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Measurement of the Michel parameters in leptonic τ-decays at Super Tau-Charm facility
International Journal of Modern Physics A. 2024. Vol. 39. No. 26n27. Article 2442019.
Bodrov D., Pakhlov P.
We present a new method for direct measurement of all Michel parameters in the 𝜏− → 𝜇− 𝜈_𝜇 𝜈_𝜏 decay related to the polarization of the daughter muon: 𝜉′, 𝜉′′, 𝜂′′, 𝛼′/𝐴, and 𝛽′/𝐴. The method is based on the reconstruction of the muon decays-in-flight in the tracker of the 𝑒+𝑒− collider experiments and relies on the correlation between muon spin and its daughter electron momentum. The low probability of decay-in-flight in the tracker volume is compensated by the unprecedented statistics of modern flavor factories, which ultimately leads to the possibility of achieving high accuracy. We discuss the application of the suggested method in the experiments at 𝑒+𝑒− colliders and present a feasibility study for the future Super Charm-Tau Factory experiment. We also discuss the result of the first use of the proposed method in the Belle experiment, confirming its applicability.
Publication based on the results of:
Antsiferov P.S., Stepanov L.V., Matiukhin N. D., Review of Scientific Instruments 2025 Vol. 96 No. 12 Article 123506
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Radiation from rotational transitions of CO molecules in distant galaxies creates a chaotic background with an intensity reaching 1000 Jy/sr at a wavelength of approximately 1 mm. This background will pose a serious problem, when measuring spectral distortions of the cosmic microwave background, in particular, the mu-distortion, which presumably has an intensity of less than ...
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discovery of bright diamond-based SPS created by nature. It is shown that narrow (≤2 nm) lines observed in the
500-800 nm range in photoluminescence (PL) spectra of the surface layer of untreated Yakut diamonds rich in
nitrogen and hydrogen are linked to ...
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Chiral semiconductor nanostructures and nanoparticles are promising materials for applications in biological sensing, enantioselective separation, photonics, and spin-polarized devices. Here we performed a detailed analysis of optical properties of chiral CdSe nanoplatelets with thickness of 2 and 3 monolayers (ML) with Nacetyl-L-cysteine ligands. We studied the absorption spectra peculiarities, analyzed time-resolved photoluminescence and investigated circular ...
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Smirnov A., Mantsevich V. N., Saitov S. R. et al., Journal of Applied Physics 2026 Vol. 139 Article 185702
This work presents a comprehensive investigation into the temperature-dependent thermally stimulated conductivity and photoconductivity of vacuum-annealed thin films based on core–shell CdSe/CdS nanoplatelets passivated with oleic acid ligands. Controlled thermal annealing under vacuum conditions leads to a substantial increase in both dark and photoinduced conductivity, which is primarily attributed to partial desorption of the ligands. ...
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The Journal of Physical Chemistry Letters 2026 Vol. 17 No. 18 P. 5386–5394
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Kolokolov I., Lebedev V., Physical Review E - Statistical, Nonlinear, and Soft Matter Physics 2026 Vol. 113 Article 054117
We theoretically investigate the correlation functions of the phase of a light wave propagating through a
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Гущина В. А., Mendeleev Communications 2025 Vol. 35 No. 2 P. 193–195
All-inorganic perovskite CsPbBr3 and Cs4PbBr6 nanoparticles are intensively studied for their unique optical properties, though synthesizing single-phase nanoparticles has posed challenges. Detailed synthesis method of CsPbBr3 and Cs4PbBr6 single-phase nanoparticles and their chemical and phase analysis are described. Distinctive optical characteristics, such as photoluminescence, optical band gap and the Urbach tail region, are revealed and explained within the current ...
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Гущина В. А., Physics of Complex Systems, Russia 2026 Vol. 7 No. 1 P. 3–15
Heterostructures based on ZnO nanorods and CsPbBr3 nanocrystals were investigated for their potential as semiconductor SERS substrates. We found that ZnO morphology governs the efficiency of interfacial energy transfer, leading to enhanced photoluminescence under 390 nm excitation and a noticeable reduction of the bandgap in the composites. Raman analysis revealed a pronounced intensity enhancement and ...
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Bisnovatyi-Kogan G., Kondratyev I., Moiseenko S. G., International Journal of Modern Physics A 2025 Vol. 40 No. 7 Article 2550018
Bright transient objects in different wave bands have been discovered in recent years.
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Toropina O. D., Bisnovatyi-Kogan G. S., Moiseenko S. G., Astronomy Reports 2025 Vol. 69 No. 1 P. S80–S90
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Morozov E. V., Demin A. S., Borovitskaya I. V. et al., Inorganic Materials: Applied Research 2026 Vol. 17 No. 3 P. 619–626
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Added: May 4, 2026
Bodrov D., International Journal of Modern Physics A 2024 Article 2442006
In this paper, we present the major results obtained in tau physics by the Belle and Belle II experiments. For the Belle II experiment, we also discuss prospects for improved measurements of the tau lepton properties, new results in Michel parameters determination, and searches for CP and lepton °avor violation in tau decays. ...
Added: October 30, 2024
Bodrov D., Pakhlov P., Adachi I. et al., Physical Review D - Particles, Fields, Gravitation and Cosmology 2023 Vol. 108 No. 1 Article 012003
We present the first measurement of the Michel parameter ξ′ in the τ−→μ−¯νμντ decay using the full data sample of 988 fb−1 collected by the Belle detector operating at the KEKB asymmetric energy e+e− collider. The method is based on the reconstruction of the μ−→e−¯νeνμ decay-in-flight in the Belle central drift chamber and relies on the correlation between muon spin and its daughter electron momentum. We ...
Added: September 17, 2023
D. Bodrov, P. Pakhlov, Adachi I. et al., Physical Review Letters 2023 Vol. 131 No. 2 Article 021801
We report the first measurement of the Michel parameter ξ′ in the τ−→μ−¯νμντ decay with a new method proposed just recently. The measurement is based on the reconstruction of the τ−→μ−¯νμντevents with subsequent muon decay in flight in the Belle central drift chamber. The analyzed data sample of 988 fb−1 collected by the Belle detector corresponds to approximately 912×106 τ+τ−pairs. We measure ξ′=0.22±0.94(stat)±0.42(syst), which is in ...
Added: September 17, 2023
Bodrov D., Pakhlov P., Bulletin of the Lebedev Physics Institute 2023 Vol. 50 No. 4 P. 144–149
A method for measuring all Michel parameters describing the daughter muon polarization in the tau(-) -> mu(-) (nu(mu)) over bar nu(tau) decay, i.e., xi', xi", eta", alpha'/A, and beta'/A, is discussed. The application of the method to the future Super Charm-Tau Factory experiment is considered. The statistical uncertainties expected by the full data statistics (10 ...
Added: September 17, 2023
Bodrov D., Physics of Atomic Nuclei 2021 Vol. 84 No. 2 P. 212–215
In this paper, we present a feasibility study of the first measurement of the longitudinal polarization of a muon from the tau-lepton decay to extract the Michel parameter xi' at the future Super Charm-Tau Factory (SCTF). The expected number of muon decays events on the full SCTF data was estimated, possible background processes were studied, and methods ...
Added: October 26, 2021