APS News

Highlights form Columbus, OH Spring Meeting: "Cosmic Chords," Quark Gluon Plasmas

Approximately 1,200 physicists assembled in Columbus, Ohio, for the 1998 Joint Spring Meeting of the APS and the American Association of Physics Teachers (AAPT), 18-21 April. The Spring Meeting explored current topics in particle physics, astrophysics, fluids, particle beams, physics of beams, nuclear physics, applications, plasmas, and atomic, molecular and optical physics. Topics of technical sessions included the discovery of "cosmic chords", changing hadron masses in the nuclear environment (see page 3), and evidence of the first observation of the quark gluon plasma. Nontechnical sessions included such topics as communicating physics more effectively, educating physicists for nontraditional careers, and current issues in science policy, arms control, and technology transfer.

In addition, the AAPT organized several sessions devoted to issues in education, some in conjunction with APS committees or units. The traditional ceremonial banquet for the bestowal of prizes and awards was held Saturday evening, preceded by a reception hosted by APS President Andrew Sessler (Lawrence Berkeley National Laboratory). Fourteen prizes and awards were presented, and the recipients gave lectures on their respective topics at various sessions throughout the week. Citations and brief biographies of the recipients appeared in the April 1998 issue of APS News.

Technical Sessions

Cosmology Today

Astrophysicists reported the latest news about events occurring at the edge of the universe at a Friday workshop. Recent observations of distant supernovas suggested that the expansion is not slowing down at all but rather speeding up, according to Robert Kirshner of Harvard, one of the leaders of this supernova effort. Wendy Freedman of the Carnegie Observatories summarized her work to measure the Hubble Constant in the relatively nearby space, using the Hubble Space Telescope. David N. Spergel of Princeton University, who is mapping tiny fluctuations in the cosmic microwave background with the Microwave Anisotropy Probe (MAP) to be launched in the year 2000, discussed how to sharpen our estimates of various cosmological parameters (such as the expansion rate and the baryon density). Edwin Turner, also of Princeton, described how he uses gravitational lensing to calculate the age of the universe.

In other astrophysics news, the most distant gamma ray burst, at a red shift of 3.4, was discovered in December and observed at several wavelengths. Optical measurements (yielding a red shift) of the object were announced by Caltech astronomer Shrinivas Kulkarni. Optical astronomers were led to the burst's spot in the sky by x-ray observations made by the BeppoSax satellite.

The Size and Shape of the Deuteron
Abdellah Ahmidouch, North Carolina A&T State University, and Betsy Beise of the University of Maryland described results from the t20 experiment at the Jefferson Laboratory in Virginia. This experiment has gained new information on the shape and size of the deuteron. This new experiment is the first to resolve details of the deuteron structure down to a fifth of the proton's size. Surprisingly, and contrary to some theoretical predictions, the experiment showed that even at this small scale the deuteron can still be described perfectly well by "classical" nuclear physics as a system of a proton and a neutron loosely held together, without considering the fundamental building blocks of the particles, namely quarks and gluons.

Electromagnetic Probes of Nuclei
Many present-day nuclear physics accelerators shoot an electromagnetic probe, such as an electron, at nuclei to uncover detailed information about their properties. A Saturday morning session featured recent results from numerous electromagnetic facilities and detectors around the world. For example, Edward R. Kinney of the University of Colorado and DESY presented new results from the HERMES experiment at DESY in Germany which provide detailed experimental information on nuclear spin, a quantum property which describes how a nucleus interacts with magnetic fields. Finally, Pete Markowitz of Florida International University discussed the results of Jefferson Lab experiments that probe the formation of omega mesons, short-lived and highly unstable nuclei consisting of two quarks.

Measuring Planck's Constant
In efforts to come up with the most precise value of Planck's constant to date, a NIST group led by Edwin Williams has performed experiments that relate Planck's constant to mechanical measurements of a kilogram mass attached to a coil in a magnetic field. With these measurements, they were able to determine Planck's constant to an accuracy of 0.15 parts per million. The group is working to increase the accuracy of their measurement tenfold, and their experiments overall aim to lead to a definition of the kilogram based on quantum units, rather than one based on the stalwart physical artifact currently stored in France.

Looking for Cracks in the Standard Model
The current theory of particle physics, the standard model, has been successful in accounting for most of the violent phenomena observed at accelerators. Still, researchers must always be on the lookout for anomalies that point to new physics. Bruce Strau (Columbia University) from the HERA collaboration in Hamburg, Germany, reported electron-proton collisions evidence for bizarre particles called leptoquarks. Sarah Eno (University of Maryland) reported on recent experiments at Fermilab, where the Tevatron's 1.8 TeV of collision energy can hypothetically reincarnate quarks into various exotica, such as Higgs bosons and supersymmetric particles. Ian Scott (University of Wisconsin) summarized new results from the LEP electron-positron collider.

Light-Front Field Theory
Physicists believe that a proton is made up of three quarks held together by particles known as gluons. Each proton is constantly bathed in a sea of virtual particles, making it difficult for the modern theory of particle physics, known as quantum chromodynamics (QCD), to describe the properties of a proton's constituents in isolation from its surroundings. In the early 1970s, Richard Feynman suggested that it would be easier to separate the proton from virtual particles if the proton was moving near the speed of light, relative to a fixed point-of-view. In such a reference frame, one would know that the proton's constituent particles were also moving at near-light speeds, while it would be much less likely for the virtual particles to be traveling at such velocities.

This "light-front" approach has explained some key results in particle physics experiments, but it has not been possible yet to compute the properties of high-energy (excited) states of the proton from first principles in this (or any other) framework. The primary barrier to computation has been the belief that quarks in a proton are strongly bound to gluons, which makes computation difficult. In a new version of the light-field approach, Nobel Laureate Kenneth Wilson and Robert Perry of Ohio State University, Stan Glazek (Warsaw University), and others propose that quark binding is considerably weaker than expected; the only strong binding is of gluons to each other, and that this is enough to prevent the appearance of free quarks. Such an assumption may lead to greater success in analyzing the excited states of the proton and of other objects containing quarks.

Rare Processes in Spontaneous Fission
An international collaboration of researchers from thirteen institutions in the U.S., Romania, Germany, Russia, China, and Brazil has discovered that along with normal fission, neutronless fission in some elements like Californium is also possible. According to Vanderbilt University's A.V. Ramayya, there are several processes, such as californium splitting into molybdenum and barium, which is called cold (neutronless) binary fission. Usually 1-10 events of this type occur per 10,000 total fission events of 252Cf. This rare process could not be detected until recently because of the lack of sensitivity in detector systems. At a cost of $20 million provided by the U.S. Department of Energy, a 110-gamma-detector array called Gammasphere was constructed in the U.S. These data provide significant new insight into the fission processes and particularly the theoretically predicted cold fragmentations of nuclei.

Sensing with Luminescent Materials
Fluorescence characteristics of the rare earth elements are particularly favorable for use in optical thermometry. The first commercial fiberoptic temperature sensor become available in the early 1980s, with significant improvements in product design and performance since then. In addition, the development of rare earth doped fibers for communications purposes has opened up the possibilities of new all-fiber systems capable of making measurements with compact probes. At a Tuesday morning, John Sullivan of Purdue University discussed the use of luminescent molecular probes to obtain surface pressure distribution measurements on wind tunnel models, flight vehicles and other fluid flow rigs. His technique imbeds luminescent molecular probes in a binder to form a pressure sensitive paint (PSP). On excitation by light of the proper wavelength, the luminescence, is detected by a camera or photodetector.

Accelerator-Driven Transmutation of Waste
Nuclear waste from commercial power plants contains large quantities of plutonium, other fissionable actinides, and long-lived fission products that are potential proliferation concerns and create challenges for long-term storage. The current U.S. policy is to store unprocessed spent reactor fuel in a geologic repository. However, long-term uncertainties are hampering the acceptability of this approach.

Accelerator-driven Transmutation of Waste (ATW) concept offers the U.S. and other countries the possibility to greatly reduce plutoinium, higher actinides and environmentally hazardous fission products destined for permanent storage. Spent fuel would be shipped to the ATW site where the hazardous waste products would be destroyed by fission or transmutation in their first and only pass through the facility, using an accelerator-driven subcritical burner cooled by liquid lead/bismuth and limited pyrochemical treatment of the spent fuel and residual waste. "ATW does not eliminate the need for, but instead enhances the viability of permanent waste repositories," said Venneri, adding that ATW also brings to the table new technologies that could be relevant for next-generation power producing reactors.

Physics Laureates
Nobel Prize winners seldom rest on their laurels. All three of last year's recipients of the Nobel Prize in Physics described their current research in Monday sessions. Steven Chu of Stanford University reported on the physics of DNA molecules which, because of their mechanical, self- assembling and molecular-recognitions properties, are potentially useful building materials for nanotechnology. William Phillips of NIST described tenuous crystals in which the atoms are held in place not by chemical forces, but by laser beams, forming so-called "optical lattices," a periodic pattern of potential wells that confine the atoms in a regular lattice. Claude Cohen-Tannoudji of the College de France et Laboratoire Rastler Brassel described prize winning research on manipulating stars with light.

Nontechnical Sessions

Voodoo Science
Robert Park of the University of Maryland, author of APS's weekly report "What's New," received the Joseph Burton Award of the Forum on Physics and Society for his colorful commentary on public issues relating to science at a Saturday morning. He is notable for his crusade against pseudo-science or, as he likes to call it (in those cases where the notoriety of the results far exceeds the experimental support), "voodoo science." Also honored at the same session were the 1998 recipients of the Leo Szilard Award: David B. Goldstein of the National Resources Defense Council and Howard Geller of the American Council for an Energy-Efficient Economy, who spoke in favor of enacting new national efficiency standards for equipment for meeting future climate goals at a profit.

Science Wars
In 1996 NYU physicist Alan Sokal sent a hoax article to the journal Social Text, a journal devoted to "Science Studies," the sociological study of science. The article subtly lampooned many of the arguments used by other authors in the journal. The ensuing acrimony over the hoax, and the numerous letters to the editors of various publications has added a new sharpness to the debate over the objectivity and cultural role of science. At a Saturday morning session, three observers of this ongoing "science war" offered their perspectives on the controversy: George Levine, an English professor at Rutgers University; Ullica Segerstrale, sociologist with the Illinois Institute of Technology; and physicist Kurt Gottfried of Cornell University.

Current Policy Issues
In November, the White House issued a report from the President's Committee of Advisors on Science and Technology (PCAST), entitled Federal Energy Research and Development for the Challenges of the Twenty-First Century. The report addresses why U.S. funding for this program is important, and recommends many changes in the current federal portfolio. During a Monday morning session, John Ahearne (Duke University and Sigma Xi), a member of the PCAST panel that issued the report, summarized the recommendations within the context of the recent Kyoto meeting on climate change. At the same session, Jo L. Husbands of the NAS' Committee on International Security and Arms Control outlined the basic conclusions and recommendations of the Committee's report entitled, The Future of U.S. Nuclear Weapons Policy. That recommends deeper reductions in nuclear arms and fundamental changes in the policies that govern nuclear operations.

Communicating Physics Effectively
Several scientists with considerable expertise in writing or lecturing about physics were featured at a Monday morning session on how to communicate physics more effectively. Barbara Levi, a long-time editor of Physics Today, shared some of the lessons she has learned over the years about how best to translate research results from various physics subfields. Hans Christian von Baeyer of the College of William and Mary, who has written widely about physics for general audiences, expressed his belief that no less than 5% of the total effort of every physics department should be devoted to the popularization of physics, to combat the threats of anti-science, pseudo-science and general indifference to science. "Popularization of physics is changing from a genteel art to a necessity for survival," said von Baeyer, offering several hints and suggestions for effective science writing.

Special thanks to Philip F. Schewe and Benjamin Stein of the American Institute of Physics' Public Information Office for contributing to the coverage of technical sessions in this issue.

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Editor: Barrett H. Ripin