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| Issue 11, 2024 |
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Extracts from the Internet | ||
Bottomonium ηb(1S)1 August 2008Radiational decays of resonances Υ(3S) → γηb(1S) that create bottomonium ηb(1S) in the lowest energy state were identified in the BaBar experiment conducted at the Stanford Linear Accelerator Center (SLAC). The family of particles with the quark composition b-anti-b (bottomonium) was discovered experimentally about 30 years ago (see Uspekhi Fizicheskih nauk 152 361 (1987) (in russian)) but the lightest of these mesons, ηb(1S), was detected for the first time. The particles in this family differ in several quantum numbers, including the sum of quark and antiquark spins S. The bottomonium ηb(1S) with 2S + 1 = 1 is a pseudoscalar spin-singlet partner of the Υ(1S) meson. The Υ(3S) resonances were created in e+e- collisions in the PEP-II storage ring where about 108 such particles were analyzed. The state ηb(1S) was identified using the peak in the spectrum of photons emitted in transitions of bottomonium from level Υ(3S) to ηb(1S). The confidence level of the result is about 10σ. The mass of ηb(1S) is lower than that of Υ(1S) by approximately 71.4 MeV, which is in good agreement with “lattice QCD” computations. The difference between the masses of ηb(1S) and Υ(1S) is the key quantity for many theoretical calculations and its measured value will help test models of interaction between quarks and will perhaps help establish a more accurate value of the strong interaction coupling constant αs. Experimenters also estimated the probability of the process (4.8 ± 0.5(stat.) ± 1.2(syst.)) × 10-4. Source: http://arxiv.org/abs/0807.1086 “Classical” atom1 August 2008Â. Dunning (Rice University, USA) and his colleagues prepared a potassium atom in which an electron was localized with high accuracy and revolved around the nucleus as a pointlike particle on an almost perfect circular orbit. Laser light transferred the atom to a highly excited Rydberg state. Then a special sequence of short electric pulses localized the electron. Localization survived for several orbits of the electron around the nucleus. The size of the electron's orbit reached a record value — approximately 1 mm. Similar quasiclassical systems were studied earlier (see Physics Uspekhi 47 531 (2004)) but the new experiment produced the highest degree of resemblance of the potassium atom and N. Bohr's planetary model of the atom. Source: Phys. Rev. Lett. 100 361 (2008) Structure of liquid water1 August 2008The crystal structure of water ice is tetrahedral. It was normally assumed that as ice melts, the long-range crystal ordering is destroyed but that on a small scale water molecules mostly stay near the nodes of the tetrahedral lattice. A. Nilsson and his colleagues at Stanford Synchrotron Radiation Laboratory conducted a new experiment to study the arrangement of water molecules in liquid water. A powerful x-ray beam from the synchrotron light source excited oxygen atoms and the pattern of ordering of water molecules was studied by recording their radiation by x-ray emission spectroscopy techniques. It was found that tetrahedral structure can indeed be traced in the arrangement of molecules but that a different, less pronounced type of ordering dominates in a substantial part of the volume. Each type of ordering corresponded to an individual maximum in the radiation spectrum. The first to advance the hypothesis that water possesses two types of ordering in an attempt to explain the unique properties of water was Willhelm Conrad Röntgen. The results obtained at SLAC may prove important for microbiology and other fields of science and technology. Source: Chemical Physics Letters 460 387 (2008) Relativistic precession in double pulsar1 August 2008R.P. Breton and his colleagues carried out a detailed study of the double pulsar PSR J0737-3039A/B. Very small tilt of the plane of orbit relative to our line of sight permits observation of eclipsing signal from pulsar A: the signal is absorbed by the magnetosphere of pulsar B. Assuming a simple geometrical model of the magnetosphere it was possible to measure the rate of relativistic precession of the axis of revolution of pulsar B relative to the direction of the net angular momentum of the binary system. The obtained estimate corresponds to the predictions of General Relativity Theory; furthermore, this test refers to the range of strong gravitational fields. Relativistic precession in a strong field was measured for the first time for a double pulsar PSR B1534+12 but the accuracy was lower than that achieved for PSR J0737-3039A/B. Sources: Science 460 321 (2008), http://arxiv.org/abs/0807.2644 Gamma emission from a remote quasar1 August 2008The ground-based gamma telescope MAGIC recorded Vavilov – Cherenkov radiation from cascades of charge particles created in the interaction between cosmic gamma photons and atoms in the atmosphere. MAGIC recorded a gamma burst from a remote gamma source at a record distance: the 3C 279 quasar at a distance of nearly 5 billion light years from Earth (its red shift is z ≈ 0.536). The source of this emission is most likely the accreting black hole in the quasar core. Gamma photons are capable of interacting with the intergalactic background radiation; consequently, the fact itself of detecting photons with energies above 50 GeV indicates that for 5 × 109 years the density of background radiation in certain ranges of the spectrum was below a threshold value at which the observed gamma radiation would be absorbed. In their turn, background restrictions impose limitations on the characteristics of evolution of galaxies and stars that produce the background. The observation of gamma emission from 3C 279 is an evidence supporting the models of evolution with low background density. In contrast to microwave background, low density and strong interference from nearby sources in the Galaxy make it difficult to measure directly the level of intergalactic background. Source: Science 320 1752 (2008) |
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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