The presentation slides for the 5 day meeting that started yesterday are being put online as the week progresses. Most of these are technical discussions of limited interest to an outsider but a couple at least are worth looking at.

The opening talk was about how the teams from the detector side saw the progress during 2010. The message is mixed with obvious pleasure that the main luminosity goal was exceeded at the end of the years run, but also some frustration at just how slow the build-up process was. For example they ask why 100/pb could not have been collected rather than 45/pb. In fact 100/pb could easily have been collected either by pushing the build-up of luminosity faster, or simply by doing more physics runs after the target luminosity was met. However, the beam directorate decided to use the time to try out bunch trains with shorter gaps between. This gave them valuable information about limitation factors that are essential to making the decisions about how to run the machine this year. However, the main message from the detectors seems to be that they would like things to move much quicker this year.

The most significant decisions that need to be made before the collider starts up are what energy to run at, and what bunch separation to use. The currently favoured energy for 2011 is 8TeV compared with 7TeV last year. This may not look like a big difference but in fact it provides a significant increase in production rates for heavy particles. For example, it will mean 40% more Top quarks produced. That will be very important because some of the most promising signals for new physics seen at the Tevatron require top production. The improvements in sensitivity for heavier SUSY particles is even better. A talk this evening on the LHC potential will give all the detailed analysis. That will be followed by other talks that consider the operational consequences and risks of running with energies of 8Tev, 9TeV or even 10 TeV, but the conclusion is likely to be that anything above 8 TeV is too risky.

How much luminosity will they collect next year? 1/fb is still the official target and 1/fb-3/fb is the official estimate, but some people are thinking optimistically about up to 5/fb . It depends on factors such as the bunch separation they will use. This is likely to be 75ns comapred to last year’s 150ns. 50ns was tried last year but found to produce too many side effects.

The next decision will be whether or not to continue the 2011 run into 2012. That would provide much more data, probably enough to get first postive observations of the Higgs sector. But the longer run would delay the upgrade to the full 14TeV. It would also make components more radioactive which is bad news for the engineers who have to carry out the upgrade. The directorate announced earlier that it was in favour of the longer run but the technicalities may get in the way. It’s a tough call.

Update 28-Jan-2011: With the Chamonix conference drawing to a close the proposal is that the LHC will run at 3.5TeV during 2011, not 4 TeV as hoped. However, the physics runs will continue into 2012 and it is hoped that after the normal end-of-year break they will be able to increase the energy for 2012 to “Hopefully higher than 4TeV”.

The 4TeV energy was seen as too much of a risk in exchange for the extra physics it will produce for 2011. Thermal amplifier development during 2011 could make the higher energies possible during 2012. The target integrated luminosity remains at 1/fb per experiment, but estimates put the actual figure at about 3/fb. This depends very much on how quickly they can recommission the beam and how efficiently they can run during the rest of the year.


16 Responses to Chamonix conference considers LHC running parameters

  1. […] This post was mentioned on Twitter by ComPod, Harpindon Groomsmill. Harpindon Groomsmill said: RT @ComPod Chamonix conference considers LHC running parameters 4 TeV? Viel mehr Bunches? U… […]

  2. […] The blog has turned out to be far more of a success than I ever expected when it was first started. There were few similar blogs back then, with Jacques Distler’s Musings having been around for a while, and Sean Carroll’s Preposterous Universe just starting up. Lubos Motl’s Reference Frame quickly followed, I gather somewhat in response to mine. These days, Musings seems to have gone dormant, but Sean and Lubos are still at it. I haven’t kept track of physics blogs in general, but there are now quite a few that deal with particle physics in one way or another. For particle phenomenology, Resonaances is a great source of information, for experimental HEP Tommaso Dorigo has a wonderful blog, and Philip Gibbs a viXra log does a great job of keeping track of the state of the LHC (for the latest, see here). […]

  3. […] can be downloaded here. For another summary of Chamonix you could read Philip Gibbs, “Chamonix conference considers LHC running parameters,” viXra log, January 25, […]

  4. Marcus says:

    Of course they will start to run full at power at end of 2012, that will trigger the end of world.
    Everything matchs..

  5. Luboš Motl says:

    I was just told that they will run at 2x 3.5 TeV only – but until 2012, roughly December 21th, when they invite a French-Mayan hybrid physicist, Dr Nostradamus, to play with the gadget before they turn everything off. 😉

  6. Bill K says:

    ¡Ay, caramba! This decision comes as a surprise. Way back last year when they decided to run at 3.5 TeV, a subsequent increase to either 4 or 4.5 was an integral part of the proposal. And much of the talk this year had, I thought, made a pretty convincing argument for the physics benefits of an increase. It began to sound like an increase to at least 4 TeV was almost guaranteed. But I guess it’s good that Steve Myers is being conservative.

    (What is a “thermal amplifier”? Something that might help reduce my heating bill?)

  7. Philip Gibbs says:

    I’m not sure how definitive the decision is to stay at 3.5 TeV. It just appeared as a proposal on the slides and they can always change their mind. The preceding summary talks had said there was no show-stopper for going to 4 TeV. The risks increased by a factor of 5 but were still small.

    I don’t know what a thermal amplifier is either, except that it obviously amplifies heat. I’ll have a guess the idea is that they will use something to detect the small heating in the splices during a quench so they can form better estimates of how likely a burnout is.

  8. […] de la operación del LHC). Más información sobre Chamonix 2011 en Philip Gibbs, “Chamonix conference considers LHC running parameters,” viXra log, 25-Jan-2011 (update 28-Jan-2011), Francis, “A summary of “Chamonix 2011 […]

  9. emulenews says:

    Bill, “thermal amplifier” is for best “Copper Stabilizer Continuity Measurements” CSCM (see slide 9 here).

    “The CSCM is a qualification tool that measures in situ the copper busbar resistance and thus can qualify a sector to the maximum current it can safely withstand. A typical bad joint has excess resistance of 2% – if they warm it up, its resistance grows by ~200 times – easy to detect!”

  10. Luboš Motl says:

    Dear Phil,
    the 3.5 TeV per beam in 2011 is official. If my word or even my blog is not reliable enough a source for you, try this one:


  11. Philip Gibbs says:

    It’s notable that they do not say what the energy for 2012 will be. They seem to be leaving open the option of increasing energy at end of 2011 as suggested at Chamonix.

  12. Bill K says:

    Don’t worry, by Chamonix 2012 everything will have changed again!

  13. Bill K says:

    I haven’t really been paying close attention to the ongoing saga of the LHC splices. So in academic tradition what that means is, I am assigned to find out everything I can about the subject and write it up! And no wonder for my confusion, the info is scattered in snippets among PDFs and PPT slides. It assumes you know all the jargon. And it all changes every few months anyway.
    But I have tried to stitch it together. The result is too long to include in a comment here, so I have posted it at

    • Philip Gibbs says:

      You have done your homework well and this is very useful. It explains more clearly why there could be a chance of increasing the energy for 2012 but there are a lots of “ifs” before that would be possible.

    • Lawrence B. Crowell says:

      This is a problem I have with LHC discussions. Beyond some of the ABCs I don’t know that much about accelerator physics. In reading this a lot of terms and strange units get thrown around. Sadly when I try to look up reading on the basics it is usually really basic material which if printed I would expect at a “gift shop.”

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