Parameters of the unitarity triangle
1 May 2005
The most accurate measurement yet of the angle in the unitarity triangle, a graphical representation of the Cabbibbo - Kobayashi - Maskawa matrix, has been carried out by the Belle collaboration at the KEK laboratory in Japan. The role of the CKM matrix in the Standard Model of elementary particles is one of describing CP violation and the particle-antiparticle difference. In the course of the experiment the Belle team obtained 275x106-meson pairs and studied their decay into neutral D-mesons and charged kaons, which in 56 observed events was followed by a D-meson decay into a pion pair and a kaon. From the difference in the decay characteristics between B-mesons and anti-B-mesons, the team calculated that the angle of unitarity triangle. The data processing techniques used in the experiment was the Dalitz plot analysis. Measuring the unitarity triangle parameters is important in the search for new effects as well as a tool for checking the Standard Model for selfconsistency. Participating in the international experiment were Russian scientists from the G I Budker Institute of Nuclear Physics (Novosibirsk) and the Institute of Theoretical and Experimental Physics (Moscow).
The halflife time of 78Ni
1 May 2005
A team of German and American researchers have for the first time measured the halflife of 78Ni. This nucleus is `doubly magic' (i. e., has all its nucleon shells closed) and is crucially important for the formation of heavy elements in the Universe: the rapid capture of neutrons by 78Ni nuclei (the so-called r-process occurring in supernova explosions) produces more than half of all chemical elements beyond iron. Although 78Ni nuclei have been synthesized previously at the GSI Laboratory in Darmstadt, Germany, their halflife time proved impossible to measure. In the new experiment, conducted at the University of Michigan, the German-American team collided a beam of krypton with a beryllium target and measured the halflife time of 78Ni nuclei separated from the reaction products. The result, 110(+100 -60)ms, is four times shorter than the theoretical prediction. The experimental data are best fitted with the nuclear shell model and suggest that models of element synthesis in supernova explosions should be revised. The same experiment yielded the halflife times of the 75Ni,
76 and Ni77Ni. nuclei.
Source: Phys. Rev. Lett. 94 112501 (2005)
Measuring extremely small masses
1 May 2005
In a technique developed by M Roukes and his colleagues from the California Institute of Technology, extremely small masses can be measured based on the amount by which a microscopic oscillator changes its resonant frequency as its mass is increased. The oscillator, a flattened balance beam made from silicon carbide, was loaded at both ends, put in a deep vacuum, and exposed to a beam of xenon atoms, part of which it absorbed on its surface. The oscillator was placed in a radio frequency cavity, whose electric vibrations were measured in the Caltech experiment. The frequency shift is discernible when 30 xenon atoms (i.e., 7x10-21g in mass) are absorbed by the oscillator. The new technique may be useful in biomedical research for detecting large organic molecules.
Source: Physics News Update, Number 725
Electromechanics at the nanoscale
1 May 2005
A Zettl and his American colleagues have developed an electromechanical device only a few tens of nanometers in size, which relies on the phenomenon of surface tension for its mechanical motions. The device, called a relaxation oscillator, consists of two liquid indium droplets placed on a carbon nanotube substrate. Applying an external electric field causes the indium molecules to leave the larger droplet for the smaller one - ultimately making the latter big enough to touch the former. After that the backflow of indium due to surface tension starts to occur - thus leading to oscillations. It is found that the oscillation frequency depends on the electric field strength and that during each oscillation (about 200 ps in duration) a mechanical work of 5 fJ is performed.
Source: Appl. Phys. Lett. 86 123119 (2005)
A new class of cosmic gamma-ray sources
1 May 2005
The HESS telescope in Namibia has discovered eight new point sources of hard gamma-ray emission near the center of the Galaxy. HESS is a set of four Cherenkov detectors, each 107m2 in area, which operate jointly in a stereoscopic mode, thus providing a resolution of better than 0.1o The emission observed has an energy of more than 100 GeV. Gamma photons or cosmic rays entering the atmosphere trigger a cascade of charged particles, resulting in a Cherenkov radiation which is detected by telescopes. The eight previously unknown gamma-ray sources are located in the plane of the Galaxy close to its center. While six of them were identified as either supernova explosions or neutron stars or neutron star nebulas based on their observations at other wavelengths, the two remaining sources do not coincide with known astrophysical objects and are not seen in other wavelengths - suggesting they may form a new population of gamma-ray sources. The hard gamma radiation is likely due to the interaction between high-energy accelerated charged particles, and the fact that no long-wavelength radiation comes along points to protons as the most likely to be accelerated. This is another point where these two sources differ from the known objects where electrons are mainly accelerated.
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.