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Issue 12, 2024
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Extracts from the Internet


Violation of CP invariance

The Belle collaboration at the Japanese KEK laboratory has obtained data contradicting the Standard Model of elementary particles. Two years ago experiments by Belle and those by BaBar (Stanford) discovered the violation of CP invariance in a system of B mesons. The major parameter characterising the CP violation, sin2phi1, turned out to be 0.731+-0.056, in good agreement with data of many other experiments. According to the Standard Model, this parameter should have the same value for all processes possible. Now the Belle collaboration conducted a new experiment, in which the decay mode involving the phi- and Ks-mesons, i. e., B0->phi+Ks, was studied. It turned out unexpectedly that the value of sin2phi1 for this reaction is -0.96+-0.50, with expected statistical fluctuation of less than 0.1%. The reaction B0->phi+Ks passes through a quantum fluctuation in which a b quark inside a B meson is split into a t quark and a W boson for a short period of time. A possible explanation for the observed anomaly is that in some cases a new, not yet discovered particle appears instead of the t quark and W boson - one of those predicted by the supersymmetric models, for example. To verify the Belle results, independent experiments are needed. Source: http://www.kek.jp/press/2003/belle3e.html

Bose-Einstein condensate of ytterbium atoms

Y Takahashi and colleagues at Kyoto University in Japan have for the first time created a Bose-Einstein condensate of ytterbium atoms, atoms which have two valence electrons. The atoms of the condensate were in a singlet nonmagnetic state, in which the electron spins are oppositely directed. The Bose-Einstein condensates of other elements obtained thus far have been in the `magnetic state': either their atoms had one valence electron, making the material paramagnetic; or (in the case of helium) two valence electrons were in the triplet state with their spins aligned. The researchers used an optical method to obtain ytterbium condensate. To trap the atoms and to evaporatively cool them, laser beams were employed. About 5000 ytterbium atoms were condensed and stayed in this state for about half a second in the Kyoto experiment. The Bose-Einstein condensate of ytterbium can be used in atomic clocks and in experimental tests of fundamental symmetries, the authors of the experiment believe. The study of degenerate gases consisting of other stable isotopes of ytterbium is also of interest. Source: Phys. Rev. Lett. 91 040404 (2003)

A quantum logic gate using excitons

D Steel and his colleagues from the University of Michigan have created a quantum logic gate using two excitons enclosed in a quantum dot. The term exciton refers to a system of an electron and an electron vacancy, a hole. The semiconductor `quantum dot' was a layer of gallium arsenide sandwiched between two barriers made from a compound of aluminium and gallium arsenide. Because the energy gap of gallium arsenide was narrower than that of the barriers, the electrons turned out to be trapped in the quantum dot. There were four states in the system: one state with two non-excited electrons, two one-exciton states of different polarization, and a two-exciton state. To excite electrons and control the logic state of the gate, light pulses were used. The cell worked with two qubits of information and could act as a logical `NOT' operation. Source: Science 301 809 (2003)

The cosmological constant

R Scranton and his colleagues of the University of Pittsburgh in the US have found new independent evidence for the existence of vacuum energy (cosmological constant) in the Universe. They discovered achromatic positive correlations between the microwave background radiation fluctuations measured in the WMAP experiment and the galaxy distribution revealed by the Sloan Digital Sky Survey. The correlations are consistent with those expected due to the integrated Sachs-Wolfe effect and are due to background radiation photons flying through low matter-density (high galaxy concentration) regions of space. Because of the equation state p=-e, the vacuum energy acts to decrease the depth of gravitational potential wells. It is the influence of this effect on the form of the correlations which enabled the presence of the cosmological constant to be revealed. Source: http://arXiv.org/abs/astro-ph/0307335

Non-spherical supernova explosion

Astronomers from Berkeley National Laboratory, the European Southern Observatory (ESO), and the University of Texas has for the first time discovered non-sphericity in a type Ia supernova explosion. Using the VLA telescope located in Chile, the supernova 2001el was monitored in the Galaxy NGC 1448. At the peak of the supernova's brightness, it was found that the radiation from the supernova was polarized, indicating that the expanding shell of the supernova is non-spherical in shape. The shell's minor axis size was 10% smaller than that along the major axis. A week later the polarization disappeared. This is likely due to the inner, more spherical layers having come to dominate the brightness. The study is important for cosmological measurements because type-Ia supernovas are used as `standard candles' at cosmological distances. In particular, it is from the observations of these supernovas that the presence of the cosmological constant in the Universe was first concluded. Source: http://arxiv.org/abs/astro-ph/0303397; http://www.lbl.gov/Science-Articles/Archive/Phys-supernovae-shape-up.html

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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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