After an expensive upgrade to increase its luminosity, the Tevatron at Fermilab was turned back on in March 2001 to start “Run II”, during which it was hoped that the machine would run with a dramatically higher luminosity than during “Run I” which ended in 1995. During Run I, about 140 inverse picobarns of collisions were generated, at the rate of about 3 inverse picobarns/week by the end of the run. The plan for Run II was for the new machine to get to a luminosity of about 17 inverse picobarns/week soon after the recomissioning, and ultimately to reach about 100 inverse picobarns/week.
This plan turned out to be wildly overoptimistic, as it took nearly a year and a half to get the machine operating even at the luminosity achieved during Run I. During FY02 the initial hope was to accumulate 320 inverse picobarns, rising to 830 in FY03 and 1300 in FY04. Instead 80 were produced in FY02 and 330 in FY03. While in FY02 the machine performed much worse than planned at the beginning of the year, in FY03 it did slightly better than planned.
As this fiscal year (FY04) is coming towards its end, the machine is doing significantly better than planned at the beginning of the year. The last few weeks have seen about 13 inverse picobarns/week being produced. Another measure, the luminosity at the beginning of a “store”, reached a record value on Monday of 8.28×10^31 cm^2/sec. This is about five times higher than achieved at the end of Run I. You can follow the progress (as well as the trials and tribulations) of the Fermilab accelerator physicists through on-line daily reports and continually updated luminosity charts. For a collection of documents showing the history of the Run II problems and the most recent estimates of what will be achieved, see the proceedings of the latest review of the Tevatron luminosity, which took place last February.
About 2000 inverse picobarns of collisions will probably be needed before the Tevatron experiments can push up the current experimental limit on the Higgs mass (114 Gev) that comes from experiments at LEP. There now seems to be a good chance the Tevatron will get to this point before the LHC starts operating at much higher energy in FY 2008. If the LHC achieves anything like its design luminosity, it will quickly make the Tevatron obsolete. Then again, having seen how hard it was to get the upgraded Tevatron running, the job of commissioning the LHC may not be so easy…
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