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| Issue 12, 2024 |
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Extracts from the Internet | ||
u- and b-quark coupling strength1 September 2015In the LHCb experiment carried out on the Large Hadron Collider, the u- and b-quark coupling strength characterized by the element Vub of Cabibbo–Kobayashi–Maskawa (CKM) matrix was first measured by studying the baryon decay. |Vub| was measured earlier in B-meson decay reactions only, the exclusive and inclusive determinations showing discrepancy at the level of 3 σ. In the LHCb experiment, the Λb0-baryon decay probability was measured and |Vub| was found, the Λb0 → pμ-(anti)νμ decay channel being examined for the first time. The value |Vub| agrees well with the results of previous exclusive measurements in B-meson decays, but does not confirm inclusive measurements at the level of 3.5 σ. Although the Standard Model does not predict the value of the CKM matrix elements, it requires consistency in different processes. For this reason, to explain the discrepancy between |Vub| measurements effects beyond the Standard Model were involved, for instance the supersymmetry theory. To find or restrict the possible contribution of the new effects the inclusive measurements should be additionally verified. Source: Nature Physics, online publication of July 27, 2015 Observation of neutrino oscillations in NOvA experiment1 September 2015The new NOvA experiment studying neutrino oscillations yielded first results. The muon neutrino beam from the Fermilab accelerator is first observed in the near neutrino detector measuring the primary beam composition and then passes 810 km in the depth of the Earth to the 14-kiloton far detector. Oscillations are registered both by the method of νμ “disappearance” from the beam and the method of νe “appearance”. In the absence of oscillations the far detector would register 201 νμ, whereas it actually registered 33. And at the same time six νe were detected, while the calculated number of background events was only 1. Owing to the record beam power of 521 kW with a planned increase up to 700 kW the NOvA experiment opens rich prospects, and with gathering statistics valuable information can be obtained on the parameters of neutrino oscillations, including mass hierarchy. Russian researchers from the INR RAS, LPI RAS, and JINR took part in the NOvA experiment. Source: Fermilab Press Release Verification of the uncertainty principle in terms of the information theory1 September 2015G. Sulyok (Vienna University of Technology, Austria) with colleagues fulfilled an experimental verification of the quantum-mechanical uncertainty principle reformulated in terms of the information theory, i.e., through the values of information received and lost in measurements. In such a form the uncertainty principle was formulated by F. Buscemi et al. In G. Sulyok’s experiment the quantum variables are represented by neutron spins. A neutron beam was generated in the research atomic reactor in the Vienna University of Technology, and neutrons were detected after spin rotation in the magnetic field. Measurements confirmed the informational formulation of the uncertainty principle, and in the presence of optimal correction the regime of saturation set in when inequality passes over to equality. Source: Phys. Rev. Lett. 115 030401 (2015) Observation of quasi-particles — Weyl fermions1 September 2015Three independent teams of research workers discovered quasi-particles possessing the properties of Weyl fermions, i.e., behaving as massless solutions of the Dirac equation. Su-Yang Xu (Princeton University, USA) with colleagues observed Weyl fermions in the semimetallic compound TaAs by the method of photoemission spectroscopy. These fermions were detected by the presence near the crystal surface of characteristic “Fermi arcs” that end at the projections onto the crystal surface of Weyl nodes observed in the sample depth. A similar method of TaAs examination was also applied by B.Q. Lv (Beijing National Laboratory for Condensed Matter Physics, China) et al. However, the third team, L. Lu (Massachusetts Institute of Technology, USA) et al. observed Weyl fermions in another system, namely, in photon crystals having the structure of double rotoinversion axes. Transmission of microwave radiation with different frequencies and at different angles through crystals was investigated and “Weyl points”, that is, dispersion curve intersection points were revealed. Weyl fermions moving at high velocities and possessing topological stability under scattering can find application in nanoelectronics. Sources: Science 349 613 (2015), Science 349 622 (2015), arXiv:1502.04684 [cond-mat.mtrl-sci] Directional radiation of quantum dots1 September 2015P. Lodahl and his colleagues from Niels Bohr Institute (University of Copenhagen, Denmark) displayed the possibility of photon emission by quantum dots in one prescribed direction. A quantum dot was engineered by the method of electron-beam lithography and its radiation was laser-generated. Photons with given circular polarization were emitted through the action of the magnetic field on the spin state of the electrons. Moreover, the dot was transversed by a photon channel with anisotropic (owing to chiral interaction) optical properties. For this reason the quantum dot worked in phase with only the electromagnetic mode corresponding to one of the channel arms, and photons were emitted predominantly in either of the two possible directions. Source: Nature Nanotechnology, online publication of July 27, 2015 Formation of a central compact object in a binary system1 September 2015Compact X-ray sources are observed in centers of several young supernova remnants. These are assumed to be isolated neutron stars born in explosions. Researchers from the University of Tubingen (Germany) and Kazan’ Federal University (Russia) were the first to obtain evidence that in one of such remnants (G353.6-0.7) a neutron star could have originated in a binary system. A star that has passed the stage of asymptotical giant branch is observed in G353.6-0.7 at a distance of 0.4 pc from the compact source. V. Doroshenko with colleagues compared the IR observations of Spitzer space telescope with the X-ray images to arrive at the conclusion that the star that underwent explosion and the observed star had constituted a binary system which exploded and decayed 4 to 10 thousand years ago, although now its components fly away from each other and are not connected gravitationally. Furthermore, the IR radiation of a massive dust shell around the star was found to be partially generated by X-ray emission of the neutron star. Source: arXiv:1508.03557 [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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