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PEP-II and BaBar Shutdown Begins Today

Early this morning, the BaBar detector stopped taking data and PEP-II crews began powering down the rings for a three-month downtime.

During the seven and a half month run, PEP-II delivered 90 inverse femtobarns of integrated luminosity, a measure of the number of particle collisions in a given period of time. In August, the machine began breaking certain PEP-II records, including the best 30 days ever for integrated luminosity (19.7 inverse femtobarns) and the best week (5.4 inverse femtobarns). Peak luminosity came within a few percent of the record from the previous run, but in the beginning, the machine did not perform as well as hoped for during Run 6.

"It's been a hard fought run, but it's ending very well," said John Seeman, Head of the Accelerator Systems Division. "We appreciate all the groups at SLAC who contributed to PEP-II operations."

The BaBar detector efficiently collected data from the collisions provided by PEP-II. The collaboration has already presented results that include Run 6 data at conferences this summer.

"In its first run with a fully upgraded muon identification system, the BaBar detector performed very well," said BaBar Spokesman Hassan Jawahery. “The collaboration’s excitement about the program remains very strong, and we're grateful to our PEP-II colleagues for their dedicated efforts in operating the machine, and at the same time attempting to raise its luminosity."

During the downtime, PEP-II crews will be busy with a number of upgrades, routine maintenance, and yearly safety checks. Upgrades include installing several new vacuum chambers in the interaction region near the detector and putting in 150 new radio frequency seals between chambers in the High Energy Ring. Both upgrades should allow the accelerator to run with higher currents, and thus better luminosity.

No major upgrades are planned on the detector side. The BaBar collaboration will take care of routine maintenance and investigate and correct a few problems. Run 7 is slated to begin in early December.

Heather Rock Woods, SLAC Today, September 4, 2007

Above image: The PEP rings.