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In this issue:
Still Running at SSRL
Science Today: The Mystery of the Higgs Particle(s) and Unification
Physics Nobel Laureate Melvin Schwartz Dies

SLAC Today

Thursday - August 31, 2006

The microsource x-ray generator, along with the SSRL Automated sample Mounting (SAM) robot. (Click on image to see larger version.)

Still Running at SSRL

The annual shutdown of SPEAR3 brings anything but idleness to SSRL. Having the storage ring switched off gives engineers and scientists time to make upgrades and repairs, keeping the beehive of activity at the lab humming. And just because no x-rays shine down SPEAR3's beamlines, that doesn't mean scientific research comes to a halt.

Of the recent technical achievements at SSRL, perhaps the one that has most enhanced the scientific productivity of the macromolecular crystallography user community is the robotic sample-handling system, in use on all six crystallography beamlines (see SLAC Today story here). But each year, even as those robots remain ready for action around the clock, the annual shutdown leaves researchers with three months of darkened beamlines and, subsequently, idle robots. In 2003, as a means to bridge that gap in the calendar, scientists finally found a way for the robot at Beamline 9-2 to earn its keep during the down time.  Read more...

Spare the Air

Tomorrow, Friday, September 1, is a Spare the Air Day in the San Francisco Bay Area. Ground-level ozone air pollution is forecast to exceed 100 AQI (Unhealthy for Sensitive Groups) tomorrow due to clear skies, hot temperatures, a strong temperature inversion trapping pollutants near the ground, and light winds.
More information...

(Daily Column - Science Today)

The Mystery of the Higgs Particle(s) and Unification

One promising candidate for a theory of physics beyond the Standard Model is Supersymmetric Grand Unification. This is a beautiful world in which all of the distinctions among particles—quarks versus leptons, fermions versus bosons, force versus matter—are erased. But it is hard to see this world, for if we have simplified the theory so much, how can we explain the variety of elementary particles and their interactions that we see in nature? One explanation is that even though the particles in the theory are all interconnected by symmetry, the "vacuum"—the underlying space itself—is very asymmetrical. As the particles move through space, they feel this asymmetry and behave differently.

Theorists attribute this asymmetry of space to the presence of something called Higgs fields, which exist throughout space and take on these asymmetrical configurations. In the Standard Model, there is one Higgs field that distinguishes electrons from neutrinos, up from down quarks, and W bosons from photons. In a grand unified theory, there must be another Higgs field that distinguishes quarks from leptons and W bosons from gluons. In a supersymmetric theory, there must be yet another Higgs field that distinguishes the familiar particles from their s- or -ino partners. The more beautiful the theory, the more unexplained Higgs fields. Where do they all come from?

It is not so easy even to build a model with so many Higgs fields, because multiple Higgs fields lead to paradoxes. For example, grand unification relates the necessary Higgs field of the Standard Model to a completely unwanted Higgs field that can lead to too rapid proton decay. The Higgs field that distinguishes supersymmetry partners can destroy the good features of the Standard Model unless it couples to the Standard Model Higgs field in a very particular way. In simple models of Grand Unification, neither problem is solved, and models that fix the problems are usually very complicated.

Recently, I realized that there is an interesting possible solution to this network of problems: Adding to the usual elements of Supersymmetric Grand Unification a new strong force operating at very short distances. This strong force begins the deformation of the vacuum and sets up its asymmetric structure. The three different kinds of Higgs fields are formed as bound states of the elementary particles under this new strong force. Their interactions turn out to be just as required to solve the problems presented in the previous paragraph. In fact, I built an amazingly simple model along these lines, in which the three kinds of Higgs field are unified as different combinations of the same constituents.

Although the new force acts at distances much too small to be seen directly, the model is testable. In the next few years, mass measurements of supersymmetric particles made at the Large Hadron Collider (LHC) and the International Linear Collider (ILC) will offer exciting tests of this and other models of particle unification.

Physics Nobel Laureate Melvin Schwartz Dies

(Image - Melvin Schwartz)Melvin Schwartz, a Nobel prize winner who worked at SLAC for nearly two decades, died Aug. 28 at a Twin Falls, Idaho, nursing home after struggling with Parkinson's disease and hepatitis C. He was 73.

In 1988, Schwartz shared the Nobel Prize with Leon Lederman and Jack Steinberger "for the neutrino beam method and the demonstration of the doublet structure of the leptons through the discovery of the muon neutrino."

"Mel Schwartz proposed and subsequently carried out [with Jack Steinberger, Leon Lederman and four younger colleagues] the first accelerator neutrino experiment, which demonstrated the existence of neutrino flavors," Professor Stanley Wojcicki, chair of Stanford's Physics Department, wrote in an e-mail interview. "This experiment was the forerunner of a rich experimental program all over the world utilizing accelerator neutrino beams, which discovered neutral currents and contributed significantly to the establishment of the Standard Model of particle physics. Mel deserves to be known as the father of accelerator neutrino physics."

Sidney Drell, a professor emeritus at SLAC, recounted how physicists discovered the fundamental patterns of subatomic particles that advanced the field. "We had studied the electron and we learned that for the weak forces, which are important in radioactivity, they were associated with a neutrino," he said. "When we discovered the muon in the 1940s, in every way it was just like an electron—only about 200 times heavier!" Scientists set out to understand what the muon did in weak interactions. The muon was also associated with a neutrino. But was it the same neutrino with which the electron was associated, or was it a different one?

"The neutrino was an extremely elusive particle, but [Schwartz] found a way to make a beam of them at Brookhaven [National Laboratory]," Drell said. "He, Lederman and Steinberger, the three managed to show that the muon's neutrino, though very similar in many ways to the electron's neutrino, was a different particle. Subsequently, these two families of so-called 'lepton doublets'—the electron and its neutrino, and the muon and its own neutrino—acquired a third cousin when SLAC physicist Martin Perl went on to discover the tau lepton at SLAC, for which he received the 1995 Nobel Prize in physics."

Born Nov. 2, 1932, in New York City, Schwartz attended the Bronx High School of Science and went on to earn bachelor's and doctoral degrees in physics from Columbia University in 1953 and 1958, respectively. After working in Brookhaven National Laboratory as a research scientist from 1956 to 1958, he joined the Columbia faculty as an assistant professor in 1958 and went on to become an associate professor in 1960 and a professor in 1963.

In 1966, Schwartz joined the Stanford faculty and began conducting research at SLAC. "We saw the first beam in the summer of 1966," said Wojcicki. "Mel and the beam arrived at the same time." Read more...

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