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Press Release: B Factory Achieves First Collisions

Date Issued:July 30, 1998


  • Office for Communications, Stanford Linear Accelerator Center: Telephone: 650-926-8703 Fax Number: 650-926-8793

A sophisticated new "particle smasher" at Stanford University built to explore the difference between matter and antimatter came to life this week with the successful achievement of its first collisions.

Physicists circulated beams of electrons and and their antimatter opposites, known as positrons, simultaneously in two evacuated rings, each more than a mile around. When they brought the narrow beams together at a single crossing point, they observed the deflection and disruption of one beam by the other -- a sure sign that head-on collisions had occurred.

Funded by $177 million from the U.S. Department of Energy, the Asymmetric BFactory is a joint construction project of the Stanford Linear Accelerator Center (SLAC), Lawrence Berkeley National Laboratory (LBNL), and Lawrence Livermore National Laboratory (LLNL). This dual-ring machine is an extensive upgrade of an existing electron-positron collider at SLAC. Construction began in 1994 and was completed in early July, on budget and on schedule.

The collider is now in the midst of a long tuning process, or commissioning, that will continue into the spring of 1999, when the machine will begin operations for physics research. In January a 1000 ton particle detector known as BaBar will be moved into position at the point where the two beams intersect.

Built by a large international collaboration of more than 500 physicists and engineers, this detector is designed to search through the debris of electron-positron collisions for evidence of short-lived subatomic particles known as B mesons. By comparing the production and disintegration of these particles with those of their antiparticles, physicists hope to learn more about the differences between matter and antimatter that led to the Universe being composed almost entirely of matter.

Under Secretary of Energy Ernest Moniz congratulated the three laboratories involved and especially the B Factory team, saying, "This is a truly impressive accomplishment so early in the commissioning process. The B Factory will help us examine one of Nature's great secrets -- why the Universe has such a preponderance of matter over antimatter."

The Asymmetric B Factory is the world's first particle collider in which the electrons and positrons meet at unequal energies: electrons have almost three times the energy of positrons. Because of this difference, plus the need to circulate high currents in order to produce millions of B mesons, physicists have designed a machine with the two different kinds of particles traveling in two separate rings.

A complex array of magnets before and after the crossover point brings the beams together and then separates them after they clash. These magnets also focus the beams down to small dimensions in order to enhance the chances of obtaining electron-positron collisions.

"I am very pleased that we have achieved collisions so soon after finishing construction," said SLAC physicist Jonathan Dorfan, the project leader. "We look forward with great anticipation to completing the commissioning process and beginning the physics program next year."

Commissioning of the B Factory has gone smoothly, with few surprises - a testament to the expertise of the accelerator physicists who designed and built this state-of-the-art machine. It resumes in October with attempts to boost the collision rate.

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Artist's conception of the Asymmetric B Factory. The existing linear accelerator at SLAC delivers energetic electrons and positrons to two separate storage rings in the PEP-II facility. These particles circulate in opposite directions and collide with one another at a single crossing point, soon to be surrounded by the BaBar detector.
(SLAC drawing by Terry Anderson)


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View down the tunnel of the Asymmetric B Factory. Electrons circulate clockwise in an evacuated copper tube inside the lower ring of magnets, here being examined by SLAC physicist John Seeman and Caltech physicist David Hitlin. The positron beam travels the other direction in the upper ring, through the yellow and blue magnets just behind them, at about one third the energy of the electrons.

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