Бодров Денис Алексеевич

Search for the decay 𝐵0→𝛾⁢𝛾 using Belle and Belle II data

2024 в печати · ARTICLE · en

Test of light-lepton universality in τ decays with the Belle II experiment

2024 в печати · ARTICLE · en

We present a measurement of the ratio of branching fractions of the τlepton decaying to muons or electrons using data collected with the Belle II detector at the SuperKEKB e+e− collider. The sample has an integrated luminosity of 362 ± 2 fb−1 at a centre-of-mass energy of 10.58 GeV. Using an optimised event selection, a binned maximum likelihood fit is performed using the momentum spectra of the electron and muon candidates. The result, Rμ = 0.9675 ± 0.0007 ± 0.0036, where the first uncertainty is statistical and the second is systematic, is the most precise to date. It provides a stringent test of the light-lepton universality, translating to a ratio of the couplings of the muon and electron to the W boson in τ decays of 0.9974 ± 0.0019, in agreement with the standard model expectation of unity.

New graph-neural-network flavor tagger for Belle II and measurement of sin 2⁢𝜙1 in 𝐵0→𝐽/𝜓⁢𝐾0S decays

2024 в печати · ARTICLE · en

We present GFlaT, a new algorithm that uses a graph-neural-network to determine the flavor of neutral 𝐵 mesons produced in ϒ⁡(4⁢𝑆) decays. It improves previous algorithms by using the information from all charged final-state particles and the relations between them. We evaluate its performance using 𝐵 decays to flavor-specific hadronic final states reconstructed in a 362 fb−1sample of electron-positron collisions collected at the ϒ⁡(4⁢𝑆) resonance with the Belle II detector at the SuperKEKB collider. We achieve an effective tagging efficiency of (37.40 ±0.43 ±0.36%), where the first uncertainty is statistical and the second systematic, which is 18% better than the previous Belle II algorithm. Demonstrating the algorithm, we use 𝐵0 →𝐽/𝜓⁢𝐾0S decays to measure the mixing-induced and direct 𝐶⁢𝑃 violation parameters, 𝑆 =(0.724 ±0.035 ±0.009) and 𝐶 =(−0.035 ±0.026±0.029).

Search for a 𝜇+⁢𝜇− resonance in four-muon final states at Belle II

2024 в печати · ARTICLE · en

Search for lepton-flavor-violating τ− → μ−μ+μ− decays at Belle II

2024 в печати · ARTICLE · en

We present the result of a search for the charged-lepton-flavor violating decay τ− → μ−μ+μ− using a 424 fb−1 sample of data recorded by the Belle II experiment at the SuperKEKB e+e− collider. The selection of e+e− → τ+τ− events is based on an inclusive reconstruction of the non-signal tau decay, and on a boosted decision tree to suppress background. We observe one signal candidate, which is compatible with the expectation from background processes. We set a 90% confidence level upper limit of 1.9 × 10−8 on the branching fraction of the τ− → μ−μ+μ− decay, which is the most stringent bound to date.

Measurement of the branching fractions of B→ D(*)KKs* and B→ D(*)Ds decays at Belle II

2024 в печати · ARTICLE · en

Measurements of the branching fractions of Ξ0c→ Ξ0π0, Ξ0c→ Ξ0η, and Ξ0c→ Ξ0η′ and asymmetry parameter of Ξ0c→ Ξ0π0

2024 в печати · ARTICLE · en

Tau physics at Belle and Belle II

2024 · ARTICLE · en

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.

Measurement of the Michel parameters in leptonic τ-decays at Super Tau-Charm facility

2024 · ARTICLE · en

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.

A test of lepton flavor universality with a measurement of R(D*) using hadronic tagging at the Belle II experiment

2024 в печати · ARTICLE · en

The ratio of branching fractions 𝑅⁡(𝐷*) =ℬ⁡(¯𝐵 →𝐷*⁢𝜏−⁢¯𝜈𝜏)/ℬ⁡(¯𝐵 →𝐷*⁢ℓ−⁢¯𝜈ℓ), where ℓ is an electron or muon, is measured using a Belle II data sample with an integrated luminosity of 189 fb−1 at the SuperKEKB asymmetric-energy 𝑒+⁢𝑒− collider. Data is collected at the ϒ⁡(4⁢S) resonance, and one 𝐵meson in the ϒ⁡(4⁢S) →𝐵⁢¯𝐵 decay is fully reconstructed in hadronic decay modes. The accompanying signal 𝐵 meson is reconstructed as ¯𝐵 →𝐷*⁢𝜏−⁢¯𝜈𝜏 using leptonic 𝜏 decays. The normalization decay, ¯𝐵→𝐷*⁢ℓ−⁢¯𝜈ℓ, produces the same observable final-state particles. The ratio of branching fractions is extracted in a simultaneous fit to two signal-discriminating variables in both channels and yields 𝑅⁡(𝐷*) =0.262+0.041−0.039⁢(stat)+0.035−0.032⁢(syst). This result is consistent with the current world average and with Standard Model predictions.