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| Issue 12, 2024 |
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Extracts from the Internet | ||
The existence of the 4-quark particle Z(4430)- is confirmed1 May 2014The birth of particle Z(4430)- consisting of four quarks c-anti-cd-anti-u was first evidenced by Belle collaboration on KEK accelerator (Japan) in 2008. In LHCb experiment on Large Hadron Collider its existence was confirmed with 13.9σ confidence. 25176 ± 174 decays B0 → ψ'K+π-, ψ' → μ+μ- of B0-mesons born in pp-collisions were examined. The decay product distributions measured by the invariant mass were modeled with allowance for the known resonant states K*. The states K* alone turned out to be insufficient for data reproduction, and an additional component is needed corresponding to a short-lived particle-resonance Z(4430)- with mass of nearly 4430 MeV, a resonance width of ≈ 172 MeV, a negative unit charge and spin parity JP=1+. Also measured were the interferential properties in the resonance region and the loop in the Argand diagram. At the present time, several particles are already known which can consist of four quarks, but it is only in the case Z(4430)- that the LHCb experiment showed reliably that this particle does belong to particles-resonances. The nature of Z(4430)- particle has not yet been clarified in full for it can be either a tetraquark or a coupled two-meson system. Source: arXiv:1404.1903 [hep-ex] Verification of the equivalence principle using neutrino1 May 2014The observed effect of neutrino oscillations testifies to the fact that the flavor states of neutrinos are a superposition of the mass states but are not coincident with them. The question arises of whether the interaction of each of the mass states with the gravitational field has the same form as that of nonoscillating particles, i.e., whether the equivalence principle holds for mass states. A. Esmaili (G.V. Wataghin Institute of Physics, Brazil) with colleagues studied this problem on the basis of data on atmospheric high-energy (Eν=20 GeV-400 TeV) neutrinos registered in the IceCube experiment being carried out in the Antarctic ice. Violation of the equivalence principle would cause an additional phase shift between the states inducing oscillations. Although no such additional oscillations were revealed, restrictions were obtained on the products of the gravitational potential φ and the differences of parameters γi defined as factors in the gravitational interaction of mass states. If the equivalence principle is valid, then γi=1 is equal to unity for i=1,2,3. It was found that |φ(γ2-γ1)|<9,1 × 10-27 and |φ(γ3-γ1)|<6 × 10-27. These restrictions are respectively 4 and 1 order of magnitude more rigorous than those obtained from other experiments. Thus, at today’s level of precision the IceCube data confirm the equivalence principle for neutrino mass states. Source: arXiv:1404.3608 [hep-ph] Quantum entanglement of three photons1 May 2014C. Erven (University of Waterloo, Canada) with colleagues demonstrated the effect of quantum entanglement of three distant photons in the case when the events of measurement of their states are separated by a space-like interval and, therefore, could not exhibit causal link. In earlier experiments this condition was only met for two particles. Three photons in spin entangled states were obtained by the method of parametric down conversion and mixing. Two photons flew toward detectors at distances of 700 to 800 m, while the optical path of the third photon was localized near the source. The detectors responded at random instants of time determined by random-signal quantum generator located at a distance of 446 m from the source. The states of the three photons were measured within the time interval in which the photons were unable to exchange signals propagating with the velocity of light. Violation of Mermin’s inequalities, an analogue of the Bell inequalities, but for three particles, was investigated. These inequalities were violated at the level 9σ, which testified with high confidence to quantum entanglement of three photons. The results of experiment both serve for verification of the fundamental bases of quantum mechanics and can find practical application in quantum cryptography and quantum communications. Source: Nature Photonics 8 292 (2014) Berry’s phase in a semiconductor1 May 2014If conductivity of a substance has nontrivial topological properties, the electron wave functions may show an additional phase shift (may have Berry’s phase) upon almost periodic changes in the states of the system. The Berry’s phase was observed in experiments with quantum Hall effect and topological insulators. The new observation of Berry’s phase, this time in BiTeI semiconductor with properties described by a Hamiltonian with spin-orbital interaction in the Rashba form, were performed by H. Murakawa (RIKEN Center for Emergent Matter Science, Japan) with colleagues. The conductivity of thin BiTeI layers in a magnetic field was measured at a temperature of 1.8 K. Two groups of oscillations corresponding to two spin states were revealed. The Berry’s phase for the internal Fermi surface (for a low external magnetic field B) was observed by oscillations of the second derivative of conductivity -d2ρxx/dB2. And the Berry’s phase for the external Fermi surface (for high B) was revealed by Shubnikov-de Haas oscillations which were observed up to B=56 T. The systematic phase shift of oscillations measured in experiment agrees with the theoretical predictions of the presence of Berry’s phase in the BiTeI semiconductor. Source: Science 342 1490 (2014) RadioAstron examination of interstellar plasma1 May 201410-meter space radio telescope RadioAstron and two ground-based telescopes (Arecibo and Westerbork Synthesis Radio Telescope) were used to observe radio pulses of pulsar PSR B0950+08 at a wave of 92 cm in the regime of ground-space interferometer and to receive information on the line-of-sight distribution of interstellar plasma which scatters the signal and causes its scintillations. The space and ground-based telescopes combine into an interferometer with baseline of 220000 km, providing the record angular resolution at meter wavelengths. The expected signal characteristics were calculated by T.V. Smirnova and V.I. Shishov as far back as 2008 and the results were confirmed with good accuracy in these observations. The signal scintillations had the form of modulation at a level of ≈40% with frequencies much lower than the carrier frequency. Such modulation could be caused by plasma configuration at the line of sight in the form of two scattering layers and a “cosmic prism” — a rather sharp plasma distribution gradient declining the radio emission by angles of 1.1-4.4 angular milliseconds. The far scattering layer lies most likely at the external boundary of the Local bubble (the rarified gas region inside the galactic arm) at a distance of 26-170 pc, and the near layer (4.4-16.4) lies on the ionized surface of molecular cloud. The spectrum of turbulent density fluctuations in both cases follows the power law with exponents γ1=γ2=3.00 ± 0.08, which differs from the Kolmogorov’s spectrum with γ=11/3. Most of these results could not be obtained by observations from the Earth surface only because under pulsar radiation refraction the Fresnel zone exceeds the Earth diameter. The RadioAstron was orbited in 2011 on board the space observatory Spectrum-P. This project is being implemented by the Astro Space Center of P.N. Lebedev Physics Institute and Lavochkin Research and Production Association with participation of other Russian and International Organizations. Source: Astrophysical Journal 786 115 (2014), arXiv:1402.6346 [astro-ph.GA] |
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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