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| Issue 12, 2024 |
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Extracts from the Internet | ||
Unconventional gamma-resonance in LHC experiments1 February 2016In ATLAS and CMS experiments on Large Hadron Collider, the diphoton distribution showed a maximum which has not yet been convincingly explained. ATLAS registered this resonance at an energy of 750 GeV in 14 event containing a pair of photons, the statistical significance being (2.3-3.9) σ (depending on the assumptions on the process structure). The recorded CMS resonance decaying into two photons has a peak at 760 GeV. It was distinguished with significance of (2.0-2.6) σ in 10 events. In theoretical works, a number of hypotheses concerning the origin of the discovered resonance were suggested. This resonance, if it is not due to statistical fluctuation, can be a slight indication of the existence of new particles. For example, it may correspond to a boson resembling the heavy version of Higgs boson. It is also possible that the resonance is related to a heavy particle among the decay products of which dark matter particles (hidden mass of the Universe) can exist. Sources: arXiv:1512.04933 [hep-ph], arXiv:1512.07616 [hep-ph] Feishbach resonance for two-electron fermions1 February 2016Two independent groups of researches applied Feishbach orbital resonance to control the pair interaction of atoms - fermions 173Yb where each atom has two valence electrons. Feishbach resonance for such atoms was earlier considered to be impossible because the resultant spin of the electrons is zero, but R. Zhang with colleagues proposed a new type of Feishbach resonance, namely, the orbital resonance. In experiments carried out using their method, the magnetic field causes the mixing of the singlet and triplet states 1S0 and 3P0 of 173Yb atoms in an ultracold gas in an optical grating, which is responsible for the coupling between the spin and orbital degrees of freedom. Furthermore, the energy difference of magnetic interaction for nuclei that are in different spin states (Zeeman effect) was used. The combination of spin states of electrons and nuclei made it possible to reach resonance. L. Fallani (the University of Florence, Italy) and his colleagues observed resonance by the character of gas cloud expansion, and S. Folling (Ludwig Maximilian University of Munich, Germany) with colleagues studied thermalization in gas after its local heating. The thermalization rate is proportional to the atomic scattering cross section and, accordingly, to the strength of atomic interaction. Both the groups revealed that this strength is maximum in a magnetic field of about 50 G. Sources: Phys. Rev. Lett. 115 265301 (2015), Phys. Rev. Lett. 115 265302 (2015) Autonomous Maxwell demon on a chip1 February 2016J.P. Pekola (Aalto University, Finland) and his colleagues from Finland, Russia and USA realized experimentally an autonomous Maxwell demon (the control device from the thought experiment considered by J.C. Maxwell in 1867). The Maxwell demons designed earlier consumed energy from alien sources. However, the conception of an autonomous Maxwell demon operating at the expense of internal forces only has been discussed beginning with L. Szilard’s works. The setup of J.P. Pekola and his colleagues consists of a single-electron transistor and auxiliary elements placed on an electron chip. The superconducting aluminum contacts were attached to a nanometer lead island. If an electron tunnels from the contact to the island, a positive potential is generated which confines this electron. If, on the contrary, an electron tunnels from the island, a negative potential appears. Owing to this, the electron always overcomes the potential barrier, and under quantum tunneling the system gets cooler. These processes are an equivalent of an open and closed door for fast and slow molecules in the original Maxwell demon conception. The work of a demon was shown to lead to his temperature rise, which in accordance with R. Landauer’s principle is a thermodynamic cost of information on the presence of electrons. Source: Phys. Rev. Lett. 115 260602 (2015) Borophene1 February 2016A.J. Mannix (Argonne National Laboratory, USA) with colleagues synthesized deep in vacuum a one-atom-thick crystal layer of boron on a silver substrate. This layer resembling graphene was called “borophene”, but as distinct from graphene, free borophene without a substrate is most likely to be unstable. Deposition of boron atoms onto silver proceeded at a temperature of 450 to 700°C and the structures obtained were investigated by a scanning tunnel microscope and by the electron diffraction method. The borophene crystal lattice has a rectangular configuration that showed structures resembling a unification of different-scale atomic clusters with out-of-plane bulging. As distinct from bulk boron allotropes borophene possesses highly anisotropic metal properties: it is a conductor along the layer and a semiconductor across the layer. The mechanical properties of borophene are predicted to be also highly anisotropic. Source: Science 350 1513 (2016) Jet base in galaxy M871 February 2016In cores of galaxies with active nuclei, particle jets are formed that are ejected far beyond the galaxies. The mechanisms of generation and collimation of these jets have not yet been completely clarified. The main role is assumed to be played by the magnetic field in the interior parts of accretion discs around supermassive black holes. Making use of VLBI and Green Bank radio telescopes K. Hada (National Astronomical Observatory of Japan and National Institute for Astrophysics, Italy) with colleagues investigated the jet base (the starting portion) at a frequency of 86 GHz (3.5 mm) in galaxy M87. The joint observation of two telescopes allowed a decrease of the effect of atmospheric fluctuations making noise at this wavelength and a resolution of ∼10 Schwarzschild radii (RS) of the central black hole. The specific features of jet structure known from observations at lower frequencies were confirmed and new specificities were revealed. Bright spots with limbs can be seen at distances of ∼10RS to 28RS from the core where the jet opening angle is ∼100°. At distances of ∼35RS the jet opening angle decreases to ∼60° and then the jet has a conic shape down to ∼84RS, and at larger distances it undergoes collimation according the parabolic law. At distances of ∼35RS the jet cross section is locally shrinking and again increases. A weak counter jet is also observed. Comparison of the velocities in a jet (∼0.32c$) and a counter jet (∼0.17c$) gave the estimate of the angle at which the jet can be seen (29°-45°). This value is higher than that given by examination of optical kinematics by the Hubble telescope (11°-19°) probably because of the curvature of the optical marker trajectory. The polarimetric measurements at a wave of 86 GHz were taken for the first time for this source. In some jet regions its radiation is weakly polarized (at a level of ∼(3-4)%), but highly polarized (∼20%) structures are also seen that are indicative of the presence of an ordered magnetic field. Source: arXiv:1512.03783 [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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