1 June 2005
New data on the formation of quark-gluon plasma in collisions between ultrarelativistic gold ions have been obtained at the RHIC heavy ions accelerator at Brookhaven National Laboratory. The center-of-mass energy of the collisions was 40TeV. Based on the characteristics of the particles flying away from the collision point, a physical picture of what is happening in these collisions was reconstructed. The decays of the nuclei first into nucleons and then into quarks give rise to a fireball consisting of mixture of quarks and gluons, a state of matter that existed early in the evolution of the Universe, only microseconds after its birth. Within about 10-24s the ball expands to a radius of 5fm, and the resulting cooling of the plasma causes the quarks to combine to form detector-registered hadrons. The experiments have provided solid evidence for claiming that the state created in collisions is indeed that of quark-gluon plasma. The key difference from previous experiments is that the quark-gluon plasma here behaves as an ideal liquid rather than as a gas - possibly because quarks and gluons interact rather strongly between themselves.
A hybrid meson
1 June 2005
A 3940-MeV mass meson consisting of a c-quark and a c-antiquark has been discovered by the Belle collaboration at the KEK Laboratory in Japan. The new mesons were created in electron-positron collisions and identified by their decay into Omega and J/psi particles. Some of the characteristic features of the decay suggest that the new meson is not merely a c anti-c pair but rather also contains a gluon - making it the first discovery of the `hybrid meson' predicted back in 1978. The mass of the new meson, however, is much smaller than theoretically predicted.
Source: Phys. Rev. Lett. 94 182002 (2005)
1 June 2005
An international team of researchers at the Ganil laboratory in France has for the first time succeeded in creating nuclei of the zinc isotope 54Zn , containing 30 protons and 24 neutrons. The 54Zn nuclei were produced by colliding a 58Ni beam with a nickel target and established to undergo the two-photon decay, with exactly the predicted values of the emitted proton energy and the decay half life of the nucleus. Since its prediction by V.I.Gol'dansky in 1960, the only material to experimentally exhibit the two-photon decay has been the 45Fe isotope
(see Phys. Usp. 45 1107 (2002)).
1 June 2005
E.Gregoryanz and his colleagues at the Carnegie Institution of Washington have observed the melting behavior of sodium to be quite unusual at high pressures. As in most other materials, its melting point first increases with increasing pressure, reaching 100K at 30GPa, but further increase in pressure starts to lower it - even down to room temperature at a pressure of 118GPa. Scientists have observed such `negative melting curves' in several substances, but at much lower temperatures and pressures.
Source: Physics News Update, Number 730
Metamaterials in the optical range
1 June 2005
V.Shalaev and his colleagues from the US have for the first time created a material with a negative refractive index n=-0.3 in the optical range, at a wavelength of 1.5mkm. Metamaterials with both a negative electric permittivity and a negative magnetic permeability were theoretically investigated by V.G.Veselago in 1967 (Sov. Phys. Usp. 10 509 (1968)), but so far this property has only been implemented (in composite materials) for the radio range (Phys. Usp. 43 520 (2000)). The new material consists of an array of microscopic nanoscale pairs of parallel gold wires, and the sample studied was 2mm by 2mm in size. The refractive index was experimentally measured by the amount by which the phase and amplitude of the transmitted and reflected waves changed. The negative n effect observed is due to plasmon resonances in the wires, which can be visualized as occurring in LC circuits with the wires and the dielectric-filled space acting as inductors and capacitors, respectively. The new metamaterials appear to be promising for practical applications. Source:
Taking a different approach, a University of California team led by X.Zhang has shown that a very thin (35nm) silver film may have a negative refractive index. This property, due to plasmon excitations occurring in the film, can be used to detect electromagnetic waves near the surface of objects. Surface waves, unlike ordinary light, decay exponentially with distance. By placing the object and the photoplate very close to the film, it proved possible, using an UV laser, to produce images with a resolution of one sixth the wavelength - which means beating the diffraction limit. The idea of using metamaterial lenses to detect surface waves was suggested by J.Pendry in 2000.
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.