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Physics in Philadelphia: From quarks to quasars

Note: Each story is embargoed until the date and time of presentation

College Park, MD, February 28, 2003-----The April Meeting of American Physical Society (APS) will take place April 5-8 at the Loews Philadelphia Hotel in Philadelphia. About 1700 presentations are expected. As usual the subjects to be covered will cover the range of physical reality from the smallest scale---quarks, nuclei, atoms---all the way up to the largest scale---that of galaxies and the universe as a whole. In between come many other topics of interest to physicists: missile defense, Nobel prize lectures, high school students at work on particle physics experiments and geophysics experiments, and Benjamin Franklin as scientist. And whatever parts of the material universe are left out of the April APS meeting---things such as photonic devices, superconductors, interfering RNA, fluid dynamics---will be dealt with at the APS March meeting (March 3-7 in Austin, Texas; *Reporters see note below)

SOME EXPECTED HIGHLIGHTS OF THE MEETING

NEW PROTON SHAPE, NEW NEUTRON IDENTITY
Triggered by state-of-the-art nuclear physics experiments at Virginia's Jefferson Lab (JLab), the University of Mainz, and the MIT-Bates Linear Accelerator facility, physicists are revising basic assumptions about the proton and neutron, the "nucleons" that make up the core of an atom. With high-energy, polarized electrons or photons impinging upon targets containing nucleons, the experiments are yielding surprising results. According to some nuclear theorists, the data provide evidence that the proton is not always spherically shaped, but can regularly assume different shapes. Gerald A. Miller of the University of Washington (miller@miller.phys.washington.edu) asserts that near-light-speed (relativistic) motions of a proton's quarks generate significant orbital angular momentum which can generate a non-spherical shape. At his talk, Miller will display pictures, based on experiment and theory, that show that the shape of the proton can vary from a pancake to a peanut to a sphere. In addition, Miller has developed a new relativistic model of the neutron. Agreeing with recent Jlab data, the model shows that part of the time, a neutron is actually a proton surrounded by a negatively charged pion (a kind of quark-antiquark pair). (Paper B3.003) Other speakers at session B3 will discuss the new experiments and theories on the proton and neutron.

SEARCH FOR GRAVITATIONAL WAVES
The Laser Interferometer Gravitational-Wave Observatory (LIGO) is a facility dedicated to the detection of cosmic gravitational waves. Under construction for the past decade, LIGO has just completed its first scientific runs, and the first official results will be presented at the APS April meeting. (Sessions C5, H5, K9)

PLENARY TALKS
Three sessions will showcase notable speakers holding forth on notable topics. Session A1 features talks on the search for extra spatial dimensions (Joe Lykken, Fermilab), the interplay of new theories and new observational techniques in astrophysics (Martin Harwit, Cornell), and the prospects for building a National Underground Science and Engineering Laboratory (Thomas Bowles, Los Alamos). Session G1 features talks about recent results from the premier x-ray observatory, Chandra (Patrick Slane, Harvard), a review of neutrino experiments (Stuart Freedman, UC Berkeley), and experiments using the decays of B mesons to study the difference between matter and antimatter (David Kirkby, UC Irvine). The third plenary session (N1) concerns the study of the highest energy elementary particle collisions anywhere (Paul Grannis, Stony Brook, former head of the D0 detector group at Fermilab) and the mysterious gamma ray bursts spread across the sky (Ralph Wijers,University of Amsterdam).

OTHER NOTABLE TALKS
Session B6 features 2002 Nobelist Masatoshi Koshiba (International Center for Elementary Particle Physics in Tokyo) and quantum pioneer John Wheeler (Princeton). Speakers at session R15, held at the University of Pennsylvania, include theorist Edward Witten (Institute for Advanced Study), who will discuss the future of particle physics, while Michael Turner (Univ of Chicago) will summarize recent exciting discoveries on the composition of the universe.

WHY IS THE NEUTRON HEAVIER THAN THE PROTON?
Scientists at the Indiana University Cyclotron Facility have made the first unambiguous identification of a rare process, the fusion of two nuclei of heavy hydrogen to form a nucleus of helium and an uncharged pion, one of the subatomic particles responsible for the strong force that binds nuclei together. This process would not exist at all were it not that nature allowed a small violation of what is known as charge symmetry. This violation also causes the neutron, one of the constituents of atomic nuclei, to be slightly heavier (0.1%) than its charged partner, the proton. The rate at which this rare process occurs is expected to be a key piece of information that will point scientists toward the cause for this violation of charge symmetry. It has been proposed that this violation originates with quarks, the small particles that are found inside protons and neutrons. The rate will tell scientists how much of the violation comes from the fact that quarks carry small electrical charges, and how much comes from difference in the mass of the two types of quarks found inside neutrons and protons. Researchers focused a beam of heavy hydrogen onto a target of the same material. Sensitive detectors tracked the helium nuclei and captured the two photons that result when the pion decays. The team worked around the clock for two months, seeing at most only 5 of the rare events per day. However, the several dozen events collected will be enough to allow scientists to test their theories about the violation of charge symmetry. (Paper C3.003; contact Ed Stephenson, stephens@iucf.indiana.edu). At session C3, Allena Opper (Ohio University) will discuss another important new measurement of charge-symmetry breaking, at the TRIUMF facility in Canada (C3.002), and Jouni Niskanen of the University of Helsinki will describe new theoretical insights into the effect (C3.001).

HIGH ENERGY PHYSICS
The Philadelphia meeting coincides with the annual gathering of the APS Division of Particles and Fields, so there is a larger than usual collection of papers devoted to fundamental research conducted at the very highest energy. What are hot topics in particle physics right now? The study of "CP violation," essentially the subject of why matter and antimatter are not quite the same (sessions B1, C11, H11). Higgs bosons, the particles thought to endow other particles with mass (P14, P4, T12). Neutrino oscillations and neutrino mass (B13, P13, U1). The pursuit of "supersymmetric" particles, a hypothesized family of particles with counterparts to all the known particles (B12). Superstring theory, which attempts ambitiously to unify all the known physical forces within a single model (C6; Brian Greene, author of "The Elegant Universe," is the first speaker). The possibility of building a huge electron-positron linear collider (C1, F1) or a muon collider (R11). Searching for new effects beyond the standard model, including topics like extra dimensions, dark matter, and time-varying fundamental constants (H1).

SPEED OF GRAVITY?
A recent controversial measurement claimed to measure the speed of gravity by looking at the gravitational lensing of a star by Jupiter. While there is no doubt that this is an impressive experiment, the interpretation of the claim that the speed of gravity can be extracted from the results is very controversial. Clifford Will, of Washington University, St Louis, one of the leading experts in gravitational physics, will speak at the APS April meeting about his analysis of the problem. His research indicates that the experiment is not able to measure the speed of gravity in its current form and that the interpretation by Sergei Kopeikin and Ed Fomalont is flawed. (Session R12.001)

TELESCOPES OF ICE
Burying string-of-pearl detectors kilometers deep in Antarctic ice does not sound like the usual way to make a telescope. However, that is exactly what is currently happening in the AMANDA neutrino telescope. Steven Barwick, of the University of California, Irvine, will report on the latest results from the AMANDA project and also discuss the upcoming ANITA experiment. ANITA uses Antarctic ice, without anything embedded in it, to form the detector for neutrinos. Instead, the impacts of neutrinos are measured by an orbiting satellite looking back down at the ice. The earliest trials of this scheme will be based on high-altitude balloons rather than satellites and are to be launched in December. Barwick will also report on the next generation of the AMANDA detector and how it will be used to search the skies for gamma ray bursts. (Session P9)

DISARMAMENT GOES BALLISTIC
Approved by the United Nations in 1996 with only three opposing votes, the Comprehensive Test Ban Treaty (CTBT) enjoys near-unanimous support by the international community. But now that India is considered a "threshold nuclear nation", it must approve the treaty if it is to enter into force, and India's U.N. representative has said the country will never sign the treaty. Ram Chaturvedi (SUNY College at Cortland) will provide an overview of the treaty's current status, including India's continued refusal to ratify it. Meanwhile, on Tuesday morning speakers will provide an overview of the current status and future prospects for the U.S. ballistic missile defense programs, focusing on both mid-course and boost-phase technologies. (Sessions H8, T5)

ULTRA-HIGH-ENERGY COSMIC RAYS
A field currently exciting much interest concerns the observations of ultra-high energy cosmic rays and could imply new physics that we don't yet understand. This is often discussed in terms of the GZK (Greisen-Zatsepin-Kuzmin) limit, an expected upper limit on the energies of cosmic rays due to their interactions with the cosmic microwave background. One experiment (AGASA) indicates the existence of cosmic rays above this limit and physicists are wondering how to explain it. Eli Waxman (Weizmann Institute of Science, Israel) and John Bahcall (Princeton University) will claim that the GZK limit remains intact and that more prosaic explanations than the invention of new physics are enough to explain observations. As such, they will argue that the Pierre Auger Observatory under construction in Argentina would be better off searching in a different energy range to that currently planned, to make the best use of resources (Session F2.003). Other presentations (Session P3) will delve into the details of how these ultra-high energy cosmic rays are created in the first place. Pasquale Blasi, (INAF/Istituto Nazionale di Astrofisica, Italy) will discuss how an International Space Station experiment starting 2008 will use the Earth itself as a detector for ultra-high energy cosmic rays.

SEARCHING FOR TIME REVERSAL VIOLATION
The Standard Model, the reigning theory of matter and energy at fundamental scales, portrays a sub-microscopic world that works almost exactly the same whether viewed in forward or reverse time. However, the imbalance of matter over antimatter in the universe suggests that the microscopic world looks slightly different in forward and reverse motion--a situation known as time reversal (T) violation. The Standard Model allows for T violation, but at a level approximately a billion times too small to explain the asymmetry in matter vs. antimatter. Thus, producing a better limit on T violation will provide new details of physics beyond the Standard Model. One such experiment trying to accomplish this is the "emiT" experiment at Maryland's NIST Center for Neutron Research, in collaboration with several universities and colleges. The researchers detect about 30 neutrons per second undergoing beta decay, in which a neutron decays into a proton, an electron, and an antineutrino. Relative to the spin of the neutron, the researchers observe the directions of electron and proton momentum to define "right-handed" and "left-handed" decays. An imbalance in the number of left-vs-right-handed decays provides evidence of T violation. The researchers are looking for an asymmetry in left-vs-right handed decays at a level of one part in ten thousand. If they do, it will be a clear sign of physics beyond the Standard Model and will help theorists in developing more complete models of the universe. Currently the emiT collaboration has produced the best constraint on T violation in neutron decays, and the researchers think they will do about 7 times better in a second run that's currently underway. (Paper K8.001; Pieter Mumm, University of Washington, pieter@u.washington.edu)

TIME-VARYING FUNDAMENTAL CONSTANTS?
In talk C3.004, Ken Nollett of the University of Washington (nollett@yojo.phys.washington.edu) will tie together three seemingly unrelated but intimately connected topics in physics: (1) the reason for the small difference in mass between the proton and neutron; (2) the production rates of light elements in the early universe; and (3) the possibility that the inherent strength of the electromagnetic force has changed slightly over time. Researchers observing very distant gas clouds have suggested the final idea, of a changing electromagnetic force. However, Nollett will explore this hypothesis from a nuclear-physics angle: namely, how would a slightly different value of fundamental electric charge have affected the production of deuterium, helium, and lithium in the moments after the Big Bang? Basically, the fundamental value of electric charge determines the degree of repulsion between nuclei, which in turn influences the rate at which nuclear reactions take place. In addition, Nollett and colleague Robert Lopez, formerly of Cambridge University, have considered more subtle effects, such as the way in which the value of fundamental charge influences how strongly nuclei interact with photons. Based on these calculations, Nollett and Lopez can constrain how much the size of fundamental electric charge has changed since the universe was one second old. Their result is consistent with no change at all and implies that a difference larger than about three percent is unlikely. Moreover, altering the fundamental charge changes the size of the slight mass difference between the proton and neutron. The size of this difference has a large influence on the amount of helium made in the Big Bang, but it is difficult to compute based on the present understanding of subatomic particles.

FUSION PHYSICS
The April meeting will be one of the best places to learn about the latest developments in fusion energy research. Earlier this year, the US announced its decision to rejoin ITER, the international project to build a next-generation fusion energy reactor. Stewart Prager of the University of Wisconsin (scprager@facstaff.wisc.edu) will present the new strategy for achieving practical fusion power with magnetically confined fuel and show how it results from improved understanding of magnetic confinement physics. (F1.003) At sessions C10 and R6, 17 papers will address many of those aspects of magnetic confinement fusion physics where the recent advances have been most interesting and important. Not to be outdone, other approaches to fusion power are making significant progress. Sessions B4 and H6 feature the latest advances in inertial confinement fusion, in which a fuel pellet is compressed by energy or particles to extremely high densities, to the point at which the pellet becomes hot enough and dense enough to initiate energy-producing fusion reactions.

LANDMINES
Antipersonnel landmines left over from previous conflicts cause a great deal of human suffering, and while the issue has only recently received significant public exposure, the U.S. has been investing in research to detect and defuse landmines since World War II. In a Saturday afternoon session, speakers will provide an overview of the topic, covering approaches aimed at detecting the casing of landmines, and those aimed at directly detecting the explosive contents. Some techniques to be discussed include electromagnetic induction, acoustics, ground probing radar, trace explosive vapor detection, and nuclear quadrupole resonance. For example, Caltech's Nathan Lewis will describe recent results in exploiting vapor detection technology to make a low power, low cost "electronic nose", while Surajit Sen (SUNY-Buffalo) will describe efforts to apply impulse-based imaging to detect and image small non-metallic mines. (Session C2)

MEASURING THE NEUTRON LIFETIME
Sergei Dzhosyuk of Harvard (sergei@jsbach.harvard.edu) will describe a novel method for measuring the lifetime of a free neutron--the mean time it exists before it decays into proton, electron and antineutrino. The neutron lifetime--presently known to be 14 minutes, 45.7 seconds, plus or minus 0.8 seconds--is important for not only understanding the electroweak force, but also for calculations of the amount of light elements created after the Big Bang. A more precise value of the neutron lifetime will allow a better understanding of the initial moments in the life of the universe. The researchers confine neutrons in a magnetic trap, thus preventing them from interacting with the walls of the chamber, where neutrons can be absorbed or escape in some other way. The chamber is filled with superfluid helium cooled to 250 mK which allows neutrons to travel unimpeded, held only by the magnetic force. When a neutron decays, a flash of light is produced in the helium by the electron passing through. This light is a signature of a neutron decay and researchers can judge how long a neutron lives by the frequency of these flashes. Although their result is not, at the moment, more accurate than that of previous measurements, magnetic traps may present a much better system for such studies. Ultimately it should allow an improvement in measurement of the neutron lifetime by more than a factor of 10. (K8.002)

PARTICLES AND ASTROPHYSICS
Truly joining up the physics of the very small and the very large is the subject of particle astrophysics. In session T1 Max Tegmark (Pennsylvania) will report on the latest precision-cosmology data provided by the Microwave Anisotropy Probe (MAP) and the Sloan Digital Sky Survey (SDSS); Saul Perlmutter (UC Berkeley) will survey recent supernova observations, how they bear upon the subject of the acceleration of the big bang expansion, and how this effort will be aided by the future Supernova / Acceleration Probe (SNAP) craft. Other topics here include astrophysics as glimpsed at very high energies: x-ray, gamma-ray, and cosmic-ray observations.

SIGNS OF QUANTUM GRAVITY
The elusive unification of quantum physics with general relativity is not yet here but tantalizing signs of their union are beginning to appear. A session devoted to the phenomenology of quantum gravity (Session F2), will explore a range of issues, from the possible breakdown of special relativity, through to the most precise tests yet of gravity on small scales. Alan Kostelecky (Indiana University) will discuss possible extensions to the Standard Model of particle physics, the tight constraints on such extensions and how experiments can be used to find any deviations. Two groups will look at small scale tests of conventional Newtonian gravity, thereby providing the tightest bounds yet on the influence of quantum gravity or extra-dimensional effects. Gerald Gabrielse (Harvard University) will discuss how the recent trapping of cold antihydrogen will be used to test one of the most fundamental properties of nature, CPT symmetry.

THE FUTURE OF X-RAY AND GAMMA ASTRONOMY
The next five years will see the development of new probes of high-energy light in the universe. The five new projects to be discussed are: Swift, a gamma-ray bursts explorer; the Constellation X Observatory; the X-ray Evolving Universe Spectroscopy Observatory (XEUS) ; the Energetic X-ray Imaging Survey Telescope (EXIST); and the Gamma-ray Large Area Space Telescope (GLAST) (Session R4).

ACCELERATOR APPLICATIONS IN MEDICINE AND INDUSTRY
Beams of particles and high-energy light are used in undertaking basic research, but also can be applied in very useful, indeed life-saving, ways. Topics at session U2 include the use of neutron beams (Thomas Mason, Oak Ridge), the production of medical radioisotopes, Yves Jongen, Ion Beam Applications), food irradiation with electron and x-ray beams (Bruce Miller, SureBeam Corp.), the use of beams in radiation oncology (Alfred Smith, Univ. Texas Anderson Cancer Center), and synchrotron light (Erik Johnson, Brookhaven).

MEASURING BEAUTY
A major factor in about half of automobile purchases is the outward appearance of the car. In many aspects of life, appearance plays a significant role lin choices we make. How do producers insure that their products satisfy the somewhat fickle eyes of buyers? NIST scientist Maria Nadal will speak about the development of appearance metrology, the precision measurement of appearance. Some of the techniques include analysis of gloss levels and color appearance (Session B5).

Also contributing to this press release were Phillip Schewe of AIP and Jennifer Ouellette of APS.

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