Physics News Update, Number 441

Number 441, July 30, 1999 by Phillip F. Schewe and Ben Stein

THE CHANDRA X-RAY TELESCOPE is now installed in its highly elliptical orbit, where the Earth itself, and not just its atmosphere, will not interfere with x-ray reception. Named for astrophysicist Subrahmanyan Chandrasekher, the 14-m-long telescope is considered one of NASA's three "great observatories"; the other telescopes in this battleship class are the Hubble Space Telescope and the Compton Gamma Ray Observatory. Chandra will have superb angular resolution (half an arc-second, 8 times better than previous x-ray telescopes), sensitivity to faint objects (20 times better), and spectral resolution (1 eV). The object of the mission is unflinchingly to explore graphic violence wherever it can be found at x-ray wavelengths: quasars, black holes, pulsars, supernovas, and intergalactic plasmas. (http://www1.msfc.nasa.gov/NEWSROOM/background/facts/cxoquick.htm)

BLOCH STATES: NOT FOR ELECTRONS ONLY It is often essential to consider an electron traveling through a solid as being a wave that spreads out through the whole of the solid. The quantum description of this spread-out electron was formulated by Felix Bloch in the 1920s. Physicists have since sought to extend this idea of a "Bloch state" to guest atoms in a crystal, but an atom's mass is so large (and its equivalent wavelength so small) that a Bloch state for an atom has been difficult to observe. Now, physicists from Japan (Ryosuke Kadono, KEK, ryosuke.kadono@kek.jp) have seen clear signs of a Bloch state for a muonium "atom", in effect a light isotope of hydrogen whose proton is replaced by a positively charged muon particle having 1/9 of the proton's mass. Performing experiments at the Rutherford Appleton lab in England, the researchers studied spin-polarized muonium (Mu) atoms in a KCl crystal cooled down to 10 mK. Measuring how long it took the atoms to lose their initial polarization in the presence of an external magnetic field provided information on their energy state and matched the predictions of a Bloch model. Further studies may offer new insights into the energy bands of atoms in crystals. (Kadono et al., Physical Review Letters, 2 August 1999.)

PARTICLE ACCELERATOR TURN-ONS The concrete poured and the magnets tuned, several important new machines are about to take up important physics matters. The Main Injector at Fermilab, dedicated in June, is an additional 2-mile racecourse for getting protons up to speed in much greater numbers. What this means is that the proton-antiproton collider run starting in 2000 will record in one year as much data as was taken in the earlier 10-year era. This is crucial since beam intensity is no less important than the energy of collision when producing rare objects, such as supersymmetric particles (hypothetical cousins of the known leptons and quarks) and the much sought Higgs boson (playing a sort of midwife role in the life of many other particles, the Higgs should also exist in its own right). New theoretical estimates for the mass of the Higgs suggest that Fermilab might just have enough energy to discover the Higgs (Science, 25 June). Meanwhile, two accelerator schemes dedicated to studying CP violation through the agency of B-meson decays, are nearly ready. The Asymmetric B Factory at SLAC in California is now smashing 9-GeV electrons into 3.1-GeV positrons to produce pairs of Bs. The decay products are absorbed in a detector called BaBar. A comparable setup at the KEK lab in Japan will soon collide 8-GeV electrons with 3.5-GeV positrons inside a detector called BELLE. By the way, the cost of these detectors is a not-inconsiderable portion of the accelerators themselves. BaBar and BELLE cost, respectively $80 million and $70 million (Physics World, May 1999). Finally, at the DAFNE electron-positron collider in Frascati, Italy, CP violation is also the subject matter, but the approach is different. Here the collisions are dedicated to making phi mesons, which then decay into a pair of K mesons, which in turn break up (amid the KLOE detector) in a process that violates charge-parity invariance (CERN Courier, June 1999.)