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| Issue 12, 2024 |
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Extracts from the Internet | ||
Unusual meson2 December 2007In recent years experiments at Belle and ÂàÂàã revealed several mesons such as Õ(3872), Y(4260), X(3940) and Y(3940) which do not comply with the conventional classification of mesons as their masses and decay characteristics are anomalous. According to one of the hypotheses, these mesons may be composed of four quarks. A new meson Z±(4430) discovered at the Belle collaboration\'s electron-positron collider (KEK Laboratory, Japan) among the decay products of B-meson decays is shown to have an electric charge, in contrast to other “anomalous” mesons. Among the 657 million pairs of BB mesons, 120 events were found that show decays in which Z±(4430) and K-mesons were created. Z±(4430) particles were identified from the resonance peak in the spectrum of decay products, their charge is 1e, the mass is 4.43GeV and they quickly decay to ψ' and π±. The statistical significance of the result is 6.5σ. The nonzero charge favors the four-quarks model and permits one to exclude the alternative interpretation of the Z±(4430) as an excited state of a two-quark c-anti-c meson. It is likely that the Z±(4430) consists of c, anti-c and two additional quarks, such as e.g. u and anti-d. Sources: arXiv:0708.1790v2, KEK:PRESS Release (BellePress) Neutrino beam from acceleratord detected2 December 2007Muon neutrinos generated at the CERN accelerator in Switzerland were aimed through the body of the Earth at the OPERA detector and detected there at a distance of 730 km at the Gran Sasso National Laboratory in Italy. The detector is installed inside a tunnel in a mountain; it is composed of 60,000 modules made of alternating layers of lead andnuclear emulsion film in which cascades of particles are created on interaction with neutrinos. Reaction products are studied by muon spectrometers. Nearly 300 accelerator-produced neutrinos have by now been recorded at Gran Sasso. As the size of the detector increases to 150,000 modules and further experimental data is gathered, plans are made to conduct a high-precision study of the effect of neutrino oscillations: the transformation of muon neutrinos into tau neutrinos and vice versa. The OPERA experiment is conducted by an international team comprising Russian scientists. Source: http://www.infn.it/news/newsen.php?id=441 New isotopes2 December 2007The NSCL laboratory of the Michigan University reported obtaining for the first time rare stable isotopes with neutrons in excess, 40Mg (12 protons and 28 neutrons), 42Al (13 protons and 29 neutrons), and also indications that the isotope 43Al was also produced. These isotopes were generated in collisions of a beam of 48Ca nuclei with a tungsten target; this was followed by complicated, multi-stage technique for separation and identification of rare nuclei. Three 40Mg nuclei, 23 42Al and possibly one 43Al nucleus were identified. A study of these nuclei is important for testing the theoretical models of nuclear physics, for instance for more accurate delineation of the boundaries of the domain of existence of nuclei on the N-Z diagram. The theory successfully predicts the neutron-rich nucleus 40Mg but encounters difficulties in explaining the stability of the nucleus 42Al against its decay since this nucleus falls outside the expected stability domain boundary (the neutron drip-line) on the N vs. Z diagram. The experimental discovery of the nucleus 42Al demands improvements in the theory. Source: Nature 449 1022 (2007) Cooper pairs in a dielectric2 December 2007The mechanism of Cooper pairing of electrons lies at the basis of the phenomenon of superconductivity. Ì.Stewart and coworkers at the Brown University in the USA found that Cooper pairs can under certain conditions arise also in dielectric materials. A layer of bismuth only four atoms thick was deposited onto a substrate with a number of holes provided along it, 50nm in diameter. This specimen was placed in a magnetic field and cooled to low temperature but still remained dielectric even though the electronic properties of the specimen showed that its conduction involved Cooper pairs of electrons. The holes in the substrate disturbed the rectilinear motion of charge carriers into vortical flow and thus blocked the formation of continuous lines of motion of Cooper's pairs and the transition to superconducting state. Source: physorg.com Record-mass stellar black hole2 December 2007A black hole with a mass of 15.7 solar masses was discovered in a binary system in the M33 galaxy using the Chandra Space Telescope and the Gemini telescope in Hawaii. The mass of this back hole is greater than that of any other known black hole formed by exploding supernovas. Owing to the fact that the black hole is eclipsed by its companion star every 3.5 days, it was possible to calculate the parameters of the orbits and the masses of the components of the system with fairly high accuracy, and the length of the eclipse yielded the radius of the star. The companion star is also exceptionally massive - approximately 70 solar masses. This discovery is at odds with the available models of binary star evolution which hold that in a binary system the mass of black hole of stellar origin cannot be so large. Before the collapse of one of the stars into the black hole, the two stars were close to one another and had a common atmosphere so that the binary system was inevitably losing mass quite rapidly. In fact, judging by the mass of the resulting black hole, the star was shedding mass prior to the explosion 10 times more slowly than is predicted by the theoretical models. Source: Chandra Press Room Sources of ultrahigh-energy cosmic rays2 December 2007Statistically significant (at 99% confidence level) correlation was detected of ultrahigh-energy cosmic rays detected by the Pierre Auger detector with the directions pointing to the positions of active galactic nuclei (AGN). Pierre Auger is an array of 1600 detectors covering an area of 3000 km² that record particles in cascades produced in the atmosphere by particles of cosmic rays. The Pierre Auger also includes optical telescopes for recording the Cerenkov radiation in the atmosphere generated by the same cascades. The direction of arrival of 27 detected particles with the highest energies (>5,7×1019eV) was compared with the catalog of AGNs. With the exception of eight such events, the position of cosmic rays on the celestial sphere coincided (to within the angular resolution of the detector) with the positions of galaxies. All these identified source galaxies are at a distance up to 75 Ìpc, which is in agreement with the limit imposed by the Greisen-Zatsepin-Kuzmin effect. Source: Science 318 938 (2007) |
The Extracts from the Internet is a section of Uspekhi Fizicheskih Nauk (Physics Uspekhi) — the monthly rewiew journal of the current state of the most topical problems in physics and in associated fields. The presented News is devoted to the fundamental discoveries of physics and astrophysics. Permanent editor is Yu.N. Eroshenko. It is compiled from a multitude of Internet sources. | |
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