REPORT 1996

s befits a particle detector named for the Titan who bore the world on his shoulders, Atlas will be the most ambitious such project ever undertaken. Proposed for the Large Hadron Collider in Europe, Atlas is designed to capture and detect all the particles created out of collisions between highly energized beams of protons. The primary purpose is to answer one of the age old mysteries of science-why do objects have mass? Atlas will also be used for studies of top quark decays and searches for the phenomenon known as supersymmetry. Though Atlas is destined for Europe, the design and construction will involve more than 400 physicists from around the United States.

The Silicon Vertex Tracker for the BaBar experiment at SLAC. The tracker will measure particle vertices with a precision of less than one-tenth of a millimeter, making it possible, for the first time, to study the phenomenon of CP violation, essential to our understanding of the nature of the Universe.

BaBar is closer to home, destined for the B-factory accelerator now being assembled at the Stanford Linear Accelerator Center. This detector system is being designed to measure the distance between the points of decay for the subatomic particles known as B mesons and anti-B mesons. In the language of particle physics these matter and antimatter particles are signified "B/B-bar"-hence the naming of the detector after the familiar cartoon elephant. The purpose of the BaBar detector is to study matter and antimatter differences, particularly the phenomenon known as CP violation. Understanding CP violation could answer another vexing question of science: Why, during the first split-seconds of the Big Bang, did the process of creation favor matter over antimatter?

Still another big scientific question now being tackled on a national and international scale is "deceleration"-the rate at which the expansion of the universe is slowing down. The answer lies in the stars, namely Type Ia supernovas, the nuclear conflagrations that result from the implosion of a white dwarf. Type Ia supernovas serve cosmologists as a measurement of distance and a means of calculating the velocity at which galaxies are receding from Earth. It is thought that analyzing the spectrums of about 50 type Ia supernovas will be enough to determine the universe's rate of deceleration.

In December of this past year, a collaboration known as the Supernova Cosmology Project (SCP), led by Berkeley Lab scientists, announced the discovery of 11 new Type Ia supernovas, including several of the most distant stars ever observed. These supernovas were discovered within a 48-hour period, an unprecedented achievement that validated a Berkeley Lab technique developed to make deep space supernova discoveries possible and eventually even routine. The discoveries in 1995, combined with discoveries in 1993 and 1994, bring the total of Type Ia supernovas identified by the SCP collaboration to 18.

One of the 11 new Type Ia supernovas discovered in December 1995 by researchers from the Supernova Cosmology Project, led by Berkeley Lab scientists.

Not only is the supernova project an example of a multi-institutional collaboration spanning national borders and oceans, it also an example of institutional cooperation. The Berkeley Lab scientists leading the project are affiliated with both the Laboratory's Institute for Nuclear and Particle Astrophysics, and the Center for Particle Astrophysics on the UC Berkeley campus.

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