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| Issue 12, 2024 |
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Extracts from the Internet | ||
Neutrino mass1 September 2024Observation of neutrino oscillations shows that the neutrino ν has a mass mν. Although the differences of mass squared of different ν mass states are measured with increasing accuracy [1], the absolute scale of mν is still unknown. Cosmology and experiments searching for neutrinoless double β-decay only give an indirect limit on the sum of ν. masses. A direct way of measuring mν is an analysis of β-decay near the kinematic endpoint of the energy spectrum using a high-resolution spectrometer [2, 3]. Such measurements were carried out at the Institute for Nuclear Research RAS (INR RAS) under the guidance of V M Lobashev and in the experiment in Mainz (Germany) and were continued in the international KATRIN experiment (Germany) with participation of researchers from INR RAS. The KATRIN Collaboration presented the results of recording 36 million electrons from the decays T2 → 3He T++e−+anti-ν [4]. The limit on the mass of the electron anti-ν was by a factor of two better than the previous result and is now mν<0.45 eV. Measuring mν is important for clarifying the fundamental issues in elementary particle physics. Neutrino is approximately six orders of magnitude lighter than other fermions, which may point to a new mass generation mechanism including sterile ν. [1] Kolupaeva L D, Gonchar M O, Ol’shevskii A G, Samoylov O B Phys. Usp. 66 753 (2023); UFN 193 801 (2023) [2] Bilen’kii S M Phys. Usp. 46 1137 (2003); UFN 173 1171 (2003) [3] Simkovic F Phys. Usp. 64 1238 (2021); UFN 191 1307 (2021) [4] Aker M et al., arXiv:2406.13516 [nucl-ex] Solar neutrino detection in experiments searching for dark matter (DM) particles1 September 2024Several underground laboratories are currently searching for DM (hidden Universe mass) particles by the effect of their possible scattering by atomic nuclei. However, in the same experiments, ν , born in the Sun and in other sources, must experience an elastic coherent scattering by the nuclei [5]. These ν create a background, called a “neutrino fog”, which has not been detected earlier. Z Bo (Shanghai Jiao Tong University, China) and their co-authors reported that they managed to register for the first time the “neutrino fog” in PandaX-4T experiment performed in the China Jinping underground laboratory [6]. The PandaX-4T detector contains 3.7 tones of liquid xenon and is designed for searching for DM particles. The measured flux of ν, that experienced an elastic coherent scattering by Xe nuclei, is consistent with the 2.6 σ significance with the expected flux of solar ν born in reactions with 8B nuclei in the pp-cycle. A similar result with statistical significance of 2.7 σ was also obtained in the XENONnT experiment at the Gran Sasso National Laboratory (Italy). Although the DM detectors have not been initially intended for ν detection, the possibility of such recording opens new useful channels for investigation. [5] Akimov D Yu et al. Phys. Usp. 62 166 (2019); UFN 189 173 (2019) [6] Bo Z et al., arXiv:2407.10892 [hep-ex] The cluster structure of GaTa4Se81 September 2024The lacunar spinel GaTa4Se8 is interesting in that it has properties of Mott insulator at room temperature and becomes a superconductor at 5.8 K, its superconductivity being perhaps of exotic topological character. M Magnaterra (University of Cologne, Germany) and their co-authors used the method of resonant inelastic X-ray scattering at a thallium boundary to prove that GaTa4Se8 has a cluster quasi-molecular structure [7]. The electrons in it are delocalized over the Ta4 tetrahedron, forming quasi-molecular spin-orbital Jtet=3/2 moments. The intracluster interactions mix the electron orbitals, reducing the effective constant of spin-orbital coupling by one third. Owing to mixing, the cluster wave function is sensitive to structural changes caused, for instance, by the external pressure or chemical substitution. This property of GaTa4Se8 and other compounds of this family may find useful technical applications. [7] Magnaterra M et al. Phys. Rev. Lett. 133 046501 (2024) Quantum Mpemba effect1 September 2024The Mpemba effect, observed in several experiments, is a situation when an initially hotter system cools faster than a cold system. Colloidal systems also showed an inverse Mpemba effect with a faster heating from a colder initial state. Quantum analogs of the Mpemba effect, which are due to quantum entanglement and fluctuations, were considered theoretically. A group of researchers from the Weizmann Institute (Israel) demonstrated for the first time the inverse quantum Mpemba effect for a single qubit on the basis of 88Sr+ ion in a thermal photon bath [8]. The ion with a higher degree of coherence underwent decoherence (heated up) and restored balance with the surroundings faster than the ion with a lower initial coherence. Moreover, a cold qubit could heat up exponentially faster than a warm qubit, thus demonstrating the strong version of the Mpemba effect. The direct quantum Mpemba effect was also discovered in a chain of 12 ions in another experiment [9] examining the time of symmetry restoration under a more or less strong initial deviation from the symmetric state. [8] Shapira S A et al. Phys. Rev. Lett. 133 010403 (2024) [9] Joshi L K et al. Phys. Rev. Lett. 133 010402 (2024) Cygnus X-31 September 2024The X-ray source Cygnus X-3 has attracted great attention for nearly 50 years already owing to its unusual properties, in particular, powerful bursts in the radio range and gamma-ray emission [10]. The source is presumably a binary system consisting of a Wolf – Rayet star and a compact object (a black hole or a neutron star) at a distance of ≈ 9.7 kpc from the Earth. In the IXPE (Imaging X-ray Polarimetry Explorer) observations, a polarization of X-rays from Cygnus X-3 was revealed for the first time [11] and the radiation mechanism was clarified. During an active X-ray phase within the range of 2-8 keV, the degree of linear polarization reaches 20.6 ± 0.3 %, it is orthogonal to the direction of radio emission, and at 3.5-6 keV is almost energy-independent. These properties are indicative of the X-ray flux collimation with a half-angle of ≤15°, determined, probably, by a funnel in an optically thick medium. In the polarization signal, dominant is the part of the accretion disc radiation, reflected from the funnel internal region. Collimation testifies, in turn, to gas accretion in the supercritical regime, when the radiation flux exceeds the Eddington limit. With allowance for the value of the opening angle, the object luminosity in the range of 2-8 keV makes up ≥ 5,5 × 1039 erg s−1 and, thus, Cygnus X-3 may be attributed to the class of ultraluminous X-ray sources. [10] Vladimirskii B M, Gal’per A M, Luchkov B I, Stepanyan A A Sov. Phys. Usp. 28 153 (1985); UFN 145 255 (1985) [11] Veledina A et al. Nat. Astron. 8 1031 (2024) |
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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