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| Issue 11, 2024 |
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Extracts from the Internet | ||
The asymmetry in t-anti-t pairs1 February 2011The CDF Collaboration of the Tevatron accelerator of the E. Fermi National Laboratory measured the spatial asymmetry of the forward-backward production of quark-antiquark t-anti-t pairs in ð-anti-ð collisions. This asymmetry arises because the positive charge of the proton repels the t-quark and attracts the anti-t quark, so as a result the t-quark and the jets of particles it produces are ejected with higher probability in the direction of motion of the ð. So far 1260 events have been analyzed in which at least one of the t or anti-t-quarks has undergone a semilepton decay of the type t → lνb while the second quark decayed through the hadron channel t → qq'b. In the rest frame of the t-anti-t pair the asymmetry depends on pseudorapidity η and invariant mass M. For M > 450 GeV/c2 the measured asymmetry was 48 ± 11 % while taking into account the first correction in the Standard model gives 8 ± 1 %, i.e. the statistical significance of the difference is 3,4σ and asymmetry agrees with the predicted value at smaller M. These measurements are important for testing predictions and searching for new effects, such as exotic heavy resonances which, according to some hypotheses, may contribute to asymmetry. Source: arXiv:1101.0034v1 [hep-ex] Trions in carbon nanotubes1 February 2011Researchers at Kyoto University (Japan) R. Matsunaga, Ê. Matsuda è Y. Kanemitsu for the first time produced and observed trion quasiparticles in carbon nanotubes. Trions (also known as charged excitons) are three-particle bound states consisting of one electron and two holes (electron vacancies). Trions have been observed at room temperature by optically excitating p-doped nanotubes and recording their absorption spectra and photoluminescence. The energy of the spectral peak corresponding to trions is lower than that of bright excitons by 0.1-0.2 eV. The considerable difference between peak energies may be caused by strong electron-hole interaction in carbon nanotubes. Trion have been observed earlier in a number of different systems. The distinguishing feature of trions is that they carry a charge and therefore can be controlled by electric fields; consequently, this property may in the future make them useful for nanotube-based spintronic devices. Source: Phys. Rev. Lett. 106 037404 (2011) The symmetry of the Möbius strip in metamaterials1 February 2011A group of researchers at the University of California led by X. Zhang developed a metamaterial whose electromagnetic properties manifest a topological C3 symmetry of the Möbius strip which has no analogs in natural materials. The metamaterial was obtained using standard electron beam lithography techniques. It constitutes a mass of metaatoms forming trimers of composed of metallic segments. The number of “Möbius twists” corresponds to the number of sign changes in the interaction between a metaatom and its neighbors under 360° rotation, which is a result of segment configuration. The spectrum of radiation transmitted through the metamaterial was studied using infrared spectrometry. The topological nature of the obtained resonances (i.e. dips in the spectrum) is confirmed by the fact that the resonances predominantly depend on the number of “twists” and are less sensitive to other characteristics of metaatoms. Source: Phys. Rev. Lett. 105 235501 (2010) Friction on a superconductor1 February 2011Ì. Kisiel and his colleagues studied the contribution of electron and phonon excitations to the effect of contactless friction between a micromechanical probe (cantilever) and superconducting film at temperatures close to Tc. Ì. Kisiel et al studied the effect of friction on cantilever vibrations in vacuum at a distance of ≈ 0,5 nm from the niobium film. As the film cooled below Tc the friction coefficient decreased by a factor of about three. This is an indication that electron friction dominates in the metallic state and that phonon friction begins to dominate after the transition to superconducting state, because electrons form Cooper pairs and thus cease to take part in friction. The relation between friction coefficient and distance to the film and between friction coefficient and the potential difference between specimens as observed in the experiment are in good agreement with the theoretical curve. Source: Nature Materials 10 119 (2011) The results of the Plank telescope observations1 February 2011Observational data is presented, obtained by the Planck space telescope since mid-2009. The telescope was placed at the Lagrange point L2 at a distance of 1.5 million km from the Earth. It is an array of 74 detectors operating at frequencies from 25 to 1000 GHz, i.e. at the boundary between the IR and radio bands. The spectrum of perturbations of the microwave radiation was measured in the IR band for multipoles l=200-2000. The statistical characteristics of anisotropy are identical at frequencies from at least 217 to 857 GHz. A catalog of compact and unresolved objects was also compiled; it includes thousands of relatively cold individual sources. The population of remote galaxies was analyzed, in which intense star formation is proceeding at a rate exceeding the current star formation rate in our Galaxy by a factor of 100 to 1000. The observation of these galaxies in other bands meets with difficulties because their emission is absorbed by dust clouds. In order to record the microwave background and individual objects it is of paramount importance to carefully filter out the diffuse background radiation emitted in the Galaxy in collisions of atoms and photons with interstellar dust; consequently, this dust also became one of the main objects of study. By the data of the Planck telescope, dust particles in gas-dust clouds rapidly revolve due to collisions with atoms of gases and UV photons; their rotation generates anomalous microwave radiation in the range ≈ 10-60 GHz. Cold gas-dust blobs in the Galaxy at temperature 7-17 Ê and mass (1-105)M☉ were studied. These clusters are distributed in the shape of filaments associated with molecular clouds; with time, new stars will start forming in many of them. Considerable success was acieved in studying galaxy formation by following the Syunyaev – Zeldovich effect. The Syunyaev – Zeldovich signal was measured for 169 clusters, of which 20 were identified for the first time. Power formula dependence was confirmed for the Syunyaev – Zeldovich effect as a function of richness (the number of galaxies) of clusters. The Planck data were compared with the observation of clusters in the x-ray band on the XMM-Newton X-ray observatory and good agreement was found with predictions based on dynamic models of clusters. The Planck and XMM-Newton telescopes discovered a supecluster of galaxies at redshift z = 0,45 — a rather unexpected result. Sources: arXiv:1101.2022v1 [astro-ph.IM], www.esa.int |
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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