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| Issue 4, 2024 |
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Extracts from the Internet | ||
Higgs boson decay to a Z boson and a photon1 June 2023After the discovery in 2012 of the Higgs boson in ATLAS and CMS experiments performed at the Large Hadron Collider, this boson has been actively examined and some of its properties predicted by the Standard Model have already been tested [1]. In the Standard Model, the Higgs boson is of fundamental importance as being responsible for the appearance of mass in other elementary particles. The combination of data of the same ATLAS and CMS experiments for the period of 2015-2018 made it possible to register for the first time with a rather high fidelity of 3,4 σ another predicted rare process of Higgs boson decay to a Z boson and a photon proceeding with a probability of only 1.5 × 10−3 for the Higgs boson mass near 125 GeV [2]. The data on pp-collisions with energy of 13 TeV in the center-of-mass system were used. Z boson was registered by its decay into pairs e+e- and μ+μ-. The measured Z boson decay probability (3.4 ± 1.1) × 10−3 is consistent with the theoretical expectation within 1.9 σ. The analysis of the H → Zγ decay channel is important, in particular, because the intermediate virtual states of the indicated channel may contain a contribution of new particles and interactions [3]. [1] Heinemann B, Nir Y Phys. Usp. 62 920 (2019) ; UFN 189 985 (2019) [2] Conference materials LHCP-2023 [3] Kazakov D I Phys. Usp. 62 364 (2019); UFN 189 387 (2019) A test of quantum electrodynamics with exotic atoms1 June 2023A test of strong-field quantum electrodynamic theory is of interest for the search for new effects and, perhaps, manifestations of new physics beyond the Standard Model. An alternative to multicharged ions is the study of muon atoms, in which one of the electrons is replaced by a muon (for exotic atoms, see [4]). Because of its large mass, the muon orbital is 207 times closer to the nucleus, where the field is 40000 time stronger. T. Okumura (Physical and Chemical Research Institute RIKEN, Japan) and their co-authors have examined the X-ray spectra of muon neon – a system of a neon nucleus and a muon [5], occurring upon a low-pressure collision of a muon beam with a gaseous neon. The 5g → 4f and 5f → 4d transition energy was measured using superconducting X-ray detectors (transition edge sensors – TES). The choice of these levels is explained by a rather large distance from the nucleus, which reduces correction for the nucleus size. This gave a perfect agreement with the theoretical predictions. In particular, the strong-field vacuum polarization effect was verified to within 5.8 %. The precision of the results obtained is comparable with the precision of the test of strong-field quantum electrodynamics with multicharged uranium ions. [4] Men'shikov L I, Eseev M K Phys. Usp. 44 135 (2001); UFN 171 149 (2001) [5] Okumura T et al. Phys. Rev. Lett. 130 173001 (2023) α-particle monopole transition1 June 2023In many cases, the complex structure of strong interactions fails to give complete theoretical predictions of phenomena in nuclear physic. The studies of S Kegel (Johannes Gutenberg University Mainz, Germany) and their co-authors of helium nuclei (α-particle) excitations confirm that, in this case, the theoretical calculations are not consistence with experiment [6]. Transitions between the ground level O+1 of α-particle and the first excited level O+2 (monopole transitions) were examined on the Mainz microtron (MAMI), where an electron beam collided with cold helium nuclei, and the spectrum of the scattered electrons with momenta Q2=0.5-5 fm−2 was measured. The calculations in the framework of the chiral effective field theory fail to reproduce the obtained monopole transition formfactor. This discrepancy has already been known for 10 years, but the accuracy of new measurements exceeds significantly the accuracy of the preceding measurements, which only covered some portions of the indicated interval Q2. The authors suppose that the difference can be explained by inaccuracies in the structure of nuclear Hamiltonian. The resonance level O+2 is interesting in its location only a little higher than the nucleus decay energy, and it is not yet clear now whether the helium nucleus at the O+2 level is a predominantly collective four-nucleon excitation, or it is a molecular state of a proton and a tritium nucleus. [6] Kegel S et al. Phys. Rev. Lett. 130 152502 (2023) Spiral spin liquid1 June 2023Unusual spin structures (skyrmions etc.) are important both from the fundamental viewpoint and for their potential application in new technologies [7-9]. A spiral spin liquid, i.e., a correlated paramagnetic state, formed by fluctuating spin spirals, now remains a poorly investigated structure. It was theoretically predicted in Heisenberg’s models J1-J2 but has not yet been experimentally observed. The difficulty in its registration lies in the fact that substances have much more chances to transfer to other more typical magnetic states. J.N. Graham (University of Birmingham, Great Britain and Laue-Langevin Institute, France) and their co-authors used neutron scattering by a polycrystalline sample to discover for the first time the spiral spin liquid in the compound LiYbO2 [10]. Spiral contours corresponding to the spiral spin liquid were revealed on the diffusion scattering maps. The existence of this state was also evidenced by the measured spin-spin correlation functions. [7] Borisov A B Phys. Usp. 63 269 (2020); UFN 190 291 (2020) [8] Pervishko A A, Yudin D I Phys. Usp. 65 215 (2022); UFN 192 233 (2022) [9] Orlov Yu S et al. Phys. Usp. 66(7) (2023); UFN 193 689 (2023) [10] Graham J N et al. Phys. Rev. Lett. 130 166703 (2023) Ring-like structures in the center of galaxy M871 June 2023The Event Horizon Telescope observations of 2017 at a wavelength of 1.3 mm revealed a ring-like structure around the black hole (BH) in the center of the galaxy M87. This structure is assumed to be formed by gravitationally lensed radiation from the central region. R.-S. Lu (Shanghai Astronomical Observatory, China and Max Planck Institute for Radio Astronomy, Germany) and their co-authors published the data of interferometric observations of the same region, carried out with several radio telescopes at a wavelength of 3.5 mm [11]. Thanks to an improved data processing technique, the achieved resolution was 4 times higher than that in the previous observations. At the wavelength of 3.5 mm, one can see a ring-like structure with diameter of 8.4+0.5-1.1 Schwarzschild radii of the BH, which is 50 % larger than that at a wave of 1.3 mm. The new ring-like structure is interpreted as synchrotron radiation of accreted matter with absorption. Furthermore, a transition region from a ring-like structure to a relativistic jet was observed for the first time. Near the BH, the jet was somewhat wider than expected, which is indicative of a possible effect of wind from an accretion flow. For the BH silhouette in M87, see [12]. [11] Lu Ru-Sen et al. Nature 616 686 (2023) [12] Dokuchaev V I, Nazarova N O Phys. Usp. 63 583 (2020); UFN 190 627 (2020) |
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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