Number 218, March 17, 1995 by Phillip F. Schewe and Ben Stein CPT CONSERVATION, SPECIAL RELATIVITY AND THE SINGLE ANTIPROTON: Gerald Gabrielse (617-495-4381) of Harvard and his colleagues can adjust the electrical voltages of their tabletop antiproton trap at CERN to remove antiprotons until only a single one remains. Measuring a single antiproton, without the perturbing influences of many particles, not only improves precision in measurements of its charge-to-mass ratio but also allows the effects of special relativity to become manifest. The rate at which the circulating antiproton completes an orbit around the trap, known as the cyclotron frequency, is equal to the product of magnetic field strength and its electrical charge divided by its mass. In separate measurements of a single proton in their trap, they confirmed that the cyclotron frequency of antiprotons and protons is identical to one part in a billion--a factor of 40 improvement over their previous measurements involving many trapped particles and 45,000 times more precise than earlier measurements with hot antiprotons. Not only does this measurement confirm that proton and antiproton masses are equal to a new level of precision (assuming that they have the same magnitude of charge), but it stringently tests the CPT theory, which holds that the outcome of one experiment involving a set of particles is identical to a time-reversed mirror image of the experiment in which all of the particles are replaced by their antiparticles. This is the first exact test of CPT theory for baryonic matter (precision tests of the PCT theorem have already been performed for leptons and pions). In separate measurements, the researchers then applied a brief radio pulse to add energy to the antiproton, increasing its velocity and consequently its mass according to special relativity. As the antiproton dissipated this energy in the trap, the researchers observed an increase in cyclotron frequency, signalling a decrease in the mass. (G. Gabrielse et al., 1 May in Physical Review Letters.) THE IMPRINT OF COMET SHOEMAKER LEVY on Jupiter has faded but the events surrounding the explosive encounter of July 1994 are relived in a suite of nine papers in the 3 March issue of Science. Some of the highlights are as follows: G. Orton et al. describe infrared observations, made with the NASA Infrared Telescope Facility, which suggest that after the impacts the abundance of stratospheric ammonia increased by a factor of 50 and that the north polar aurora brightened by a factor of 5 in the near infrared. H.A. Weaver et al., analyzing images made with the Hubble Space Telescope (HST), allow that there is still considerable uncertainty in the size of the largest fragments; estimates go as high as 4 km, but a size of less than 1 km cannot be ruled out. H.B. Hammel et al. report that the impacts were on average about eight minutes later than expected. Robert A West et al. suggest that the brown color of the debris particles comes from sulfur- and nitrogen-rich organic matter. In the core regions of the impact sites, the particles had a radius of 0.15 to 0.3 microns; later they coagulated into larger clumps. K.S. Noll et al. used ultraviolet spectra to identify several molecules never seen on Jupiter before, such as S2. Some scientists had suspected that the passage of charged cometary dust through the Jovian magnetic field would, through a sort of dynamo effect, trigger auroral emissions. Just such a display was observed in the far ultraviolet by R. Prange et al. Finally, James R. Graham et al. used the prodigious light-gathering power of the Keck Telescope to produce an infrared movie (7.7 sec per frame) of the fragment R collision. At its peak the resulting flare from the impact outshone Jupiter itself.