Бодров Денис Алексеевич

Measurement of CP asymmetries in B0→η′K0s decays at Belle II

2024 в печати · ARTICLE · en

We describe a measurement of charge-parity (𝐶⁢𝑃) violation asymmetries in 𝐵0 →𝜂′⁢𝐾0S decays using Belle II data. We consider 𝜂′ →𝜂⁡( →𝛾⁢𝛾)⁢𝜋+⁢𝜋− and 𝜂′ →𝜌⁡( →𝜋+⁢𝜋−)⁢𝛾 decays. The data were collected at the SuperKEKB asymmetric-energy 𝑒+⁢𝑒− collider between the years 2019 and 2022, and contain (387 ±6) ×106 bottom-antibottom meson pairs. We reconstruct 829 ±35 signal decays and extract the 𝐶⁢𝑃 violating parameters from a fit to the distribution of the proper-decay-time difference between the two 𝐵 mesons. The measured direct and mixing-induced 𝐶⁢𝑃 asymmetries are 𝐶𝜂′⁢𝐾0S =−0.19 ±0.08 ±0.03 and 𝑆𝜂′⁢𝐾0S =+0.67 ±0.10 ±0.03, respectively, where the first uncertainties are statistical and the second are systematic. These results are in agreement with current world averages and standard model predictions.

Search for the baryon number and lepton number violating decays τ−→Λπ− and τ−→Λ¯π− at Belle II

2024 в печати · ARTICLE · en

We present a search for the baryon number 𝐵 and lepton number 𝐿 violating decays 𝜏− →Λ⁢𝜋− and 𝜏− →¯Λ⁢𝜋− produced from the 𝑒+⁢𝑒− →𝜏+⁢𝜏− process, using a 364 fb−1 data sample collected by the Belle II experiment at the SuperKEKB collider. No evidence of signal is found in either decay mode, which have |Δ⁢(𝐵 −𝐿)| equal to 2 and 0, respectively. Upper limits at 90% credibility level on the branching fractions of 𝜏− →Λ⁢𝜋− and 𝜏− →¯Λ⁢𝜋− are determined to be 4.7 ×10−8 and 4.3 ×10−8, respectively.

Measurement of branching-fraction ratios and CP asymmetries in B± → DCP±K± decays at Belle and Belle II

2024 в печати · ARTICLE · en

We report results from a study of B± → DK± decays followed by D decaying to the CP-even final state K+K− and CP-odd final state , where D is an admixture of D0 and states. These decays are sensitive to the Cabibbo-Kobayashi-Maskawa unitarity-triangle angle ϕ3. The results are based on a combined analysis of the final data set of 772 × 106pairs collected by the Belle experiment and a data set of 198 × 106 pairs collected by the Belle II experiment, both in electron-positron collisions at the Υ(4S) resonance. We measure the CP asymmetries to be CP+ = (+12.5 ± 5.8 ± 1.4)% and CP− = (−16.7 ± 5.7 ±0.6)%, and the ratios of branching fractions to be CP+ = 1.164 ± 0.081 ± 0.036 and CP− = 1.151 ± 0.074 ± 0.019. The first contribution to the uncertainties is statistical, and the second is systematic. The asymmetries CP+ and CP− have similar magnitudes and opposite signs; their difference corresponds to 3.5 standard deviations. From these values we calculate 68.3% confidence intervals of (8.5° ϕ3 °) or (84.5° ϕ3 °) or (163.3° ϕ3 °) and 0.321 rB

Measurement of branching fractions and direct 𝐶⁢𝑃 asymmetries for 𝐵→𝐾⁢𝜋 and 𝐵→𝜋⁢𝜋 decays at Belle II

2024 в печати · ARTICLE · en

We report measurements of the branching fractions and direct 𝐶⁢𝑃 asymmetries of the decays 𝐵0→𝐾+⁢𝜋−, 𝐵+ →𝐾+⁢𝜋0, 𝐵+ →𝐾0⁢𝜋+, and 𝐵0 →𝐾0⁢𝜋0, and use these for testing the standard model through an isospin-based sum rule. In addition, we measure the branching fraction and direct 𝐶⁢𝑃asymmetry of the decay 𝐵+ →𝜋+⁢𝜋0 and the branching fraction of the decay 𝐵0 →𝜋+⁢𝜋−. The data are collected with the belle II detector from 𝑒+⁢𝑒− collisions at the ϒ⁡(4⁢𝑆) resonance produced by the SuperKEKB asymmetric-energy collider and contain 387 ×106 bottom-antibottom meson pairs. Signal yields are determined in two-dimensional fits to background-discriminating variables, and range from 500 to 3900 decays, depending on the channel. We obtain −0.03 ±0.13 ±0.04 for the sum rule in agreement with the standard model expectation of zero and with a precision comparable to the best existing determinations.

First Measurement of 𝑅⁡(𝑋𝜏/ℓ) as an Inclusive Test of the 𝑏→𝑐⁢𝜏⁢𝜈 Anomaly

2024 в печати · ARTICLE · en

We measure the tau-to-light-lepton ratio of inclusive 𝐵-meson branching fractions 𝑅⁡(𝑋𝜏/ℓ)≡ℬ⁡(𝐵→𝑋⁢𝜏⁢𝜈)/ℬ⁡(𝐵→𝑋⁢ℓ⁢𝜈), where ℓ indicates an electron or muon, and thereby test the universality of charged-current weak interactions. We select events that have one fully reconstructed 𝐵 meson and a charged lepton candidate from 189 fb−1 of electron-positron collision data collected with the Belle II detector. We find 𝑅⁡(𝑋𝜏/ℓ)=0.228±0.016⁢(stat)±0.036⁢(syst), in agreement with standard-model expectations. This is the first direct measurement of 𝑅⁡(𝑋𝜏/ℓ).

Evidence for 𝐵+→𝐾+⁢𝜈⁢𝜈 decays

2024 в печати · ARTICLE · en

We search for the rare decay 𝐵+ →𝐾+⁢𝜈⁢¯𝜈 in a 362 fb−1 sample of electron-positron collisions at the ϒ⁡(4⁢𝑆) resonance collected with the Belle II detector at the SuperKEKB collider. We use the inclusive properties of the accompanying 𝐵 meson in ϒ⁡(4⁢𝑆)→𝐵⁢¯𝐵 events to suppress background from other decays of the signal 𝐵 candidate and light-quark pair production. We validate the measurement with an auxiliary analysis based on a conventional hadronic reconstruction of the accompanying 𝐵meson. For background suppression, we exploit distinct signal features using machine learning methods tuned with simulated data. The signal-reconstruction efficiency and background suppression are validated through various control channels. The branching fraction is extracted in a maximum likelihood fit. Our inclusive and hadronic analyses yield consistent results for the 𝐵+→𝐾+⁢𝜈⁢¯𝜈 branching fraction of [2.7±0.5⁢(stat)±0.5⁢(syst)] ×10−5 and [1.1+0.9−0.8⁢(stat)+0.8−0.5⁢(syst)] ×10−5, respectively. Combining the results, we determine the branching fraction of the decay 𝐵+ →𝐾+⁢𝜈⁢¯𝜈to be [2.3±0.5⁢(stat)+0.5−0.4⁢(syst)] ×10−5, providing the first evidence for this decay at 3.5 standard deviations. The combined result is 2.7 standard deviations above the standard model expectation.

Search for the 𝑒+⁢𝑒−→𝜂𝑏⁡(1⁢𝑆)⁢𝜔 and 𝑒+⁢𝑒−→𝜒𝑏⁢0⁡(1⁢𝑃)⁢𝜔 processes at √𝑠=10.745 GeV

2024 в печати · ARTICLE · en

We search for the 𝑒+⁢𝑒− →𝜂𝑏⁡(1⁢𝑆)⁢𝜔 and 𝑒+⁢𝑒− →𝜒𝑏⁢0⁡(1⁢𝑃)⁢𝜔 processes at a center-of-mass energy of 10.745 GeV, which is close to the peak of the ϒ⁡(10753) state. We use data collected by the Belle II experiment during a special run, corresponding to an integrated luminosity of 9.8 fb−1. We reconstruct 𝜔 →𝜋+⁢𝜋−⁢𝜋0 decays and use the 𝜔 meson’s recoil mass to search for the signals. We do not find evidence for either process, and set upper limits on the corresponding Born-level cross sections of 2.5 pb and 7.8 pb, respectively, at the 90% confidence level. The 𝜒𝑏⁢0⁡(1⁢𝑃)⁢𝜔 limit is the result of a combination of this analysis and a previous search using full reconstruction.

Search for Rare 𝑏→𝑑⁢ℓ+⁢ℓ− Transitions at Belle

2024 в печати · ARTICLE · en

Measurement of 𝐶⁢𝑃 asymmetries in 𝐵0→𝐾0𝑆⁢𝐾0𝑆⁢𝐾0𝑆 decays at Belle II

2024 в печати · ARTICLE · en

We report a measurement of decay-time-dependent charge-parity (𝐶⁢𝑃) asymmetries in 𝐵0→𝐾0𝑆⁢𝐾0𝑆⁢𝐾0𝑆 decays. We use 387×106 𝐵⁢¯𝐵 pairs collected at the ϒ⁡(4⁢𝑆) resonance with the Belle II detector at the SuperKEKB asymmetric-energy electron-positron collider. We reconstruct 220 signal events and extract the 𝐶⁢𝑃-violating parameters 𝑆 and 𝐶 from a fit to the distribution of the decay-time difference between the two 𝐵 mesons. The resulting confidence region is consistent with previous measurements in 𝐵0→𝐾0𝑆⁢𝐾0𝑆⁢𝐾0𝑆 and 𝐵0 →(𝑐⁢¯𝑐)⁢𝐾0 decays and with predictions based on the standard model.

Measurement of the branching fraction of the decay 𝐵−→𝐷0⁢𝜌⁢(770)− at Belle II

2024 в печати · ARTICLE · en