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| Issue 6, 2024 |
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Extracts from the Internet | ||
Large Hadron Collider (LHC) tests of W-boson1 May 2024The W-boson mass mW and its decay width ΓW may include corrections from the processes beyond the Standard Model. For instance, in supersymmetric theories, W-boson has additional channels of decay into particles – the lightest superpartners of gauge bosons. Thus, mW and ΓW measurements are of importance for seeking effects beyond the Standard Model. Calculations within its framework give mWSM = 80355 ± 6 MeV and ΓWSM = 2088 ± 1 MeV. In different experiments, including LHC ones, several mW measurements were performed showing some discrepancy between the results. The value of ΓW was also measured earlier with LEP and Tevatron accelerators. The ATLAS collaboration has performed a new analysis of LHC data on pp collisions with an energy of 7 TeV in the center-of-mass system using the modified methods of data processing to obtain the most precise state-of-the-art numerical values mW = 80366.5 ± 15.9 MeV and ΓW = 2202 ± 47 MeV, which agree rather well with the prediction of the Standard Model and do not yet contain hints at new physics [1]. [1] Aad G et al. (ATLAS Collaboration), arXiv:2403.15085 Search for rare neutron decays1 May 2024The problem of discrepancy between the lifetime of neutrons (n) in a vessel and in a beam has been known for already 30 years. In particular, oscillations of n into mirror n have been considered as a solution to this problem [2]. In 2018, B Fornal and B Grinstein put forward a hypothesis of a “dark decay (DD) of n” with the birth of very weakly interacting particles, possibly constituting the dark matter in the Universe. M Pfutzner and K Riisager have shown that a sensitive method for searching for DD is to study the decay of neutron-rich nuclei. M Le Joubioux (Large Heavy Ion National Accelerator (GANIL), France) and their co-authors performed a new experiment with 6He nuclei having a halo of two n [3]. The process 6He→4He+n+χ was sought, where χ is an unobservable particle, and the emission of single n is only possible in the presence of DD (the probability of other channels is exceedingly low). The isotopes 6He, obtained on GANIL, were trapped into an aluminum target and were scanned by a low-threshold neutron counter. The flux of n did not exceed the background level, which allowed for estimating the probability of the process as ≤ 4.0×10−10. For the DD probability, this gives the restriction ≤ 10−5. Depending on the χ mass, the new restriction is stronger than the previous ones by one or several orders of magnitude and excludes a considerable range of parameters, which might explain the problem of n lifetime. [2] Berezhiani Z, Bento L Phys. Rev. Lett. 96 081801 (2006) [3] Le Joubioux M et al. Phys. Rev. Lett. 132 132501 (2024) Tunneling in graphene1 May 2024Although electrons in graphene effectively behave like massless particles, their propagation differs from processes in conventional optics. In particular, the effect of an ideal passage through a barrier (Klein tunneling) and an ideal reflection (antiKlein tunneling) are possible. The first process was earlier observed in graphene only indirectly and the second one was not found at all. These processes were registered reliably for the first time by M M Elahi (University of Virginia, USA) and their co-authors in the graphene Carbino disk with a concentric p−n junction at a fixed radial distance between internal and external electrodes [4]. The Klein and antiKlein tunneling at the junction were observed respectively in graphene monolayer and bilayer by the presence of local maximum and minimum of magnetoconductance. The experiment confirmed some theoretical predictions, for example, angular spots (Brewster angles) and shift of magnetoconductance maxima with increasing doping density were revealed in bilayer graphene. [4] Elahi M M et al. Phys. Rev. Lett. 132 146302 (2024) A new nonlinear optical effect in heavy water1 May 2024A group of researchers from A M Prokhorov Institute of General Physics RAS and B I Stepanov Institute of Physics, NAS (Republic of Belarus) revealed a new nonlinear optical phenomenon arising in the SRS-laser pumping pulse (laser on the basis of stimulated Raman scattering) in heavy water [5]. The radiation was focused into a cuvette with heavy water, and the transmitted radiation was observed on the screen and was investigated with a spectrograph. The motion of the beam caustic from the volume to the surface was accompanied by the growth of SRS threshold. At the beam waist depth of 3 mm the SRS threshold increased to ≈2 TW cm−2, which initiated an optical breakdown with a shock wave and an upward drop ejection. A 20-fold breakdown energy lowering was due to self-focusing with front shortening to an avalanche ionization and a breakdown. The work was supported by the RSF grant 23-42-10019 together with the grant F23RFN-040 of Belorussia. The revealed new effect may find useful practical applications in biotechnology and medicine, as well as in creation of a jet thrust in a Bunkin-Prokhorov engine [6]. [5] Pershin S.M. et al. Bulletion of the Lebedev Physics Institute Vol. 3 (2024) [6] Bunkin F V, Prokhorov A M Sov. Phys. Usp. 19 561 (1976); UFN 119 425 (1976) Baryon acoustic oscillations1 May 2024The effect of baryon acoustic oscillations (BAO), predicted by A D Sakharov in 1965, is very important for cosmological studies. In particular, the problem of Hubble tension was confirmed using this effect. BAO are sound waves in baryon-photon liquid in the epoch before hydrogen recombination, which show up in a large-scale distribution of galaxies and quasars. The DESI (Dark Energy Spectroscopic Instrument) collaboration, which performs spectroscopic observations with a 4-meter telescope, presented new results of BAO observations of 5.7 mln galaxies and quasars at redshifts 0.1 < z < 2.1 [7]. The BAO measurement accuracy reaches already ≈ 0.52 %, and the statistical significance of their discovery at z = 0.93 makes up 9.1 σ. At z < 0.8, a certain systematic difference with the Planck satellite data (of 2018) was noticed. The main result was the construction of a high-precision distance scale connecting local and cosmological “standard rulers”. [7] Adame A G et al. (DESI Collaboration), arXiv:2404.03000 |
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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