SETI Physics News Update.435


Larry Klaes (lklaes@bbn.com)
Tue, 22 Jun 1999 00:24:42 -0400


>Date: Mon, 21 Jun 1999 14:04:35 -0400 (EDT) >From: AIP listserver <physnews@aip.org> >To: physnews-mailing@aip.org >Subject: update.435 > >PHYSICS NEWS UPDATE >The American Institute of Physics Bulletin of Physics News >Number 435 June 21, 1999 by Phillip F. Schewe and Ben Stein > >HELIUM-6 NUCLEI SHARE DI-NEUTRONS. Helium-6 nuclei, >formed into beams for the first time only last year, are thought to be >"Borromean" structures (so named for the heraldic symbol of the >Princes of Borromeo, and consisting of three interlinking rings which >fall apart if any one ring is removed). The He-6 nucleus, theorists >believe, is really a He-4 core surrounded by two extra, loosely bound >neutrons which can reside in one of two configurations: (1) one >neutron on either side of the He-4 core or (2) both neutrons close >together (comprising a "di-neutron") far from the He-4 core. To test >this theory and to demonstrate the existence of di-neutrons, Yuri >Oganessian and his colleagues at the Joint Institute of Nuclear >Research (JINR) near Moscow (oganessian@flnr.jinr.ru, 011-7- >09621-62151) collided a He-6 beam with a He-4 target and observed >that some of the He-4 nuclei had been converted into He-6, proving >that in some of the high-energy collisions di-neutrons had jumped >from one nucleus to the other. This also holds true when He-6 beams >hit hydrogen targets (the target nucleus being a single proton). In this >case a di-neutron joined the proton to form a tritium nucleus. These >results seem to favor the picture in which di-neutrons are the rule >rather than the exception in He-6 nuclei. Now the JINR scientists are >using He-8 beams to study in more detail how neutrons correlate with >each other within nuclei and to search for signs of "tetra-neutron" >states. (Oganessian, Zagrebaev, and Vaagen, Physical Review >Letters, 21 June 1999; figures at www.aip.org/physnews/graphics) > >DETECTION OF EARTH'S MAGNETIC FIELD USING >NEUTRINOS has been accomplished at the Super-Kamiokande >detector located underneath Mt. Ikenoyama in Japan. Here is the >sequence of events: a cosmic ray proton strikes an oxygen or nitrogen >atom in Earth's upper atmosphere, creating a neutrino which passes >freely into the Earth where it may find its way into Super- >Kamiokande, a device consisting chiefly of 50,000 tons of pure >water. In the water the neutrino (when it bothers to interact at all) >will typically convert into a muon or electron, plus light, which is >recorded in surrounding photodetectors. In this process, the neutrino >and its daughter muon or electron track pretty closely the trajectory of >the original cosmic ray proton. But the incoming cosmic ray flux, >which would otherwise be isotropic, is shaped by the Earth's >magnetic field. This acts as a sort of prevailing wind which sets up >an east-west anisotropy in cosmic rays. This anisotropy, measured as >long ago as the 1930s, should be matched by a corresponding >anisotropy in neutrinos, which is precisely what the Super- >Kamiokande team now finds. This measurement, while it says >nothing new about Earth's magnetic field, does reassure the >researchers that their detection of neutrino oscillation (one of the top >physics stories of 1998, see Update 375) stands on a firm >understanding of the complex chain of events whereby a cosmic ray >in outer space leads to a burst of light in a cavern beneath Japan. >(Futagami et al., Physical Review Letters, 28 June 1999; team leader, >Y. Totsuga, totsuga@suketto.icrr.u-tokyo.ac.jp, Tokyo University; >some US contacts: Henry Sobel, UC Irvine, 949-824-6911, >sobel@uci.edu; Lawrence Sulak, Boston University, 617 353- 9454, >sulak@bu.edu; paper available to science writers from AIP public >information; www.aip.org/physnews/graphics) > >DIRECT CP VIOLATION AT CERN. The NA48 experiment at >CERN reports a new detection of direct CP violation (partly >responsible for the slight asymmetry between matter and anti-matter) >in the decay of K mesons. The value they measure for the ratio >epsilon prime over epsilon (roughly the ratio of direct to indirect CP >violation see Update 420) is 18.5 +/-7 x 10^-4. The value reported >by a Fermilab group earlier in the year was 28+/-4 x 10^-4. >(http://www.cern.ch/Press; for background see Physics Today, May >1999.) >



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