Бодров Денис Алексеевич

A new method for the measurement of the Michel parameters that describe the daughter muon polarization in the tau(-) -> mu(-) (nu)over-bar(mu) nu(tau) decay

2022 · ARTICLE · en

В данной статье дается подробное описание метода первого прямого измерения всех параметров Мишеля в распде τ → μντ, связанных с поляризацией дочернего мюона. Рассмотрено применение предложенного метода в существующих и будущих экспериментах на e+e- коллайдерах. Мы выполнили оценки чувствительности будущих экспериментов Super Charm-Tau Factory и Belle II. Для первого оценивается чувствительность к параметрам Мишеля ξ′, ξ′′, η′′, α′/A и β′/A. Для последнего рассматривается только один параметр Мишеля ξ′, для которого чувствительность максимальна.

Search for the decay B0s→η′K0S

2022 · ARTICLE · en

We report the results of the first search for the decay B0s→η′K0S using 121.4 fb−1 of data collected at the Υ(5S) resonance with the Belle detector at the KEKB asymmetric-energy e+e− collider. We observe no signal and set a 90% confidence-level upper limit of 8.16×10−6 on the B0s→η′K0S branching fraction.

Study of γγ→γψ(2S) at Belle

2022 · ARTICLE · en

Measurement of Two-Particle Correlations of Hadrons in e+e− Collisions at Belle

2022 · ARTICLE · en

The measurement of two-particle angular correlation functions in high-multiplicity e+e− collisions at √s=10.52 GeV is reported. In this study, the 89.5 fb−1 of hadronic e+e− annihilation data collected by the Belle detector at KEKB are used. Two-particle angular correlation functions are measured in the full relative azimuthal angle (Δϕ) and three units of pseudorapidity (Δη), defined by either the electron beam axis or the event-shape thrust axis, and are studied as a function of charged-particle multiplicity. The measurement in the thrust axis analysis, with mostly outgoing quark pairs determining the reference axis, is sensitive to the region of additional soft gluon emissions. No significant anisotropic collective behavior is observed with either coordinate analyses. Near-side jet correlations appear to be absent in the thrust axis analysis. The measurements are compared to predictions from various event generators and are expected to provide new constraints to the phenomenological models in the low-energy regime.

First measurement of the Λ+c→pη′ decay

2022 · ARTICLE · en

We present the first measurement of the branching fraction of the singly Cabibbo-suppressed (SCS) decay Λ+cΛ�+ → pη′ with η′ → ηπ+π−, using a data sample corresponding to an integrated luminosity of 981 fb−1, collected by the Belle detector at the KEKB e+e− asymmetric-energy collider. A significant Λ+cΛ�+ → pη′ signal is observed for the first time with a signal significance of 5.4σ. The relative branching fraction with respect to the normalization mode Λ+cΛ�+ → pK−π+ is measured to be B(Λ+c→pη′)B(Λ+c→pK−π+)=(7.54±1.32±0.73)×10−3,�(Λ�+→��′)�(Λ�+→��−�+)=(7.54±1.32±0.73)×10−3, where the uncertainties are statistical and systematic, respectively. Using the world-average value of B(Λ+c→pK−π+)�(Λ�+→��−�+) = (6.28 ± 0.32) × 10−2, we obtain B(Λ+c→pη′)=(4.73±0.82±0.46±0.24)×10−4,�(Λ�+→��′)=(4.73±0.82±0.46±0.24)×10−4, where the uncertainties are statistical, systematic, and from B(Λ+c→pK−π+)�(Λ�+→��−�+), respectively.

Search for B0 meson decays into Λ and missing energy with a hadronic tagging method at Belle

2022 · ARTICLE · en

We present a search for the decays of B0 mesons into a final state containing a Λ baryon and missing energy. These results are obtained from a 711 fb−1 data sample that contains 772×106 B¯B pairs and was collected near the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e− collider. We use events in which one B meson is fully reconstructed in a hadronic decay mode and require the remainder of the event to consist of only a single Λ. No evidence for these decays is found, and we set 90% confidence level upper limits on the branching fractions in the range 2.1–3.8×10−5. This measurement provides the world’s most restrictive limits, with implications for baryogenesis and dark matter production.

Search for a Light Higgs Boson in Single-Photon Decays of Υ(1S)Using Υ(2S)→π+π−Υ(1S) Tagging Method

2022 · ARTICLE · en

We search for a light Higgs boson (A0) decaying into a τ+τ− or μ+μ− pair in the radiative decays of Υ(1S). The production of Υ(1S) mesons is tagged by Υ(2S)→π+π−Υ(1S) transitions, using 158×106 Υ(2S) events accumulated with the Belle detector at the KEKB asymmetric energy electron-positron collider. No significant A0 signals in the mass range from the τ+τ− or μ+μ− threshold to 9.2 GeV/c2 are observed. We set the upper limits at 90% credibility level (C.L.) on the product branching fractions for Υ(1S)→γA0 and A0→τ+τ− varying from 3.8×10−6 to 1.5×10−4. Our results represent an approximately twofold improvement on the current world best upper limits for the Υ(1S)→γA0(→τ+τ−) production. For A0→μ+μ−, the upper limits on the product branching fractions for Υ(1S)→γA0 and A0→μ+μ− are at the same level as the world average limits, and vary from 3.1×10−7 to 1.6×10−5. The upper limits at 90% credibility level on the Yukawa coupling fΥ(1S) and mixing angle sinθA0 are also given.

Combined analysis of Belle and Belle II data to determine the CKM angle ϕ3 using B+ → D(KS0 h+h-)h+ decays

2022 · ARTICLE · en

We present a measurement of the Cabibbo-Kobayashi-Maskawa unitarity triangle angle ϕ3 (also known as γ) using a model-independent Dalitz plot analysis of B+ → D (K0S��0h+h−)h+, where D is either a D0 or D¯¯¯¯�¯0 meson and h is either a π or K. This is the first measurement that simultaneously uses Belle and Belle II data, combining samples corresponding to integrated luminosities of 711 fb−1 and 128 fb−1, respectively. All data were accumulated from energy-asymmetric e+e− collisions at a centre-of-mass energy corresponding to the mass of the Υ(4S) resonance. We measure ϕ3 = (78.4 ± 11.4 ± 0.5 ± 1.0)°, where the first uncertainty is statistical, the second is the experimental systematic uncertainty and the third is from the uncertainties on external measurements of the D-decay strong-phase parameters.

Search for tetraquark states Xccss in D+sD+s (D∗+sD∗+s) final states at Belle

2022 · ARTICLE · en

A search for double-heavy tetraquark state candidates Xcc¯s¯s decaying to D+sD+s and D*+sD*+s is presented for the first time using the data samples of 102×106 Υ(1S) and 158×106 Υ(2S) events, and the data samples at √s=10.52, 10.58, and 10.867 GeV corresponding to integrated luminosities of 89.5, 711.0, and 121.4 fb−1, respectively, accumulated with the Belle detector at the KEKB asymmetric energy electron-positron collider. The invariant-mass spectra of the D+sD+s and D*+sD*+s are studied to search for possible resonances. No significant signals are observed, and the 90% confidence level upper limits on the product branching fractions [B(Υ(1S,2S)→Xcc¯s¯s+anything)×B(Xcc¯s¯s→D+sD+s(D*+sD*+s))] in Υ(1S,2S) inclusive decays and the product values of Born cross section and branching fraction [σ(e+e−→Xcc¯s¯s+anything)×B(Xcc¯s¯s→D+sD+s(D*+sD*+s))] in e+e− collisions at √s=10.52, 10.58, and 10.867 GeV under different assumptions of Xcc¯s¯s masses and widths are obtained.

Study of B0→D+h- (h=K/π) decays at Belle

2022 · ARTICLE · en

We present a measurement of the branching fractions of the Cabibbo favored ¯B0→D+π− and the Cabibbo suppressed ¯B0→D+K− decays. We find B(¯B0→D+π−)=(2.48±0.01±0.09±0.04)×10−3 and B(¯B0→D+K−)=(2.03±0.05±0.07±0.03)×10−4 decays, where the first uncertainty is statistical, the second is systematic, and the third uncertainty is due to the D+→K−π+π+ branching fraction. The ratio of branching fractions of ¯B0→D+K− and ¯B0→D+π− is measured to be RD=[8.19±0.20(stat)±0.23(syst)]×10−2. These measurements are performed using the full Belle dataset, which corresponds to 772×106B¯B pairs and use the Belle II software framework for data analysis.