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| Issue 12, 2024 |
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Extracts from the Internet | ||
LHC experiment does not confirm the existence of tetraquark X(5568)1 May 2016It was reported earlier that discovered in a D0 experiment on Tevatron accelerator was a new particle - tetraquark X(5568) all of whose four quarks have different flavors (b,s,u,d), the X(5568) identification significance being estimated at the level of 5.1 σ. However, the search for this particle in the LHCb experiment failed to yield the result in spite of the fact that processed was a much larger data volume than that involved in the D0 experiment. The exotic hadrons X(5568) were sought by examining the spectrum of decaying B0s and π± particles that could be born by themselves upon X(5568) decays. No statistically significant excess of the number of events over the background testifying to X(5568) production was revealed, and restrictions from above on the X(5568) production rate were found. Source: http://cds.cern.ch/record/2140095/ Verification of the law of gravitation at submillimeter distances1 May 2016W.-H. Tan (Huazhong University of Science and Technology, China) with colleagues conducted a new experiment testing the Newtonian law of gravity (inverse-square law) at distances down to 295 µm. The deviation from this law was predicted in some versions of string theory and in M-theory. Oscillations of a torsion pendulum hanging on a thread and attracted by eight masses fixed on a rotating disc were measured. Calibration was reached through a dual compensation, i.e., an addition of mass on both the pendulum and the attractor, which reduced the role of errors in the determination of distances. The setup was located in a vacuum chamber and was thoroughly screened from electrostatic forces. The inverse-square law was checked in the assumption that the corrections to it have the form of the Yukawa potential V(r)=-Gm1m2(1+αexp[-r/λ])/r. Validity of the Newtonian law written as the condition |α|≤1 was confirmed down to λ=59 µm at a confidence level of 95%. The upper limits on the quantity α, which are the best for today, were obtained in the range λ≈70-300 µm. Source: Phys. Rev. Lett. 116 131101 (2016) Test of the quantum “free will theorem”1 May 2016In 2006 J.H. Conway and S.B. Kochen formulated the “free will theorem” in quantum mechanics (see Foundations of Physics 36 1441 (2006) and a stronger version of the theorem in Notices of the AMS 56 226 (2009)). The crucial point of the theorem is quantum nonlocality, quantum contextuality and the possibility of their combination in one experiment. The freedom of will is understood in the sense that if the experimenter has the freedom of choosing the measurement technique, the result of measurements on a particle does not depend under certain conditions on the whole previous history. B.-H. Liu (the University of Science and Technology of China, Hefei, China) with colleagues were the first to test this theorem experimentally. Pairs of photons in hyperentangled states appeared, i.e., entangled in two degrees of freedom, namely, in spatial paths and polarization. One of the photons of the pair was sent to the first laboratory where it underwent three successive measurements and the second photon was sent to the second laboratory where it was subjected to one measurement. On the basis of the data obtained it was possible to calculate the correlations between successive measurements taken at the first laboratory or between one of the measurements of the first and the measurement of the second laboratory. This was the way to check Einstein – Podolsky – Rosen correlations between the particle states at different laboratories and the violation of the Peres-Mermin inequalities describing noncontextuality. The results of measurements agree with high reliability with the free will theorem. From the practical point of view this proves the possibility of designing devices that simultaneously perform quantum calculations and provide quantum secure communication. Source: arXiv:1603.08254 [quant-ph] Heat capacity of photon gas under Bose – Einstein condensation1 May 2016The team of researchers from the University of Bonn (Germany) measured for the first time the change in the heat capacity of photon gas under its Bose – Einstein condensation. W. Weitz and his colleagues examined the photon gas between two mirrors spaced at a distance of the order of the photon wavelength. The cavity between them was filled with dye whose particles scattered and re-emitted photons, which led to photon gas thermalization. In such a system, the photon gas was quasi-two-dimensional and was effectively described by the equations for an almost ideal gas of massive particles — bosons. Varying the setup parameters one could change the Bose – Einstein condensation temperature within some limits around room temperature at which the experiment was carried out. This is how the set of experimental points above and below the condensation temperature was obtained. Photons were pumped into the medium by a laser, and the photon gas temperature was found through measuring the photon wavelength distribution. As expected, at a temperature near the Bose – Einstein condensation temperature the curve of specific heat has a cusp singularity similar to the one near the λ-point in liquid helium. Source: Nature Communications 7 11340 (2016) Gamma ray emission of young galaxies1 May 2016Gamma-ray emission from the young radio galaxy PKS 1718-649 was registered by the Fermi-LAT gamma-ray telescope in the range of 0.1-100 GeV. It had been predicted before that charged particle fluxes of emerging radio bursts into galaxies must in the course of inverse Compton scattering generate gamma-ray emission. It was registered for the first time at a confidence level of >5 σ through processing the Fermi-Lat data. Thus, young radio galaxies form a separate class of cosmic gamma-ray sources, and observations in the gamma-ray range will help to find the physical conditions in their compact radio bursts interacting with the galactic medium. The Fermi-LAT also registered gamma-ray emission from the ultra-bright IR galaxy Arp 220 located at a distance of 77 Mpc. The Arp 220 spectrum testifies to a high rate of star formation and, accordingly, to a large cosmic-ray particle flux accelerated in supernova remnants. For this reason Arp 220 galaxy was a priori expected to be the source of gamma-ray emission generated in the interaction of cosmic rays with interstellar medium. This gamma-ray emission with energy above 200 MeV was registered at a confidence level of 6.3 σ. From the gamma-ray luminosity of Arp 220 the efficiency of energy transfer from supernova remnants to cosmic rays — 4.2 ± 2.6 % was found for the first time for cosmic rays with energies above 1 GeV. Sources: arXiv:1604.01987 [astro-ph.HE], arXiv:1603.06355 [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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