New Research in Particle, Nuclear and Astrophysics Featured at April Meeting
Three plenary sessions (A1, Q1, W1) will spotlight eminent speakers holding forth on the leading topics of the day. Francis Everitt (Stanford) will present new results form the Gravity Probe B mission. Allan MacDonald (University of Texas) will describe the amazing properties of electrons moving about in a two-dimensional graphene sheet. Gerald Gabrielse (Harvard) will discuss his new measurement of the electron’s magnetic moment, which resulted in a new value for the fine structure constant. David Spergel (Princeton) will review the implications for cosmology of the WMAP mission, which provided recently such a fine map of the cosmic microwave background.
LBL Director Steven Chu will discuss the role played by physicists in the development of clean energy sources. Shamit Kachru (Stanford) will look at how string theory addresses the idea that many universes might exist simultaneously, each with its own fundamental “constants.” Jacqueline Hewitt (MIT) will speak about the early “dark age” in the universe; James Hansen (NASA Goddard Institute for Space Studies) will discuss global warming and its possible side effects; and Steven Vigdor (Indiana) will report on recent proton spin results from the Relativistic Heavy Ion Collider (RHIC).
Putting a Spin on the Proton. The Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory has been taking a break from its experimental efforts to re-create the conditions of the early universe. During the past year, RHIC has been investigating the origin of the proton’s spin, the property that gives the proton its internal magnetism. The origin of this spin remains a mystery. The proton gets only about 25% of its total spin from its quarks (which include not only its three main “valence” quarks but also the quark-antiquark pairs that blink in and out of existence inside the proton’s confines). The remaining 75% might come from the proton’s gluons, which hold together the quarks and from orbital motions of quarks and gluons in the proton. With help from the RIKEN Institute in Japan, RHIC has been converted part-time into the world’s only collider of proton beams with spins that are “polarized” or pointed in desired directions. Nuclear physicists at RHIC are now studying the aftermath of high-energy proton-proton collisions to infer the role of gluons and of orbital quark motion in building the proton spin. RHIC collaborator Steven Vigdor of Indiana University will present preliminary experimental results on these investigations. (W1.3)
Photo courtesy of NASA
Gravity Probe B satellite in space
However, physicists are concerned that high-energy-physics collaborators in developing nations might not have access to the large bandwidths needed to handle the huge amounts of data from the collider. Presenters in two sessions (M10 and R9) will discuss efforts to reduce this digital divide. Harvey Newman of Caltech will present an introduction to this problem as well as the findings of a major new report exploring this issue. Other talks will present programs to close the digital divide in Latin America (R9.1), South Africa (R9.3), India (M10.3) and Pakistan (R9.4), and the building of a “Virtual Silk Highway” (R9.2) that has brought about fast communications networks to Afghanistan and eight Former Soviet Republics.
Gravity Probe B. Stanford University’s Francis Everitt will outline the preliminary results of the $750 million Gravity Probe B mission, possibly the longest-running, most expensive single experiment in history. GP-B is a NASA mission first envisioned in the early 1960s and launched in April 2004. It aims at directly measuring a subtle effect of Einstein’s general relativity for the first time. The effect, called frame dragging, is a distortion of space caused by Earth’s rotation around its axis, which is expected to deflect the spinning axis of a gyroscope by such a small angle that it would take more than a million years for the gyroscope to turn in a full circle. Following several more months of data analysis, the GP-B team expects to announce its final results by the end of the year.
Northern (Galactic Pole) Exposure. Researchers have combined data from the Arecibo radio antenna in Puerto Rico and the Dominion Radio Astrophysical Observatory interferometer in Canada to produce a stunning view of the sky above the plane of our galaxy. In particular, the image shows a surprising lack of correlation between the faint radiation produced by particles accelerated in the magnetized plasma of space and the distribution of bright stars and galaxies in the nearby universe. The work also offers insights into the origin and nature of some cosmic rays, into how intergalactic ultra-high energy cosmic rays might propagate, and provides a preview of the Galactic and extragalactic features that might contribute to the cosmic microwave background (CMB) on scales to be imaged by the PLANCK CMB Explorer, which NASA and the European Space Agency are jointly planning to launch later this year. Philipp Kronberg (Los Alamos National Laboratory) will present the images resulting from the combined radio data, as well as other insights to come out of the project (H11.4).
New Atomic Effect. Recently, Rudolf Grimm of the University of Innsbruck and his colleagues provided the first experimental demonstration of an atomic phenomenon, first predicted in 1969, known as the Efimov effect. An entire session, B8, will be devoted to this newly observed phenomenon. In the Efimov effect, two atoms which usually repel each other become attracted when a third atom is introduced. The trio can then form an infinite number of “bound states,” or energy states in which the atoms are stuck to one another. Atoms entering the Ekimov state veer from their chemical behavior; they behave differently in the company of two other atoms. Grimm will describe his collaboration’s experimental demonstration, which involved cesium atoms cooled to ultracold temperatures of just nanokelvins. Also speaking will be the University of Colorado’s Chris Greene, who predicted with a coauthor that ultracold atomic gases would be the ticket to observing this elusive effect. Paulo Bedaque of the University of Maryland will describe how the Efimov effect at the scale of the nucleus can provide insights into the theory of nuclear forces.
The Life of Pion. In efforts to better understand how the universe evolved into a place with distinct particles and forces, researchers at the U.S. Department of Energy’s Jefferson Lab have been performing the Primakoff Experiment (PrimEx). PrimEx is making new precision measurements of the lifetime of a short-lived subatomic object known as the chargeless pion, which can be imagined in simplest terms as a quark-antiquark pair. Before it decays into other particles, the chargeless pion exists for only an attosecond, a thousand times shorter than predicted by early particle theory. Newer theories come closer to this observed result by taking into account chiral symmetry breaking, a phenomenon in which a configuration of nuclear particles and its mirror image do not always behave as mirror images of one another even when researchers perform identical experiments on them.
In PrimEx, researchers aim a photon beam at a nucleus, which perpetually has a cloud of photons around it. Two photons–one from the nucleus and another from the photon beam–interact and make a chargeless pion, which decays into two photons. Measuring the photons provides lifetime information on the pions, with the ultimate goal of obtaining more information on the process of chiral symmetry breaking. Ashot Gasparian of North Carolina A&T State University will present the latest results on PrimEx. (B2.1)
Putting Newton to the Test. Newton’s laws break down at some point, giving way to quantum mechanics under some circumstances and relativity at others, and perhaps even yielding to some as yet unknown physical laws somewhere along the way. But just where Newtonian physics crumbles isn’t clear. As a result, many researchers have dedicated themselves to tracking down the limits of classical dynamics. Several groups report in session K12 on their efforts to put Newton to the test by searching for unusual gravitational effects at distances below a millimeter; measuring the distance to the moon with millimeter precision via laser ranging; and testing to see if Newton’s second law, F=ma, holds when accelerations and forces are extremely small. There’s no sign that anyone has succeeded in pinning down the precise limits to Newtonian physics, but all the testing is helping to eliminate exotic theories that attempt to explain away things like dark matter. The experiments are also often the source of new records in precision measurements of fundamental physical laws.
Cosmic Causes of Terrestrial Biodiversity. The diversity of creatures crawling, flying, and swimming across our planet may stem in part from the motion of the solar system through the galactic plane because the radiation that reaches Earth varies as a result of our location in the galaxy. The fact that episodes of large scale extinctions on the planet seem to match the 62 million year cycles of the solar system’s motion suggests that evolution may be driven by fluctuations in the radiation that Earth receives. In a series of papers (E11.6, E11.7, and E11.8), University of Kansas researchers Bruce Lieberman, Mikhail Medvedev and Adrian Melott investigate several kinds of astrophysical radiation sources that affect life on Earth, generalizing their earlier computations to improve their insight into the effect of the radiation on the atmosphere. Among other results, they have found that the duration of the radiation exposure makes very little difference. From millisecond gamma ray bursts to 3-year increases in radiation, the ultimate amount of ozone depletion (and the resulting impact on species) is dependent primarily on the total amount of energy dumped in the atmosphere.
Physics Festivals and Fights. People in the general population don’t often go in search of science, so some physicists are taking science to the people. Brian Schwartz (Graduate Center of CUNY) will describe the outcomes of some creative science popularization efforts, including a city-wide science festival in New York last November and hands-on physics demonstrations at a New York City street festival in June of 2006 (B5.2). Hugh Haskell (North Carolina School of Science and Mathematics) is interested in a more rough and tumble physics educational effort–he works with the National Young Physicists’ Tournament (NYPT), which is modeled on a Russian physics competition started in the 1970s, but is new to the US. Groups of students involved in the tournament tackle a scientific question by developing a theoretical model to address it, performing an experiment to test their theory, and ultimately defending their work while critiquing the research of other groups. The top team in the bare-knuckle physics competition goes on to battle students from 25 other nations in the international stage of the tournament. Haskell and colleagues believe the NYPT ultimately helps build both better physics students and better teachers (C10.1).
A Bit of Physics History. Max Jammer (Bar-Ilan University), a distinguished physicist and author of notable books about fundamental physical properties like mass and space, is the winner of the Abraham Pais Prize Lectureship. Unable to attend the meeting himself, his paper, on the subject of how our modern concept of time came to be (U6.2), will be read out at the session. How the standard model of particle physics came to be so standard will be the subject of Michael Riordan’s (UC Santa Cruz) talk in session E10. He contends that the crucial years were 1964-1979, when a series of decisive experiments and incisive theoretical work came together. Other historical talks of interest concern such topics as Albert Einstein’s trip to New York City in 1921 (R10.2), the Heisenberg uncertainty principle, early photons in the early universe (E10.5), and a history of arms control prepared by officials at the US State Department (R10.6). Session T6 looks at Sputnik, the 1950s, and the founding of NASA.
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Contributing Editor: Jennifer Ouellette
Staff Writer: Ernie Tretkoff