Пахлова Галина Владимировна

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

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.