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| Issue 11, 2024 |
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Extracts from the Internet | ||
Weak charge of the proton1 November 2013The Qweak collaboration of the T. Jefferson laboratory (Newport-news, USA) determined for the first time the weak charge (i.e. the charge of the weak interaction) of the proton by measuring the asymmetry of elastic scattering pe- for the small quantity of momentum transferred. The spin-polarized beams e- were sent at the liquid hydrogen target and the characteristics of beam scattering (depending on the weak charge) were compared with the spins e- directed along the velocity vector of e- and along the opposite vector. The obtained asymmetry parameter was Aep = ( -279 ± (stat) ± 31(syst)) × 10-9. Using the proton form factors taken from the results of other experiments, the weak charge of the proton QWp = 0.064 ± 0.012 was calculated. This value is found to be in good agreement with the prediction of the Standard Model QWp(SM) = 0.0710 ± 0.0007. The weak charge was successfully determined by using only 4 % of the data collected in the Qweak experiment and this error is expected to reduce by a factor of about 5 in the course of subsequent analysis. Measuring the weak charge is a promising direction of searching for new effects beyond the confines of the Standard Model of elementary particles. Source: Phys. Rev. Lett. 111 141803 (2013) Quantum meta-material1 November 2013P. Macha (the Institute of Photon Technologies and the Karlsruhe Technological Institute in Germany) and his colleagues in Germany and Russia have created a meta material which is an array of 20 qubits (quantum bits) based on superconducting Josephson junctions. In the past, meta materials were designed only of classical (non-quantum) elements. A qubit array was placed in a microwave resonator. Owing to the inductive connection between qubits and the resonator, the problem of dephasing of qubits owing to their unavoidable spread in parameters was solved. As a result, the qubit array could have unified resonance frequencies: the ground frequency of the resonator and its' harmonics. It was shown in the experiment that the meta material changes the frequency and the phase of the signals passing through it. Note that the signal produced collective effect simultaneously on up to eight qubits. The use of superconducting elements with low losses in this low-loss meta material imparts unique properties to it, and promises practical utilization, for instance, in unit photon detectors. Source: arXiv:1309.5268 [quant-ph] Photon “molecule”1 November 2013A group of researchers headed by M. Lukin (Harvard University) and V. Vuletich (Massachusets Institute of Technology) observed the formation of bound pairs of photons in ultra-cold gas of Rubidium atoms. A laser pulse excited in the gas a collective Rydberg state. This state forms when the electron is distributed between highly excited levels of several neighboring atoms simultaneously. The propagation of a given electromagnetic excitation can be interpreted as motion of a photon possessing some efficient mass through a medium of photons. Owing to the effect of Riedberg blockade, the second such excitation could not be generated in immediate vicinity of the first. However, the second photon could follow the first if it formed a bound state resembling a photon “molecule”. Photons in such pairs interacted one with the other not directly but via a non-linear medium. Measurements showed that photons escaped from the atomic trap simultaneously, i.e. the photons moved through the medium as a bound entity. The bound states of photons could be used in quantum logical devices, as they are in optical elements of classical quantum (not quantum) computers. Source: Nature 502 71 (2013) Bound states of magnons1 November 2013T. Fukuhara (M. Planck Institute of Quantum Optics, Germany) et al. observed experimentally the effect, predicted by Hans Bethe in 1931, of magnons merging into pairs of magnons (a magnon is a quasiparticles constituting excitation in a system of interacting spins). Earlier pairs of magnons were established only indirectly, in the spectra of solids. In the new experiments, the atoms of ultra-cold gas of 87Rb were built into a one-dismensional potential barrier at whose central segments magnons were excited. Two directions of spin corresponded to two sublevels of hyperfine splitting. As the potential barrier started to be lowered, magnons would start moving along the chains and sometime later experimenters would again raise the barrier, fixing magnons in their new positions. Magnons were recorded via observing them in the field of the microscope excited by the laser light of the fluorescent emission from atoms; they depended on their spin state. This technique allowed the experimenters to observe the position of individual magnons to the accuracy of one cell of the lattice. By calculating the spacial correlation functions it was shown that in addition to individual magnons, moving pairs were also detected in addition to individual magnons. Also, the mean time of decay for bound pairs of magnons — about 210 ms — were also measured for the decay of the magnons. This time is dictated by the scattering of magnons on inhomogenuities created by thermal fluctuations. Source: Nature 502 76 (2013) Search for gamma lines in the data of Fermi-LAT1 November 2013In addition to experiments on direct detection of particles of dark matter which so far yielded no unequivocal interpretation, attempts were made to indirect detection of dark matter particles by searching for a signal generated when these particles annihilate. An interesting direction is a search for monochromatic lines corresponding to the channel of annihilation to two photons. A detection of such lines would provide decisive arguments in favor of the presence of an annihilation signal produced by dark matter. Certain indication to a line at an energy 133 GeV were obtained in observations of the orbital Fermi-LAT gamma telescope. The Fermi-LAT collaboration has performed a new processing of the data collected over 4.4 years of observations carried out with a view to test the presence of such lines. The lines were sought in the energy range from 5 to 300 GeV in 5 patches in the neighborhood of the galactic center. If a small excess of gamma radiation near the energy 133 GeV is indeed observed locally at reliability level of 2.9 σ then the reliability over the entire set of data from all patches drops to 1 σ. In view of such low reliability, the presence of a gamma line at an energy 133 GeV in the region of galactic center has not been confirmed yet, and the suspected peculiarities in the spectrum may prove to be mere statistical fluctuations. Source: arXiv:1310.2953 [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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