Physics News Update No. 617

Physics Stories of 2002
The top two physics stories for the past 12 months were the total accounting of neutrinos from the sun by the Sudbury Neutrino Observatory (SNO), thus solving the solar neutrino problem (Update 586; www.aip.org/enews/physnews/2002/split/586-1.html); and the formation and detection of antihydrogen atoms at CERN (Updates 605 and 611, www.aip.org/enews/physnews/2002/split/605-1.html and www.aip.org/enews/physnews/2002/split/611-1.html ).

Other notable physics developments for the year include stopping and storing light in a solid (Update 571), the observation of phase-transition behavior in nuclei (572), publication of some unsent letters by Niels Bohr to Werner Heisenberg (576), interferometry with C-70 molecules (579), a dispute over "fusion" in sonoluminescence (579, 599), most precise tests of special relativity (571, 590), sharper maps of the cosmic microwave background (591), "droplet" of light (596), claims for element 118 retracted (597), verification of the notion that the second law of thermodynamics can be violated on small spacetime intervals (598), high precision measurements of CP violation in B meson decays and in the g-2 factor of the muon (600), scandal at Lucent (606), record high laboratory magnetic fields (614), polarization in the cosmic microwave background detected (606), 2002 Nobel prize for physics (608), noise can improve balance (612), and longest measured atomic lifetime (616). All the above Update items can be retrieved from our archive at www.aip.org/physnews/update.

Reactor Anti-Neutrino Disappearance, measured by a detector in Japan, supports the idea that neutrinos oscillate from one type to another and that they possess mass. Nuclear reactors produce several things: heat, electricity, spent fuel rods, and neutrinos. The neutrinos (or, to be more exact, electron anti-neutrinos) are a result of fission reactions inside the reactor core. But some of the electron antineutrinos, once they're underway and moving through the Earth, manifest one of the weirdest phenomena in all of physics, namely the ability to exist as a composite of several sub-species. That is, what we call a neutrino is really several (perhaps three) neutrinos in one.

At any point along its trajectory the generic neutrino might (if you were to capture it just then) appear as an electron neutrino, but farther along it might look like a muon neutrino, in which case it would elude detectors tuned to detect only electron nu's. The Kamioka Liquid Scintillator Anti-Neutrino Detector (KamLAND) sets out to sample this odd mode of being. The apparatus, basically a huge reservoir of optically-active liquid viewed by numerous phototubes, looks for interactions in which an incoming nu strikes a proton, creating in their stead a trackable neutron-positron pair. KamLAND resides in an underground lab beneath Toyama, Japan. It is a sort of telescope peering not at galaxies in the sky; instead it stares through a block of terrestrial crust looking for the neutrino warmth cast off by a constellation of 69 reactors in Japan and Korea.

Taking into account the laws of physics governing the reactions in the reactor cores, the known power ratings for the reactors, their aggregate reactor-detector distances, and the duration of the experiment (145 days), one would expect seeing 86 true events, whereas the actual number was 54. The researchers conclude that the disappearance of events is due to neutrino oscillation. This result is not merely a confirmation of oscillation research carried out with solar nu's at such detectors as Super Kamiokande in Japan and the Sudbury Neutrino Observatory (SNO) in Canada (see Update 586, http://www.aip.org/enews/physnews/2002/split/586-1.html). For one thing KamLAND studies anti-neutrinos rather than neutrinos. Furthermore, the production of neutrinos in a reactor is much closer at hand and better understood than is the case for the sun. The KamLAND finding also serves to narrow the theoretical explanation of the neutrino's split personality. (Eguchi et al., paper submitted to Physical Review Letters, text and background information at: http://hep.stanford.edu/neutrino/KamLAND/KamLAND.html)

Schematic of a chip designed to study the flow of ions in and out of cells through single proteins. An electrolytic solution on both sides of the chip is electricallly contacted via electrodes. (A) The measured current response to a voltage pulse of 10 millivolts. (B) The same voltage pulse is applied after a cell is sealed onto the aperature by suction. (C) Closeup shows the mechanically and electrically tight contact of the cell membrane. (Courtesy of CeNS)

Ion-Channel Proteins, which act as a sort of circuit element, allowing the flow of ions in and out of cells, can now be scrutinized in a new way that exploits technology operative at the single-molecule level. Scientists from the Center for NanoScience (CeNS) at the Ludwig-Maximilians-University in Munich don't make electrical contact with cells in the customary way by pressing an electrolyte-filled glass micro-pipette against the cell membrane. Instead they allow individual cells to settle down onto a glass gasket covered with micron-sized pores, allowing the ion-channels to protrude out the bottom. This chip-based architecture, the researchers believe, will more easily facilitate an automated biotech-nanotech approach to ion-channel research, which in turn is important for understanding how cells exchange information in various nervous, cardiovascular, intestinal, and reproductive processes. (Fertig et al., Applied Physics Letters, 16 December 2002)

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