Tough Week for the LHC

Today the Large Hadron Collider has taken another step up  in luminosity by increasing the number of proton bunches per beam from 1092 to 1236. The first run at this new intensity equaled the previous luminosity record. They may beat it in subsequent runs by pushing up the bunch intensity. One more step up is required to reach this years maximum possible bunch count of 1380 bunches per beam. It may be too late to reach that step before the next technical stop.

The advance comes at the end of a tough week with only one run during a period of five days. At least that one run was itself a record with integrated luminosity for a single run of 47.7/pb in ATLAS. For CMS the total delivered was 46.3/pb but they issued a special note to say that they had also recorded 44.3/pb, more than the entire amount recorded during 2010.

The main reason for the delay this week was problems with cryogenics caused by clogged oil filters and possibly worsened by a lightning strike and/or an industrial strike. When any one of the 8 major cryongenic plants fails it can easily take two days to get it fixed and return the superconducting magnets to their working temperature of 1.9 degrees Kelvin. There were two such outages this week with this record run in between.

Update 27-Jun-2011: The situation has improved in the last few days culminating in a run today lasting about 20 hours that delivered a record 62/pb. The luminosity was still above half its peak value at the end of the run demonstrating just how good the luminosity lifetimes are. The next run will attempt 1380 bunches, the maximum possible with 50ns spacing. They have just one day left before machine development time takes over, followed by a technical stop.

13 Responses to Tough Week for the LHC

  1. Tony Smith says:

    “Tough Week” indeed from what you say, Phil.

    Lightning strikes are just part of weather and can be dealt with in due course,
    two things you say really worry me:

    1 – Who is responsible for keeping the oil filters etc clean?
    As I saw in the Air Force, the maintenance/mechanics are the people who keep airplanes flying (colliders running) and have as much (maybe more) internal prestige within the organization (collaboration) as the pilots (control room guys)
    both of which
    have much more real internal prestige than base command administration guys (committee bureaucrats).
    How is it at the LHC ?
    Do the people that do the dirty work to keep things running get the respect they deserve ?

    2 – Your “industrial strike” link raises questions (related not only to 1 above but also to overall financing) when it says “The voice of the staff has been practically ignored” with respect to a pension funding “Diktat by the Member States”.
    This sounds sadly like the leading edge of funding withdrawal by the member states, probably related to the obvious problems of the Euro and its member states.
    If Greece is only the first domino to fall, then the question is whether Germany and France (maybe the only financially sound members – the UK has problems similar to the USA) will take on the LHC themselves or let it go (unless maybe China bails it out).

    It seems now with over 1/fb already collected that the LHC within a few weeks will either

    1 – exclude at 95 per cent CL any Standard Model Higgs up to well over 200 GeV/c2
    2 – find 2 or 3 sigma evidence for any Standard Model Higgs below 600 GeV/c2

    If (as I think is likely) case 2 prevails and evidence is found for Standard Model Higgs below 600 GeV/c2
    I worry that the bureaucrats might ignore the distinction between evidence and discovery (4 or 5 sigma)
    and declare Mission Accomplished – God Particle Found
    then say that the LHC should follow the Tevatron into glorious retirement.

    Such things might be discussed at the mini-Chamonix on 15 July 2011
    I do hope that the prevailing view there will be favorable to extending the LHC run beyond the fall of 2011 and on into 2012, at least
    that the people who do the necessary dirty work to keep things going will be treated with the respect they deserve (including tangible things like pay and pensions).


    • Philip Gibbs says:

      Interesting comments Tony.

      On the Higgs exclusion, my understanding is that 1/fb is not sufficient for the exclusion at low mass. That will require 5/fb. However, If could be excluded above 135 GeV on the assumption that the SM holds, but a Higgs mass below 135 GeV requires extra BSM physics for stability, so if they produce that exclusion without positive evidence of any other new particles they are already in a surprising position. There will be much head scratching and wondering why god decided to be malicious after all.

      As to the oil filters, it is a new machine and mistakes will be made, they will learn from them. I dont know if this particular issue was a result of negligence or some contamination in the oil that caused a problem they could not have been anticipated.

      With regard to funding, there will be some very tough choices to be made for countries like the UK. The research budgets are on the slide and they will have to make choices between projects such as LHC, telescopes and local research projects. The LHC is a high profile project with most of the investment already put in. The funds are committed and hard to cut legally. Many scientists are now dependent on it to complete their work. It will generate a lot of public interest very soon. I hesitate to underestimate the willful negligence of the present UK government but I dont think we will see any fatal cuts. Some restrictions may make it hard for them to find the money to fix all of the niggling problems. This may mean it is in stable beams only 40% of the time instead of 70%

      Pension provision has been overoptimistic across Europe and people will have to accept some adjustments unless they expect their children to be burdened with crippling taxes to pay for them.

      The LHC must go on to collect many hundreds if not thousands of inverse femtobarns before it has really explored all the channels it is capable of, and I am sure it will be allowed to do so.

  2. Phil says:

    Only a fool predicts what politicians might decide… but still, I think the LHC is safe. But if the LHC finds a SM Higgs, and nothing else, then the case for a new experiment will be a hard sell.

  3. Bill K says:

    It was the best of times, it was the worst of times…

    “I dont know if this particular issue was a result of negligence or some contamination in the oil” – From the description it sounded like the root cause was a malfunctioning pump. They were lucky the collateral damage was confined to an oil filter.

    “There will be much head scratching and wondering why god decided to be malicious after all.” – Maybe God wants us to build a bigger machine. (At least we should claim that!)

    “With regard to funding, there will be some very tough choices to be made” – Pay ’em by the 1/pb!

  4. carla says:

    Does anyone know why they’re no longer updating the latest news anymore?

  5. Luboš Motl says:

    Well, I was probably the only one who made the bet – in your revised poll – that there would be less than 3/fb of the data in 2011. It’s still plausible it will be the case.

    This not-so-optimistic estimate of mine of course included the appreciation for the fact that people may take breaks, be lazy for a while, and finding excuses in the weather, just like you did, not to speak about some more legitimate problems that sometimes occur.

    • Philip Gibbs says:

      Your 3/fb still looks pessimistic but my 10/fb looks even more optimistic. It has taken longer than expect to reach maximum luminosity, still not there, and time in stable beams has been less than it might have been. 4fb-6/fb looks more realistic now.

    • carla says:

      Perhaps Phil could do another poll on whether people’s estimates have changed, now they can see how problems can routinely occur?

      It’s been a real eye-opener over the last few weeks as to how easily problems can crop up from a change in setup, with very little seemingly being done. Even so, the last 1236b 14 hour fill ran smoothly, benefiting from overcoming the emittance problems they had with 1092b and now there is just one bunch scheme left. They have also solved the rf problem which was preventing them from increasing intensity.

      Two months from now, could the intensity be at 1.5 times what it is now?

      I’d change my estimate from 5-7/fb to 3-5/fb assuming there is a gradual increase in intensity so that 1-1.5/fb is collected for the next 6 week run and 1.5 – 2.5/fb for the final 8 week run.

    • Philip Gibbs says:

      We could always see that problems occur routinely, but the hope was that they would be less when they settled down to a constant process of collecting luminosity rather than increasing it.

      A further factor of 1.5 is only possible if they also push up the bunch intensity by about 16% . That is not yet ruled out as far as I know.

  6. carla says:

    Great news they’re going for a record 1380b on the back of a record breaking 60/ub fill. I hope they push things on this last day so they can see what further problems need to be addressed during the MD and TS over the next 1.5 weeks

  7. They update on a twitter feed now not on the LHC news page.Google lhc news twitter.

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