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Number 405, December 7, 1998 by Phillip F. Schewe and Ben Stein
INTRIGUING INDICATIONS OF CP VIOLATION IN B MESONS has turned up at Fermilab. CP is the abbreviation for the compound operation which turns a particle into an antiparticle (charge conjugation, or "C") and then sends the particle through a 3-dimensional looking glass (parity reflection, or "P"). A 1964 experiment unexpectedly showed that particles do not necessarily behave the same before and after the CP operation. Because CP violation is thought to account for the apparent fact that matter far outweighs antimatter in the universe physicists are eager to explore the issue further. So far CP violation only has been observed in the decay of K mesons, which contain rare s (or strange) quarks. Physicists suspect that the mysterious CP violation will also have a role in the decay of B mesons, which contain the ever rarer b (or bottom) quark. To settle this issue, B factories, dedicated electron- positron colliders that will do nothing but produce B mesons, are being built at Stanford and in Japan and elsewhere. But B mesons are already being produced in large numbers at Fermilab. The trouble here, however, is that in proton-antiproton smashups the number of B's produced is vastly outnumbered by other particles. Nevertheless, the CDF collaboration (Gerry Bauer, bauerg@fnal.fnal.gov, 630-840-8621) has painstakingly isolated a number of events in which B's decay into a K meson and a psi meson. The data analysis can even tell a B from an anti-B meson, and the observed asymmetry in their production is what gives a very tentative indication (based on a modest amount of data) that CP violation is occurring in B mesons. The Fermilab physicists are confident this matter can be pursued at proton machines, especially with Fermilab's much intenser beam, which will be in effect by the spring of 2000. The Stanford B factory should be running a year before that. (Abe et al., Physical Review Letters, 21 December 1998; reporters can obtain a copy from AIP Public Information.)
A "PERFECT MIRROR," one that efficiently reflects a specified wavelength range of light coming in from all directions, has been built by MIT researchers (Yoel Fink, 617-253-8454), opening possibilities for energy-saving windows and better versions of optical fibers for telecommunications. Traditional metallic mirrors can reflect a wide range of colors from all directions, but they typically absorb a few percent of the light that strikes them. More recent "dielectric mirrors" (which consist of alternating layers of insulating materials) are highly reflective, but they work only for a narrow wavelength range of light hitting them straight on. Combining the best properties of both mirror types, the MIT group designed a dielectric mirror consisting of 9 alternating, micron-thick layers of the element tellurium and the polymer polystyrene. The highly contrasting indices of refraction in these layers enabled light (10-15 micron wavelength, in the infrared) coming in from all directions to be reflected at the interfaces. In addition to practical applications, the researchers speculate that this design might allow physicists to confine light for longer amounts of time than previously possible. (Fink et al., Science, 27 November 1998.)
THE MARS GLOBAL SURVEYOR laser altimeter, with its 30-cm precision, is rendering the best topographic maps yet for the red planet. Two highlights from a series of articles in the 15 December issue of Geophysical Research Letters---Mars is less flattened than was thought: its mean equatorial and polar radii are measured to be 3396 and 3373 km; and a possible shoreline of a presumed ancient polar ocean was studied.
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