 |
RSS feeds |
|
|||||
| Issue 4, 2024 |
|
||||||
|
|
|
||||||
Extracts from the Internet | ||
Charge radius of muonic deuteron1 September 2016In the 2010 CREMA experiment, the proton charge radius in muonic hydrogen was found to be by 4% smaller than in ordinary hydrogen. This discrepancy has not yet been explained. As distinct from ordinary hydrogen, it is a muon rather than an electron that revolves around the proton in muonic hydrogen. R. Pohl (Max Planck Institute of Quantum Optics, Germany) with colleagues from the same collaboration CREMA took new measurements, but this time with muonic deuterium μd. A muon beam was directed to a vessel with gaseous deuterium where muons were trapped into μd atoms and the Lamb shift very sensitive to the nuclear charge radius was measured by the spectroscopic method. The measured nuclear charge radius rd=2.12562(78) fm was by 7.5 standard deviations less than the CODATA-2010 catalogue value and by 3.5σ less than the CREMA collaboration value obtained for ed. This discrepancy is analogous to that obtained earlier in the comparison of electronic and muonic hydrogen. Possibly, to explain the revealed discrepancies one should specify the theoretical calculations, but the contribution of the effects beyond the Standard Model is not excluded. Source: Science 353 669 (2016) Neutrino studies1 September 2016New data on the neutrino properties were obtained in three experiments. Studied in the T2K experiment were νμ and anti-νμ oscillations in a beam that had passed from the accelerator J-PARC in Tokai (Japan) to the underground detector Super-Kamiokande at a distance of 295 km. 32 νe and anti-νe were registered, whereas 23 and 7, respectively, were expected provided that CP invariance is not violated. Thus, indications of the maximum CP invariance violation in neutrino oscillations were obtained for the first time, although the probability of statistical fluctuation now remains high, ≈1/20. In another experiment NOvA, ν oscillations are also studied in a beam propagating from the Fermilab accelerator to the detector located at a distance of 810 km. The measurements showed for the first time that in the third mass state unequal contributions from muon and tau flavors are possibly present. This effect is called a “non-maximal mixing”. However a large set of statistics is needed for its reliable confirmation. The IceCube detector located in the ice of the South Pole is used to seek oscillations of atmospheric νμ and anti-νμ to sterile neutrinos. No signals corresponding to sterile neutrinos were detected, which narrows the possible parameter space for such neutrinos. Russian researchers from a number of scientific organizations take part in the international experiments T2K, NOvA and IceCube. Sources: T2K, Fermi National Accelerator Laboratory, Phys. Rev. Lett. 117 071801 (2016) Programmable quantum computer1 September 2016Prototypes of quantum computers consisting of several connected qubits have already been demonstrated earlier, but they have been configured only to implement particular planned programs. C. Monroe (University of Maryland in College-Park, USA) with colleagues was the first to design a quantum computer that can be reprogrammed for working with different algorithms. The computer consists of a chain of five ytterbium ions 171Yb+ entrapped in a radio-frequency Paul trap. The states of zero and unity were coded by sublevels of a hyperthin splitting of the level 2S1/2. Using sequences of laser pulses one can change the ion states by setting required sequences of quantum operations and the states (the results of quantum calculations) were read by exciting cyclic transitions 2S1/2-2P1/2 and registering fluorescent radiation. The pair interaction of ions was realized through their spin-spin interaction and transverse collective motion of ions in the chain. On this computer, the Deutsch-Jozsa and Bernstein-Vazirani algorithms were implemented and the quantum Fourier expansion was first demonstrated which plays an important role in quantum calculations. On account of quantum superposition of states future quantum computers will be able to solve some problems with an exponentially higher velocity than conventional classical computers. Source: Nature 536 63 (2016) Room-temperature muon supercurrent1 September 2016B. Hillebrands (Kaiserslautern University of Technology, Germany) and his colleagues carried out an experiment in which supercurrent was observed, perhaps for the first time, in room-temperature Bose-Einstein condensate of magnons (quasi-particles – spin wave quanta). Supercurrent was observed earlier only at room temperature in the case of superconductivity and superfluidity. The Bose-Einstein magnon condensate was obtained in a room-temperature ferromagnetic Y3Fe5O12 film through parametric pumping. Laser pulses excited a local temperature gradient in the film which induced the phase shift of the condensate wave function and the divergent magnon flux registered using Brillouin spectroscopy. The flux characteristics turned out to be well consistent with the theoretical predictions for a magnon supercurrent. However, the existence of supercurrent is called in question and the demonstration of a dissipationless magnon flux might become a decisive proof. Source: Nature Physics, online publication of August 1, 2016. Search for dark matter particles1 September 2016The origin of dark matter which makes up approximately 27% of the Universe mass is not yet clear. According to one of the basic hypotheses dark matter consists of weakly interacting massive particles (WIMPs), and they are directly or indirectly being sought in a number of experiments. Presented are the new results of investigations on one of the most sensitive underground detectors Large Underground Xenon (LUX) trying to register the interaction between WIMPs flying through the Earth and 127Xe nuclei. No excess of signals over the background was revealed, which imposed new constraints on the interaction cross section. Also presented are new results of the search for annihilation gamma-ray emission by the array of ground-based Cherenkov detectors HESS (High Energy Stereoscopic System). The central part of the Galaxy with radius of 300 pc was observed where the dark matter density is expected to be high and, accordingly, the annihilation must be effective. The HESS data do not show a statistically significant excess of signal over the background either, which imposes constraints on the annihilation cross section. Near the mass of 1.5 TeV for annihilation to W+W- pairs the value ⟨σannv⟩<6×10-26 cm3 s-1 was obtained. Thus, according to the data of ground-based measurements the constraints approached for the first time the value ⟨σannv⟩ corresponding to thermal WIMP production in the early Universe. Source: arXiv:1608.07648 [astro-ph.CO], arXiv:1607.08142 [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. | |
|
© 1918–2024 Uspekhi Fizicheskikh Nauk Email: ufn@ufn.ru Editorial office contacts About the journal Terms and conditions |