RSS feeds
ÐóññêèéEnglish
Issue 11, 2024
Volume year page
Issues Authors PACS Subscription For authors

Extracts from the Internet


Anomalous ÑÐ-violation

The D0 collaboration at the Tevatron accelerator in the Enrico Fermi Laboratory detected asymmetry of semilepton decays of B0q and anti-B0q-mesons (q = d, s) which may point to new physics beyond the boundaries of the Standard Model of elementary particles. Pairs of B0q and anti-B0q-mesons were created in p-anti-p- collisions. Among the products of decay of B0q and anti-B0q were antimuons μ+ and muons μ-, respectively. The particles B0q and anti-B0q may transform into one another (oscillate) in processes involving two bosons W±. The emergence of lepton pairs with identical sign of charge, μ-μ- or μ+μ+, among decay products was an indication that such an oscillation has taken place, and the excess of the number of μ+μ+ over that of μ-μ- detected in the D0 experiment pointed to asymmetry in the direction of oscillations. The asymmetry due to violation of CP invariance is indeed predicted by the Standard model but the measured value of asymmetry was found to be greater than the precicted one, the difference being 3.2 standard deviations. The additional ÑÐ violation above the Standard Model level has been expected by theorists for some time now as it is required for explaining the dominance of matter over antimatter in the Universe. Source: Phys. Rev . Lett. 105 081801 (2010)

Three-slit quantum interference

G. Weihs (Innsbruck and Waterloo Universities) and his colleagues from Canada, France and Austria performed an experiment which studied the interference of photons sent through three slots. Unlike the case of two slits, fundamental predictions of quantum mechanics for three-slit interference have not been tested in the past. In terms of the standard approach the probability density of a photon at a given point on the screen behind slits is given by the quadratic formula (Born rule) PABC = | ψA + ψB + ψC |2 in terms of the probabilities of two-slit (PAB = | ψA + ψB |2 etc) and one-slit (PA = | ψA |2 etc) measurements. Deviations from this expression, such as higher-order terms, could be expected in generalizations of quantum mechanics. The researchers studied the transmission of single photons emitted by the source of very low luminosity through three slits 30µm wide each, separated by gaps of 100µm each. A series of measurements have been performed for all possible combinations with one and two closed slits and with three open slits. The above expression for PABC containing probabilities of one- and two-slit measurements has been confirmed at the acheved experimentsl accuracy of 1%, i.e. no deviations from the Born rule have been found at this accuracy. Source: Science 329 418 (2010)

Turbulence in superfluid helium-4

Heat from heating source is transferred in superfluid liquids by a reverse flow of the normal component of the liquid (in terms of the two-liquids model). A number of experiments demonstrated that the flow of the superfluid component becomes turbulent at a sufficiently high heating power and that the movement of quantized vortex filaments is also tubulent. Similar studies on the normal component have not been carried out in view of the absence of suitable markers that would allow monitoring its speed. W. Guo (Yale University) and his colleagues from the U.S. and UK have established using the new technique that the flow of the normal component of 4He in a glass tube also changes to the turbulent mode when the liquid at one of the ends of the tube is heated at a sufficiently high power level. Metastable He2 molecules in triplet state were formed in the tube by the electric field and their fluorescent light emission was observed after excitation by laser pulses. He2 molecules moved together with the normal component of the liquid; owing to their small size they were not captured into vortex filaments and were practically unscattered by them, unlike what took place in experiments with macroscopic markers. Lines of molecules oriented transversely to heat flow remained straight at sufficiently high heating power and grew broader. This pointed to a flat velocity profile in the tube and the presence of additional disordered molecular velocities; this is typical of turbulent flow. The parabolic profile of velocities at low levels of heating was revealed by studying compact clusters of molecules at various distances from the flow axis. In this last case both the superfluid and the normal components of the liquid were in a laminar mode of flow. Source: Phys. Rev . Lett. 105 045301 (2010)

Active metamaterial

Metamaterials with a refractive index n < 0 that were first investigated theoretically by V.G. Veselago (see Sov. Phys. Usp. 10 509 (1968)), may in the future find numerous useful technical applications. At the moment their utilization is thwarted by high dissipation of electromagnetic waves by metallic components of the metamaterial. V.M. Shalaev and his colleagues in the USA designed a metamaterial incorporating in its structure molecules of a fluorescent dye Rh800. Rh800 molecules are excited by laser pulses (pumping pulses) so that the second light pulse can for some time stimulate light emission in reverse transitions to ground state. The optimum time between pumping pulse and probe pulse was 54 ps. As a result the metamaterial acquired the properties of an optical amplifier at wavelengths of 722-738 nm and it compensated for the losses in the reflected and transmitted signals, plus it increased the magnitude of the negative refractive index. This method of creating active metamaterials was discussed some time ago in a number of theoretical papers but practical implementation in the near future was considered very problematic. Source: Nature 466 735 (2010)

Star — a predecessor of magnetar

As a rule, a stellar cluster is formed after an individual cloud of gas has fragmented. As a result, all starts of the cluster are of nearly the same age. The rate of evolution of individual stars in a cluster is dictated most of all by their masses — the more massive a star, the faster its evolution, and if the mass is sufficiently large, the star would explode as a supernova. The open cluster of young stars Westerlund 1 is observed in the Ara constellation, and the same cluster contains a magnetar CXOU J164710.2-455216 — a neutron star possessing giant magnetic field. Theoretical models and the data of indirect observation indicate that magnetars are born in explosions of very massive stars. This conclusion received additional support in new observations on the VLT telescope of the European Southern Observatory (ESO) in Chile. To determine the lower limit of stellar mass whose explosion gave rise to the magnetar, the masses were determined of two other stars in the same cluster forming a binary system W 13. The characteristics of their orbital motion and photometric data established that the masses of these stars are close to 23 and 35 solar masses. A star — the predecessor of the magnetar — cannot have a smaller mass because it was born simultaneously with the stars of the pair W 13 but had exploded before them. Taking into account the mass loss by the stars of the binary system W 13 during its evolution, it was concluded that the mass of the predecessor star of the magnetar CXOU J164710.2-455216 was 40 to 45 times greater than the solar mass. Source: www.eso.org

News feed

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.
© 1918–2024 Uspekhi Fizicheskikh Nauk
Email: ufn@ufn.ru Editorial office contacts About the journal Terms and conditions