 |
RSS feeds |
|
|||||
| Issue 11, 2024 |
|
||||||
|
|
|
||||||
Extracts from the Internet | ||
Velocity of neutrinos1 November 2011The OPERA experiment (Gran Sasso Laboratory, Italy) carried out direct measurements of velocity of muon neutrinos νμ in the beam that was obtained at the CERN accelerator and then traveled 730 km through the Earth. In 2009-2011 the OPERA detector registered 16111 neutrinos at energy of 17 GeV. To determine the distance between the source of νμ and the detector with an accuracy of 20 cm and for comparing atomic clocks at CERN and Gran Sasso with an accuracy of ≈ 1 ns, satellite-based GPS navigation signals were used. All known delays in signal cables and hardware were taken into account and possible errors were identified. Time of flight was measured by pulse fronts which, taking into account very large statistics, allowed the experiment to achieve good accuracy. It was found that the arrival of νμ is recorded ≈ 60 ns earlier than the calculated time in which light would cover the same distance in vacuum. In other words, the obtained velocity of νμ exceeded the speed of light by a relative value of (v-c)/c = (2.48 ± 0.28 (stat.) ± 0.30 (stat.)) × 10-5. Once this result has been published, numerous papers emerged attempting to justify superluminal velocities by postulating various hypothetical mechanisms. At the same time, attempts are made all the time to interpret the OPERA result in terms of non-exotic physical approaches. First of all, some not yet identified measurement errors are very probable. For example, according to the calculations of R. van Elburg (University of Groningen, the Netherlands) the GPS method does not take into account the relativistic effects of relative motion of the satellite and the beam, and the correction obtained by R. van Elburg — 64 ns -- is indeed very close to what is required. D.V. Naumov and V.A. Naumov (JINR, Dubna, Russia) explain the seemingly superluminal speeds by the flattish cross section of the wave packet of νμ and by a small angle offset of the beam axis from the detector axis. In another experiment, MINOS, the superluminal velocity of νμ was also reported but the statistical significance (v-c)/c = (5.1 ± 2.9) × 10-5 was very low. If (v-c)/c depends on the neutrino energy in an ordinary manner, the OPERA result also contradicts the observations of neutrinos from the SN 1987A supernova. Additional careful analysis is needed to clarify this situation, and independently run experiments may be needed. Source: arXiv:1109.4897v1 [hep-ex] Observation of the ðåð-neutrino1 November 2011The Borexino experiment at Gran Sasso (Italy) recorded for the first time solar neutrinos created in the reaction p + e- + p → 2H + νe with energy 1.442 MeV. Neutrinos were registered after their elastic scattering by electrons in ≈ 278 t of the liquid scintillator. A detailed analysis of the background and the anticoincidence technique used made it possible to exclude the background of cosmogeneous 11C to the maximum extent. These nuclei are formed when muons arriving with cosmic rays interact with 12C nuclei in the detector, and their β decays are the dominant source of background in the 1-2 MeV range. With the Mikheyev – Smirnov – Vol′fenstain effect taken into account at a large angle of mixing, the measured flux of ðåð neutrinos (1.6 ± 0.3) × 108 cm-2 s-1 fits well the standard model of solar structure (the ratio of the measured flow to the calculated value is 1.1 ± 0.2), whose predictions for a given type of neutrino are accurate within 1.2 %. Source: arXiv:1110.3230v1 [hep-ex] A new allotropic form of carbon1 November 2011Yu Tin (Stanford University, United States) and his colleagues have received a new carbon allotrope which like diamond has the sp3 structure of the electronic orbitals but unlike diamond has amorphous structure and isotropic hardness. Several allotropes of carbon are known. The new modification is derived by compressing glassy carbon between two diamond anvils to pressures of more than 40 GPa. The new modification inherited its loose structure from glassy carbon which exists as an array of curvilinear graphene-like fragments. The transformation of sp2 bonds to sp3 in the sample under compression was observed using methods of x-ray Raman spectroscopy with 1 eV resolution in the characteristic features of the spectrum corresponding to each type of bonding while the absence of crystal structure (amorphicity) was additionally confirmed by x-ray diffraction. The transition is reversible: carbon reverted to the original structure on lifting the pressure. In testing, a sphere of carbon of the new amorphous modification withstood unilateral pressure of 127 GPa at transverse confining pressure of 57 GPa, ie. the pressure difference was 70 GPa, which was previously achieved only with diamond specimens. Source: Phys. Rev. Lett. 107 175504 (2011) Brownian motion with memory1 November 2011It is typically assumed that molecules colliding with a Brownian particle produce random white-noise effect on its motion. A more accurate approach predicted that the motion of particles perturbs the liquid which should produce time correlations between movements of the particle (hydrodynamic memory). S. Jeney (École Polytechnique Fédérale de Lausanne — EPFL, Switzerland) and her colleagues from Germany and Switzerland have for the first time carried out monitoring of this effect in an experiment with single melamine micrometer-size spheres in an "optical tweezers" formed by focused beams of an infrared laser. Using the microscope, S. Jeney et al recorded the displacements of a microsphere in acetone solution with time resolution of ≈ 1 µs. Deviation from the white noise curve was observed in the spectrum of displacements of the microsphere, which corresponds to hydrodynamic memory. The authors of the experiment assume that their technique may prove applicable to designing new types of biosensors. Source: Nature 478 85 (2011) Gravitational redshift in galaxy clusters1 November 2011When light emitted by a galaxy leaves a massive cluster of galaxies, it undergoes the gravitational red shift. This shift is complementary to the cosmological red shift and to the Doppler shift caused by the peculiar and virial velocities. Researchers at the Niels Bohr Institute (Denmark) R. Wojtak, S.H. Hansen and J. Hjorth were the first to reveal this effect statistically over 7800 clusters in the sky survey SDSS Data Release 7. The virial motions of galaxies in the cluster cause symmetric line broadening, hence a large enough statistical array may allow identification of a small shift of the spectrum due to the gravitational potential of the clusters; this potential in its turn was found from the velocities of the galaxies of which they are composed. The results of the Danish researchers are consistent with the predictions of the general theory of relativity and f(R)-theories of gravitation at 90 % confidence level but contradict alternative tensor-vector-scalar (TeVeS) theories and modified Newtonian dynamics (MOND). Source: Nature 477 567 (2011) |
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 |