Tevatron to Carry On

The Physics Advisory Committee at Fermilab have announced their decision to continue running the Tevatron until 2014. It is easy to see why they want to do that: This years published results have strengthened the case for a light Higgs sector. In the mass range up to 150 GeV the rival Large Hadron Collider does not have such a big advantage and wont make the Tevatron obsolete until around 2014 when it’s higher energy and luminosity will finally trump the Tevatron at all mass scales. In the meantime the Tevatron will double its current database of collision events which currently stand at around 9/fb, although Most of the results shown this year only used about 6/fb, so by the time they finish they will be using about three times the data. That should be enough to give a clear signal for where the Higgs mass lies. If there is a more complex Higgs sector with charged multiplets they should have a good indication of that too. According to Fermilab other exciting measurements include the search for supersymmetric Higgs bosons at large tanβ, measurement of the forward-backward asymmetry of the top quark, and the di-muon charge asymmetry in neutral B decay, as well as further improvement in the measurement of the top-quark and W-boson masses.

Any of these things would be an exciting discovery beyond standard model physics and would completely change the Tevatron’s place in history, so it is no surprise they want to go on, but in the grander scheme of things it is not such a good move.  By 2014 the LHC will be surpassing the Tevatron and could well beat them to the most interesting discoveries. At best the Tevatron will share some of the glory unless the LHC has another  significant failure that pushes back their schedule. Meanwhile, other experiments and developments at the Tevatron will not be able to progress so well, both because their budget suffers and because the Tevatron is needed to power them. This includes NOvA, LBNE, Mu2e, and Project X. For longer term progress in high energy physics it would be better if Fermilab concentrated on those efforts.

Meanwhile at CERN the planning council has approved a five-year plan that makes some significant cutbacks in their projects. During 2012 while the LHC is off-line for maintenance, they have now decided that all other experiments on the CERN complex will also be halted. This will push back future plans while allowing the medium term LHC goals to be unaffected. Studies for the next Linear Collider will be slowed and some planned upgrades to the LHC will also be delayed. This is seen as a short-term cutback due to harsh economic times but it could easily turn into a series of pullbacks from cash-strapped governments who are beginning to question the wisdom of expensive research with no direct payback.

It has been suggested that the LHC plans are ambitious with still an order of magnitude of improvements in luminosity to reach the 100/µb/s target by end of october. Even if they achieve this they will need another factor of two next year to be able to collect the 1/fb they want during 2011. But the LHC commissioning process has in fact been going very well with most targets they have set being reached or exceeded so far. Sometimes they face setbacks as they work to push the machine to new heights, but time can be made up as luminosity increases. For the last three weeks the LHC has made no physics runs while preparations are made for the next stage of running. In the next few days they will be colliding again with three major improvements. The separation between proton bunches will be reduced from 1000  µs to just 150 µs and a larger crossing angle of 100 µrad will be used at the collision points to keep the bunches apart before they meet. The speed at which the magnets can be ramped up to increase the beam energy has also been improved by a factor of three to give a significantly better turn round time between runs. With these changes it should be possible to step up the beam luminosity by adding more bunches in a veritable crescendo of activity before they switch to heavy ion physics in November.

The results of the next few years at the Tevatron and LHC will be critical for the future of fundamental physics. If the Tevatron and LHC find supersymmetry it will show that the theorists have been on the right lines for the lats few decades after all and we will see business as usual once again. If only the standard model is found the superstring doubters will come out in greater force and the impact on theoretical physics research around the world could be devastating, even though supersymmetry at the weak scale is not a definitive prediction. Other scenarios are possible if unexpected discoveries are made.

10 Responses to Tevatron to Carry On

  1. Bill K says:

    Thanks for this report Phil! As usual viXra is the best place on the web to find accurate, detailed up-to-date information on the LHC. I have a few comments.
    Regarding the Tevatron, the error bars go as sqrt(N), right? So tripling the dataset improves the statistics by sqrt(3), i.e. by 73 percent. As you say, this will give us an ‘indication’ of the Higgs mass. Question: why does it take them so long to process the data? By now the steps should be virtually automatic. We were all delighted how quickly data analysis from the LHC came out, yet the Tevatron analysis always lags several months behind.
    Regarding the LHC, things do appear to have been going well for the last few weeks, although they still seem to be running behind the most recent schedule, which called for 96-bunch collisions by now and very sizeable increases each week of October. Note they’re now planning for total luminosity only “approaching” 1/fb. Which could likely mean half of that. I think their caution is extremely wise, even if the original target is not literally met.

  2. Philip Gibbs says:

    CDF and DZero say they can also improve their results with better analysis. I think the projections show that they should be able to get a 3 sigma signal for the Higgs wherever it is with that amount of data.

    The LHC has released data quickly where it has been in line with known physics. It is easy to know you got the analysis right if the physics is already known from previous accelerators and you agree with it. They have not shown all possible results with the largest possible datasets at recent conferences. That is probably partly because of the need to concentrate on a selection of the most important results to have them ready on time. It could also be that if any result showed something they did not expect then they would have to spend more time on it to find or eliminate unexpected sources of systematic errors.

    If any signal is real then they are going to spend a lot more time checking and reviewing before they allow the result to go outside the collaboration. The Tevatron is at a stage where its results are starting to show more new results, so it is not surprising that it takes longer for them to approve any analysis. Given the amount of things they have to take into account I find it impressive that results from both accelerators are coming out so fast. I dont believe they can be accussed of sitting on it.

    The LHC is about a week behind their plan but they have been in that situation before. Once they have everything setup to run with the new parameters they will be able to increase the number of bunches quite rapidly. The main thing holding them back will be caution. They dont want any mishaps. There is always a possibility of more delays but they look like they are nearly ready to start physics runs again and there is no reason to think they wont meet this year’s targets.

    Next year they could run for the nine months available using the luminosity they should reach this year, and then they would probably accumulate about 0.5/fb given a reasonable level of efficiency. Alternatively they could reserve two or three weeks to adjust the bunch spacing down to 75ns to add more bunches in and double the luminosity. If they did that early enough they might aim for the orginal target of 1/fb. I expect this will be discussed in depth at Chamonix and the decision will depend on how smoothly the runs have been going, among other things. This is just me guessing from outside, other plan details might emerge at any time.

  3. Kea says:

    There are no fairy fields.

    • Philip Gibbs says:

      You are with Hawking on that one! I can’t say I see it myself, but such a surprise would not go amiss, so long as they also find an explanation for it.

  4. Lawrence B. Crowell says:

    I am not much of an accelerator physics person, but my understanding is the LHC is still at a low luminority which makes Higgs data difficult. The Tevatron folks I know are pushing for a Higgs coup d’tete, I suppose to get the last USA particle physics win. It will be a long time before the US takes the lead again — if ever. The big thing to wait for is a charged Higgs to get some support for MSSM.

    • Philip Gibbs says:

      The LHC will be matching the luminosity of the Tevatron soon enough and the Tevatron can not realistically hope for much more than an indication of the Higgs’s existance. A solid discovery will have to come from the LHC. I agree they might come up with some good support for supersymmetry, it’s a long shot though.

      The US is officially joining CERN. I think if they want to do serious high energy physics experiments on US soil in the future the best bet is to concentrate on the other projects at Fermilab.

      Is that “coup de tête” or “coup d’état”? 🙂

      • Lawrence B. Crowell says:

        Fermilab should probably be converted to an ion collider machine. A tevatron scaled RHIC would produce new physics data. It would particularly be useful with AdS/QCD physics which seems to be hinted at by RHIC. Of course there are some long term “plans” to convert the LHC into an ion collider in 20 years or so, which will race ahead of FNAL.

        Beyond that time frame the main thrust of high energy physics will probably have to be with high energy cosmic rays. In some sense the atmosphere of the Earth is a sort of scintillator and with the right detection devices the physics of 10^2 to 10^5 TEV particles could be studied by this “remote method.”

      • Philip Gibbs says:

        The LHC is already configured to do heavy ion collisions and the ALICE detector is dedicated to that. They will do the first heavy ion collisions this November according to current plans.

      • Lawrence B. Crowell says:

        I guess I was under the impression that the lead ion experiments were not slated to turn on for another decade or two. I have to admit I am not that plugged into the daily news on the LHC.

  5. Lawrence B. Crowell says:

    I meant luminosity above. As for fairy field, well the dirac monopole has a tail and if it is not removed by topology I suppose … . Ok I’ll get my hat and coat and find my way out. 🙂

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