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| Issue 11, 2024 |
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Extracts from the Internet | ||
Neutrino oscillations1 July 2010A number of experiments studying neutrino oscillations observed a reduction in the number of muon neutrinos along neutrino beams; this, however, was only an indirect indication that a different species of the neutrino appeared in the beam. A qualitatively new result is now reported at the experiment OPERA where the first appearance of tau neutrinos in the beam of muon neutrinos was recorded. The OPERA detector at the Gran Sasso National Laboratory (Italy) sits in a tunnel under a massive mountain. The working substances of the detector are emulsion films alternating with plates of low-background-noise lead. In 2008 and 2009 the facility monitored the νμ beam with energy of about 17 GeV, sent into the OPERA detector from the accelerator at CERN at a distance of 730 km through the body of the Earth. The candidate event involving ντ was identified by the characteristic topology of the decay of the τ-lepton which was created in the interaction between the ντ and a lead nucleus. The detection of the first candidate event of ντ with certainty of 98% points to appreciable effect of neutrino oscillations νμ → ντ. The confidence in the reality of neutrino oscillations will be achieved only after several such events will have been recorded. Neutrino oscillations assume that neutrinos have mass, which means going beyond the tenets of the Standard Model of elementary particles. The OPERA experiment it being conducted by the international team of researchers from 12 countries, which includes researchers from five research institutions in Russia. In another experiment, MINOS (being run since 2005 at the E. Fermi National Laboratory), a very accurate comparison of the effects of neutrino and antineutrino oscillations has been realized. The MINOS detector is located at a distance of 735 km from the accelerator which generates the νμ and anti-νμ beam. The process occurring in the detector is the magnetic separation and recording of muons and antimuons generated by the interaction of νμ and anti-νμ with the material of the detector. An unexpected result was obtained: the squared mass difference of neutrinos, Δ m2, is 40% smaller than for the corresponding species of antineutrinos. However, the statistical significance of this result is only about 2 σ which means that further testing is necessary. New theoretical approaches will have to be worked out in order to explain this fundamental difference between the neutrino and the antineutrino, provideded its reality is confirmed. Sources: arXiv:1006.1623v1 [hep-ex], physorg.com Quantum teleportation to a distance of 16 km1 July 2010Õ.-Ì. Jin and his coworkers in China performed an experiment on quantum teleportation of photon states through air at a distance of 16 km. In the past it was only possible to implement teleportation over a distance of several tens of meters for photons transmitted through an optical fiber. Quantum teleportation assumes that a change in the state of one particle of a pair instantaneously changes the state of the second remote particle which is in entangled quantum state with the partner particle, i.e. the quantum state has been teleported. Quantum entanglement of the state of motion of one photon and the state of polarization of the second photon was produced here in a nonlinear crystal, after which one of the photons of the pair was sent into the detector located at a distance of 16 km. The two photons remained entangled with fidelity of 89%, which is considerably higher than the classical limit equal to 2/3. The experiment implemented all the main components of the scheme of quantum teleportation, with the exception of the local unitary operation. Successful quantum teleportation at the Earth's surface over a distance of 16 km (exceeding the effective thickness of the atmosphere (≈10 km) has demonstrated the possibility of using this effect in optical communication channels between ground stations and satellites. Source: Nature Photonics 4 376 (2010) Organic compound with metal's properties1 July 2010Researchers from the RAS Institute of Problems of Chemical Physics and Institute of Solid State Physics together with their colleagues in Japan succeeded in synthesizing N-methyl-ethyldiazobicyclooctane-triptycene-C60 an organic material which contains no metal atoms but possesses metallic properties. The new crystalline material was obtained by diffusion method and its structure was studied by X-ray diffraction. The material consists of planar layers in which C60 anions are arranged in honeycomb pattern, fullerene layers alternating with layers of molecules containing only atoms of light elements: hydrogen, carbon and nitrogen. The dense packing structure in the arrangement of fullerene molecules is supported by ring molecules of aromatic hydrocarbon triptycene C20H14. Direct measurements using electrical contacts fixed to specimens show that at temperatures above 1.9 K electric conductivity of the material is at the level of metallic conductivity. Source: Angewandte Chemie 49 4829 (2010) Instantaneous velocity of a Brownian particle1 July 2010Ò. Li (University of Texas at Austin, USA) and colleagues studied the Brownian motion of silica beads SiO2 about 3µm in size in air and for the first time measured their instantaneous velocity. Typically experiments follow the diffusive mode of Brownian motion over relatively long stretches of time when ⟨(Δ x)2⟩ ∝ t. However, over very short intervals of time shorter than the relaxation time of particle momentum, the particle moves by inertia, in ballistic mode. A particle of SiO2 was trapped into an optical tweezer formed by two focused laser beams. The motion of a particle, which is described by the Langevin equation in harmonic potential, was observed in the reflected laser light at high time resolution. As expected, over short time intervals the relation is ⟨(Δ x)2⟩ ∝ t2. Furthermore, it has been established that the distribution of Brownian particles corresponds to the Maxwell – Boltzmann distribution and that the particle energy conforms with the energy equipartition theorem. Source: Science 328 1673 (2010) Anisotropy of cosmic rays in Southern hemisphere1 July 2010A number of experiments conducted in the Northern hemisphere detected a slight anisotropy (of about 10-4 – 10-3) in the distribution of cosmic rays with energies up to several TeV. Similar measurements of anisotropy in the TeV region in the Southern hemisphere were first carried out in the IceCube experiment conducted in Antarctica at the South Pole. The main purpose of the IceCub experiment was to record neutrino events but it can also measure the flux of cosmic rays. IceCube is to reach effective volume of 1 km3 and total functionality in 2011 by which time 5160 optical modules are expected to be installed on 86 strings in the ice at depths from 1450 to 2450 m. The described measurements were conducted in 2007-2008 with only 22 strings installed. Among the recorded data, 4.3 × 109 reliable events of detecting cosmic rays particles with energies up to 20 TeV were selected, and the directions were measured with angular resolution of 3°. Careful work was carried out for removing from the experimental data the effects of asymmetric geometry of the detector, seasonal variations and other factors that could distort the result. The distribution of the measured intensity of cosmic rays in the Southern sky smoothly matches the distribution which was previously obtained in the Northern hemisphere. One possible explanation of the anisotropy lies in the peculiarities in the distribution of interstellar magnetic fields in the vicinity of the Sun on a scale less than one parsec. The nature of this anisotropy will probably be clarified after the planned IceCube measurements of anisotropy as a function of energy of particles. Source: arXiv:1005.2960v1 [astro-ph.HE] |
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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