Extracts from the Internet

Triple W bosonproduction

Rare events of three W-boson production in one process were registered for the first time at the Large Hadron Collider in CERN [1]. Collisions of protons at a center-of-mass energy of 13 TeV were recorded by the ATLAS detector. WWW events were singled out with statistical significance of 8σ using 139 fb−1 of the database. Such events have never been reliably revealed before because of the small cross section of inclusive production pp→ WWW. The measured cross section turned out to be by 2.6 σ larger than predicted by theoretical calculations. At the given stage, this divergency may be thought of insignificant. The pp→ WWW process is sensitive to self-interaction of intermediate bosons and to other effects, and therefore considerable deviations from the Standard Model predictions might testify to a contribution of the “new physics” [2, 3]. This shows the importance of the study in this direction. Russian researchers from several scientific institutions are affiliated with the ATLAS Collaboration. [1] Aad G et al. Phys. Rev. Lett. 129 061803 (2022) [2] Gninenko S N, Krasnikov N V, Matveev V A Phys. Usp. 64 1286 (2021); UFN 191 1361 (2021) [3] Boos E E Phys. Usp. 65 (7) (2022); UFN 192 697 (2022)

Spin noise spectroscopy

Magnetization fluctuation (spin noise) spectra contain important information about the properties of different materials [4, 5]. One of the spin noise detection methods is measuring noises of Faraday rotation – polarization twist of a probing beam crossing a sample. This approach was earlier considered to be inapplicable to optically anisotropic crystals because of polarization distortion. V.S. Zapasskii (St. Petersburg State University) and his colleagues showed [6] both theoretically and experimentally that the problem only concerns homogeneous crystals, whereas in media with random uncorrelated inhomogeneities (spin fluctuations) the Faraday rotation noises are not suppressed, and the spin noise spectroscopy remains an efficient research method. This conclusion was experimentally verified with CaWO4 and LiYF4 crystals activated by Nd3+ ions. Crystals were put into a cryostat at a temperature of 3 K in a magnetic field, and lasing-induced transitions between Nd3+ levels were examined. The experiment has confirmed that anisotropy does not affect seriously the spin noise measurement. The physical research method “spin noise spectroscopy” was developed by E.B. Aleksandrov and V.S. Zapasskii in 1981 [7]. The results obtained open new possibilities for its application in optically anisotropic and inhomogeneous media. [4] Zapasskii V S, Kozlov G G Phys. Usp. 60 628 (2017); UFN 187 675 (2017) [5] Smirnov D S, Mantsevich V N, Glazov M M Phys. Usp. 64 923 (2021); UFN 191 973 (2021) [6] Kozlov V O et al. Phys. Rev. Lett. 129 077401 (2022) [7] Aleksandrov E B, Zapasskii V S Ñ Sov. Phys. JETP 54 64 (1981); ZhETF 81 132 (1981)

Angle-resolved photoemission spectroscopy and the Fermi surface

Angle-resolved photoemission spectroscopy (ARPES) appeared exactly 100 years ago and became one of the basic research methods in solid state physics [8]. S. Borisenko (G.W. Leibniz Institute for Solid State and Materials Research and Fermiologics Company, Germany) and his co-authors have updated the ARPES methods within a short time period to obtain high-resolution 3D images of the Fermi surface [9]. An electron lens was placed between the sample and detector, which heightened the angular resolution. The second key point was a negative cutoff potential a bit lower than the threshold photoelectron energy. This allowed measuring their spectrum with high accuracy. The experiments realizing these ideas have demonstrated measurement of 3D Fermi surface in the TiTe2 compound and detailed 2D Fermi surface measurements in several superconductors, topological insulators, and other substances. [8] Maksimov E G, Savrasov S Yu Sov. Phys. Usp. 33 763 (1990); UFN 160 155 (1990) [9] Borisenko S et al. Nature Communications 13 4132 (2022)

Josephson effect at the atomic scale

In 1966, I. Kuluk showed [10] that the presence of spin states in a tunnel junction between superconductors can reverse a of the Josephson current flow by a phase shift by π. This effect was observed in mesoscopic systems, but at the atomic scale a similar effect, known as the “Yu-Shiba-Rusinov state”, had not been realized before. S. Karan (Max Planck Institute for Solid State Research) and their co-authors performed a new experiment [11], to observe the Yu-Shiba-Rusinov State for the first time. A magnetic impurity was placed at the endpoint of a superconducting vanadium needle drawn near a superconducting sample. This device differs from the conventional SQUID by the absence of a loop. Instead, the phase shift is realised through a quantum phase transition inducing a destructive interference of two transport channels and reversing supercurrent between the needle and the sample, which is indicative of the Yu-Shiba-Rusinov state. The Josephson effect at the atomic scale may find application in quantum sensors and in investigation of superconductivity mechanisms. [10] Kulik I JETP 22 841 (1966); ZhETF 49 1211 (1965) [11] Karan S et al. Nature Physics 18 893 (2022)

Periodicity in the fast radio burst FRB 20191221A

The generation mechanism of fast radio bursts, i.e., millisecond radio signals from space, has not yet been clarified. One of the hypotheses suggests bursts on neutron stars – magnetars [12]. B.C.πAndersen (McGill University, Canada) and her co-authors from CHIME/FRB Collaboration detected a fast radio burst FRB 20191221A with a total duration of about 3 s, which contains nine components separated by time intervals multiple of 217πms [13]. The statistical significance of the discovered periodicity is 6.5 σ, and the large measure of burst dispersion points to its extragalactic origin. Although sources of repeated bursts with nonrigorous periodicity are already known, so fast periodicity as that of FRB 20191221A has not yet been observed. This testifies in favor of the model [14] of burst generation directly in the magnetosphere of a rotating neutron star (like galactic radio pulsar bursts, but much more powerful) and restricts models where bursts are generated in more distant regions. [12] Popov S B, Postnov K A, Pshirkov M S Phys. Usp. 61 965 (2018); UFN 188 1063 (2018) [13] Andersen B C et al. Nature 607 256 (2022) [14] Popov S B, Postnov K A, arXiv:0710.2006 [astro-ph]

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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.

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