Tevatron steams on!

I’m always reporting the progress of the Large Hadron Collider so it is good to have a look at the Tevatron for a change. There is an excellent facebook page for the Fermilab collider where they report on the data collected during each store. Over the last week they had a particularly good run and posted this plot.

They collected 78/pb in one week with typical fills of 15 to 20 hours providing as much as 11/pb each time. Given the peak luminosity of 430/ub/s (which by the way was a new peak luminosity record for the Tevatron), the Hübner Factor is about H = 78000/430*3.6*24*7 = 0.3. This is an optimal value for the factor given excellent running conditions with minimal stoppages.  The longer term value is presumably a bit less than this.

The turnround times on a good day last week appear to be about 5 hours between fills. In fact they can refill in as little as one hour when all goes well. This is very good compared with the Large Hadron Collider whose best turnround times have been about 2.5 hours.

Given that a Hübner Factor of 0.3 is exceptionally good at the Tevatron you may wonder how the Large Hadron Collider with its longer turnround times could do better. The answer is that it has much better luminosity halflife times. At the Tevatron half the luminosity is lost every 6 to 7 hours (this is my estimate from above plot). The LHC has been producing halflives of about three times as long. During a run of 19 hours at the Tevatron the Luminosity could drop to as little as 15% of its peak while the LHC would still be at 50%. This is enough to double the Hübner Factor for the LHC.

What are the reasons for the longer lifetime at the LHC? Good question! I can only speculate that it is a combination of factors including the fact that the LHC uses two beam pipes compared with the single beam pipe design of the Tevatron. Keeping the bunches further apart outside the collision points should help stability. The LHC may also have better damping systems to keep the beam focused. It’s larger size gives more scope for correcting the blow-up of emittance. The higher energy also helps I think. Perhaps there are other reasons. The LHC is just a much more up-to-date machine.

For now though, it is the Tevatron that is steadily collecting data to add to its already impressive store. It’s a glorious run to the end of its long and fruitful life in September.


11 Responses to Tevatron steams on!

  1. carla says:

    Using an average turn around of 5 and luminosity half life of 6 hours, I get the optimum running time to be 8 hours, yet they’re running at 15-20. I wonder why?

  2. felix says:

    Hello Philip, a dumb question here. Your earlier post says that the LHC will run for 124 days this year. I’m wondering how many days will the LHC be running in 2012?

    I’m asking this question because I want to have some clue about whether there will be celebrations over a tentative Higgs discovery next year.

    • Philip Gibbs says:

      The schedule for 2012 will be similar to 2011 with a heavy ion run in November, so the number of days for proton physics will be about the same. However, the running parameters may be stepped up.

      It is possible that they will run at higher energy in 2012, e.g. 4 TeV or 4.5 TeV instead of 3.5 TeV. This depends on the result of tests that will be carried out during the end of year shutdown. Even if they stick at the same energy there is potential for increasing luminosity further. They may try a smaller beta and they may go beyond nominal bunch intensities to ultimate bunch intensities. That would double the luminosity. Or they may try 25ns bunch spacing as another way to double luminosity (they cant do both of these at once otherwise the cryogenics would fail)

      This year they will collect at least 5/fb which could be enough for 3 sigma level observations of Higgs. They may get to 10/fb which really should be enough for a proper discovery, or very nearly. In 2012 they could collect another 10/fb – 20/fb. Even if they are still at 3.5 TeV that will be enough to cover the Higgs sector in some detail.

      Even before they discover the Higgs there is potential for other discoveries. Those could appear at any time. It depends on what nature has lined up for us. They will be running analysis with 300/pb now and will report on at least that much in early June (if it does not leak out sooner)

  3. Luboš Motl says:

    It may be praised that the Tevatron is running – but holy cow, the LHC is so clearly vastly superior in pretty much all the quantities, including the immediate luminosity, even when we ignore that it is a luminosity with 3.5 times higher energy.

    • Philip Gibbs says:

      Yes, running the Tevatron beyond September would have been a complete folly. By that time the each of the LHC will be well beyond the Tevatron on all counts. I used the steam analogy because the Tevatron now looks like a steam train compared to the LHC :)

  4. felix says:

    Just to clarify. I was asking whether the LHC will run long enough to find something worthy of celebration next year, not whether the LHC staff will have enough days off (when the machine is not running) to hold such celebrations.

    • Luboš Motl says:

      Dear Felix, the run was extended up to late 2012 exactly because it’s pretty much guaranteed that the LHC will find e.g. the Standard Model Higgs boson by 2012. For the least accessible masses near 115 GeV, you need something like 15/fb for a 5-sigma discovery and it will be achieved by 2012.

      What else the LHC finds strongly depends on what is out there.

      • carla says:

        What chance would you give for signs of susy being found in 0.5/fb, 1/fb, 5/fb of data?

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