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Fodor, A. (ORCID:000000022821759X)

Publications and source records attributed to Fodor, A. (ORCID:000000022821759X).

13 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Measurement of 𝐡 + β†’πœ + ⁒𝜈 𝜏 branching fraction with a hadronic tagging method at Belle II

We present a measurement of the branching fraction of 𝐡 + β†’πœ + ⁒𝜈 𝜏 decays using 387Β±6Γ—10 6 ϒ⁑(4⁒𝑆) collected between 2019 and 2022 with the Belle II detector at the SuperKEKB 𝑒 + ⁒𝑒 βˆ’ collider. We reconstruct the accompanying 𝐡 βˆ’ meson using the hadronic tagging method, while 𝐡 + β†’πœ + ⁒𝜈 𝜏 candidates are identified in the recoil. We find evidence for 𝐡 + β†’πœ + ⁒𝜈 𝜏 decays at 3.0 standard deviations, including systematic uncertainties. The measured branching fraction is ℬ⁑(𝐡 + β†’πœ + ⁒𝜈 𝜏 )=[1.24Β±0.41⁒(stat)Β±0.19⁒(syst)]Γ—10 βˆ’4 .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Measurements of the branching fractions of ${\Xi }_{c}^{+}\to {\Sigma }^{+}{K}_{S}^{0}$, ${\Xi }_{c}^{+}\to {\Xi }^{0}{\pi }^{+}$, and ${\Xi }_{c}^{+}\to {\Xi }^{0}{K}+$ at Belle and Belle II

Using 983.0 fb βˆ’1 and 427.9 fb βˆ’1 data samples collected with the Belle and Belle II detectors at the KEKB and SuperKEKB asymmetric energy e + e βˆ’ colliders, respectively, we present studies of the Cabibbo-favored ${\Xi }_{c}^{+}$ decays ${\Xi }_{c}^{+}\to {\Sigma }^{+}{K}_{S}^{0}$ and ${\Xi }_{c}^{+}\to {\Xi }^{0}{\pi }^{+}$, and the singly Cabibbo-suppressed decay ${\Xi }_{c}^{+}\to {\Xi }^{0}{K}^{+}$. The ratios of branching fractions of ${\Xi }_{c}^{+}\to {\Sigma }^{+}{K}_{S}^{0}$ and ${\Xi }_{c}^{+}\to {\Xi }^{0}{K}^{+}$ relative to that of ${\Xi }_{c}^{+}\to {\Xi }^{-}{\pi }^{+}{\pi }^{+}$ are measured for the first time, while the ratio $\mathcal{B}({\Xi }_{c}^{+}\to {\Xi }^{0}{\pi }^{+})/\mathcal{B}({\Xi }_{c}^{+}\to {\Xi }^{-}{\pi }^{+}{\pi }^{+})$ is also determined and improved by an order of magnitude in precision. The measured branching fraction ratios are $\begin{array}{c}\frac{\mathcal{B}\left({\Xi }_{c}^{+}\to {\Sigma }^{+}{K}_{S}^{0}\right)}{\mathcal{B}\left({\Xi }_{c}^{+}\to {\Xi }^{-}{\pi }^{+}{\pi }^{+}\right)}=0.067\pm 0.007\pm 0.003,\\ \frac{\mathcal{B}\left({\Xi }_{c}^{+}\to {\Xi }^{0}{\pi }^{+}\right)}{\mathcal{B}\left({\Xi }_{c}^{+}\to {\Xi }^{-}{\pi }^{+}{\pi }^{+}\right)}=0.251\pm 0.005\pm 0.010,\\ \frac{\mathcal{B}\left({\Xi }_{c}^{+}\to {\Xi }^{0}{K}^{+}\right)}{\mathcal{B}\left({\Xi }_{c}^{+}\to {\Xi }^{-}{\pi }^{+}{\pi }^{+}\right)}=0.017\pm 0.003\pm 0.001.\end{array}$ Additionally, the ratio $\mathcal{B}({\Xi }_{c}^{+}\to {\Xi }^{0}{K}^{+})/\mathcal{B}({\Xi }_{c}^{+}\to {\Xi }^{0}{\pi }^{+})$ is measured to be 0.068 Β± 0.010 Β± 0.004. Here, the first and second uncertainties are statistical and systematic, respectively. Multiplying the ratios by the branching fraction of the normalization mode, $\mathcal{B}({\Xi }_{c}^{+}\to {\Xi }^{-}{\pi }^{+}{\pi }^{+})=(2.9\pm 1.3)%$, we obtain the following absolute branching fractions $\begin{array}{c}\mathcal{B}({\Xi }_{c}^{+}\to {\Sigma }^{+}{K}_{S}^{0})=(0.194\pm 0.021\pm 0.009\pm 0.087)\text{%},\\ \mathcal{B}({\Xi }_{c}^{+}\to {\Xi }^{0}{\pi }^{+})=(0.728\pm 0.014\pm 0.027\pm 0.326)\text{%},\\ \mathcal{B}({\Xi }_{c}^{+}\to {\Xi }^{0}{K}^{+})=(0.049\pm 0.007\pm 0.003\pm 0.022)\text{%},\end{array}$ where the third uncertainties are from $\mathcal{B}({\Xi }_{c}^{+}\to {\Xi }^{-}{\pi }^{+}{\pi }^{+})$.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Search for lepton-flavor-violating ${\tau }^{-}\to {{\ell}}^{-}{K}_{s}^{0}$ decays at Belle and Belle II

We present the results of a search for charged-lepton-flavor violating decays ${\tau }^{-}\to {{\ell}}^{-}{K}_{s}^{0}$, where β„“ βˆ’ is either an electron or a muon. We combine e + e βˆ’ data samples recorded by the Belle II experiment at the SuperKEKB collider (428 fb βˆ’1 ) with samples recorded by the Belle experiment at the KEKB collider (980 fb βˆ’1 ) to obtain a sample of 1.3 billion e + e βˆ’ β†’ Ο„ + Ο„ βˆ’ events. We observe 0 and 1 events and set 90% confidence level upper limits of 0.8 Γ— 10 βˆ’8 and 1.2 Γ— 10 βˆ’8 on the branching fractions of the decay modes ${\tau }^{-}\to {e}^{-}{K}_{S}^{0}$ and ${\tau }^{-}\to {\mu }^{-}{K}_{S}^{0}$, respectively. These are the most stringent upper limits to date.

beyond Standard Model↗
DOE OSTI2025

Search for Lepton-Flavor-Violating Decay Modes 𝐡 0 →𝐾$^0_𝑆$⁒𝜏 Β± ⁒ℓ βˆ“ with Hadronic 𝐡 Tagging at Belle and Belle II

We present the first search for the lepton-flavor-violating decay modes 𝐡 0 →𝐾$^0_𝑆$⁒𝜏 Β± ⁒ℓ βˆ“ (β„“=πœ‡,𝑒) using the 711 and 365 fb βˆ’1 data samples recorded by the Belle and Belle II detectors, respectively. We use a hadronic 𝐡-tagging technique to fully reconstruct a 𝐡 meson and search for signal decays in the system recoiling against the tagged meson, considering 𝜏 decays to either light leptons, one charged hadron, or one charged hadron and a neutral pion. We find no evidence for 𝐡 0 →𝐾$^0_𝑆$⁒𝜏 Β± ⁒ℓ βˆ“ decays and set 90% confidence level upper limits on the branching fractions in the range of [0.8,3.6] Γ—10 βˆ’5 .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Measurement of the time-integrated 𝐢⁒𝑃 asymmetry in 𝐷 0 β†’ 𝐾$^{0}_{S}$𝐾$^{0}_{S}$ decays using opposite-side flavor tagging at Belle and Belle II

We measure the time-integrated 𝐢⁒𝑃 asymmetry in 𝐷 0 β†’ 𝐾$^{0}_{S}$𝐾$^{0}_{S}$ decays reconstructed in 𝑒 + ⁒𝑒 βˆ’ β†’ $c\bar{c}$ events collected by the Belle and Belle II experiments. The corresponding data samples have integrated luminosities of 980 and 428 fb βˆ’1 , respectively. To infer the flavor of the 𝐷 0 meson, we exploit the correlation between the flavor of the reconstructed decay and the electric charges of particles reconstructed in the rest of the 𝑒 + ⁒𝑒 βˆ’ β†’ $c\bar{c}$ event. This results in a sample which is independent from any other previously used at Belle or Belle II. The result, 𝐴 𝐢⁒𝑃 ⁑(𝐷 0 β†’ 𝐾$^{0}_{S}$𝐾$^{0}_{S}$)=(1.3Β±2.0Β±0.2)%, where the first uncertainty is statistical and the second systematic, is consistent with previous determinations and with 𝐢⁒𝑃 symmetry.

CP violation↗
DOE OSTI2025

Measurement of the time-integrated 𝐢⁒𝑃 asymmetry in 𝐷 0 β†’ πœ‹ 0 β’πœ‹ 0 decays at Belle II

We measure the time-integrated 𝐢⁒𝑃 asymmetry, 𝐴 𝐢⁒𝑃 , in 𝐷 0 β†’ πœ‹ 0 β’πœ‹ 0 decays reconstructed in 𝑒 + ⁒𝑒 βˆ’ β†’ $𝑐⁒\bar{𝑐}$ events collected by Belle II during 2019–2022. The data corresponds to an integrated luminosity of 428 fb βˆ’1 . The 𝐷 0 decays are required to originate from the flavor-conserving 𝐷 *+ β†’ 𝐷 0 β’πœ‹ + decay to determine the charm flavor at production time. Control samples of 𝐷 0 β†’ 𝐾 βˆ’ β’πœ‹ + decays, with or without an associated pion from a 𝐷 *+ decay, are used to correct for detection asymmetries. The result, 𝐴 𝐢⁒𝑃 ⁑(𝐷 0 β†’ πœ‹ 0 β’πœ‹ 0 ) = (0.30 Β± 0.72 Β± 0.20)%, where the first uncertainty is statistical and the second systematic, is consistent with 𝐢⁒𝑃 symmetry.

CP violation↗
DOE OSTI2025

Model-independent measurement of 𝐷 0 βˆ’$\overline{D}$ 0 mixing parameters in 𝐷 0 β†’ 𝐾$^{0}_{𝑆}$β’πœ‹ + β’πœ‹ βˆ’ decays at Belle and Belle II

We perform a model-independent measurement of the 𝐷 0 βˆ’$\overline{D}$ 0 mixing parameters using samples of 𝑒 + ⁒𝑒 βˆ’ -collision data collected by the Belle and Belle II experiments that have integrated luminosities of 951 fb βˆ’1 and 408 fb βˆ’1 , respectively. Approximately 2.05 Γ— 10 6 neutral 𝐷 mesons are reconstructed in the 𝐷 0 β†’ 𝐾$^{0}_{S}$β’πœ‹ + β’πœ‹ βˆ’ channel, with the neutral 𝐷 flavor tagged by the charge of the pion in the 𝐷* + β†’ 𝐷 0⁒ πœ‹ + decay. Assuming charge-parity symmetry, the mixing parameters are measured to be π‘₯ = (4.0 Β±1.7 Β±0.4) Γ— 10 βˆ’3 and 𝑦 = (2.9 Β±1.4 Β±0.3) Γ— 10 βˆ’3 , where the first uncertainties are statistical and the second systematic. The results are consistent with previous determinations.

Charmed mesons↗
DOE OSTI2025

Measurement of the branching fraction, polarization, and time-dependent C P asymmetry in B 0 β†’ ρ + ρ βˆ’ decays and constraint on the CKM angle Ο• 2

We present a measurement of the branching fraction and fraction of longitudinal polarization of B 0 β†’ ρ + ρ βˆ’ decays, which have two Ο€ 0 ’s in the final state. We also measure time-dependent C P violation parameters for decays into longitudinally polarized ρ + ρ βˆ’ pairs. This analysis is based on a data sample containing ( 387 Β± 6 ) Γ— 10 6 Ο’ ( 4 S ) mesons collected with the Belle II detector at the SuperKEKB asymmetric-energy e + e βˆ’ collider in 2019–2022. We obtain B ( B 0 β†’ ρ + ρ βˆ’ ) = ( 2.8 9 βˆ’ 0.22 + 0.23 βˆ’ 0.27 + 0.29 ) Γ— 10 βˆ’ 5 , f L = 0.92 1 βˆ’ 0.025 + 0.024 βˆ’ 0.015 + 0.017 , S = βˆ’ 0.26 Β± 0.19 Β± 0.08 , and C = βˆ’ 0.02 Β± 0.1 2 βˆ’ 0.05 + 0.06 , where the first uncertainties are statistical and the second are systematic. We use these results to perform an isospin analysis to constrain the Cabibbo-Kobayashi-Maskawa angle Ο• 2 and obtain two solutions; the result consistent with other Standard Model constraints is Ο• 2 = ( 92.6 βˆ’ 4.7 + 4.5 ) Β° . Published by the American Physical Society 2025

Adachi, I. (ORCID:0000000322870173)β†—
DOE OSTI2025

Measurement of branching fractions, C P asymmetry, and isospin asymmetry for B β†’ ρ Ξ³ decays using Belle and Belle II data

We present measurements of B + β†’ ρ + Ξ³ and B 0 β†’ ρ 0 Ξ³ decays using a combined data sample of 772 Γ— 10 6 B B Β― pairs collected by the Belle experiment and 387 Γ— 10 6 B B Β― pairs collected by the Belle II experiment in e + e βˆ’ collisions at the Ο’ ( 4 S ) resonance. After an optimized selection, a simultaneous fit to the Belle and Belle II datasets yields 114 Β± 12 B + β†’ ρ + Ξ³ and 99 Β± 12 B 0 β†’ ρ 0 Ξ³ decays. The measured branching fractions are ( 13.1 βˆ’ 1.9 βˆ’ 1.2 + 2.0 + 1.3 ) Γ— 10 βˆ’ 7 and ( 7.6 Β± 1.3 βˆ’ 0.8 + 1.0 ) Γ— 10 βˆ’ 7 for B + β†’ ρ + Ξ³ and B 0 β†’ ρ 0 Ξ³ decays, respectively, where the first uncertainty is statistical and the second is systematic. We also measure the isospin asymmetry A I ( B β†’ ρ Ξ³ ) = ( 10.9 βˆ’ 11.7 βˆ’ 7.3 + 11.2 + 7.8 ) % and the direct C P asymmetry A C P ( B + β†’ ρ + Ξ³ ) = ( βˆ’ 8.2 Β± 15.2 βˆ’ 1.3 + 2.0 ) % . Published by the American Physical Society 2025

Adachi, I. (ORCID:0000000322870173)β†—
DOE OSTI2025

Measurement of the time-integrated C P asymmetry in D 0 β†’ K S 0 K S 0 decays using Belle and Belle II data

We measure the time-integrated C P asymmetry in D 0 β†’ K S 0 K S 0 decays reconstructed in e + e βˆ’ β†’ c c Β― events collected by the Belle and Belle II experiments. The corresponding data samples have integrated luminosities of 980 and 428 fb βˆ’ 1 , respectively. The D 0 decays are required to originate from the D * + β†’ D 0 Ο€ + decay, which determines the charm flavor at production time. A control sample of D 0 β†’ K + K βˆ’ decays is used to correct for production and detection asymmetries. The result, ( βˆ’ 1.4 Β± 1.3 ( stat ) Β± 0.1 ( syst ) ) % , is consistent with previous determinations and with C P symmetry. Published by the American Physical Society 2025

Adachi, I. (ORCID:0000000322870173)β†—
DOE OSTI2025

Observation of time-dependent C P violation and measurement of the branching fraction of B 0 β†’ J / ψ Ο€ 0 decays

We present a measurement of the branching fraction and time-dependent charge-parity ( C P ) decay-rate asymmetries in B 0 β†’ J / ψ Ο€ 0 decays. The data sample was collected with the Belle II detector at the SuperKEKB asymmetric e + e βˆ’ collider in 2019–2022 and contains ( 387 Β± 6 ) Γ— 10 6 B B Β― meson pairs from Ο’ ( 4 S ) decays. We reconstruct 392 Β± 24 signal decays and fit the C P parameters from the distribution of the proper-decay-time difference of the two B mesons. We measure the branching fraction to be ( B 0 β†’ J / ψ Ο€ 0 ) = ( 2.00 Β± 0.12 Β± 0.09 ) Γ— 10 βˆ’ 5 and the direct and mixing-induced C P asymmetries to be C C P = 0.13 Β± 0.12 Β± 0.03 and S C P = βˆ’ 0.88 Β± 0.17 Β± 0.03 , respectively, where the first uncertainties are statistical and the second are systematic. We observe mixing-induced C P violation with a significance of 5.0 standard deviations for the first time in this mode. Published by the American Physical Society 2025

Adachi, I. (ORCID:0000000322870173)β†—
DOE OSTI2024

Measurement of the e + e βˆ’ β†’ Ο€ + Ο€ βˆ’ Ο€ 0 cross section in the energy range 0.62–3.50 GeV at Belle II

We report a measurement of the e + e βˆ’ β†’ Ο€ + Ο€ βˆ’ Ο€ 0 cross section in the energy range from 0.62 to 3.50 GeV using an initial-state radiation technique. We use an e + e βˆ’ data sample corresponding to 191 fb βˆ’ 1 of integrated luminosity, collected at a center-of-mass energy at or near the Ο’ ( 4 S ) resonance with the Belle II detector at the SuperKEKB collider. Signal yields are extracted by fitting the two-photon mass distribution in e + e βˆ’ β†’ Ο€ + Ο€ βˆ’ Ο€ 0 Ξ³ events, which involve a Ο€ 0 β†’ Ξ³ Ξ³ decay and an energetic photon radiated from the initial state. Signal efficiency corrections with an accuracy of 1.6% are obtained from several control data samples. The uncertainty on the cross section at the Ο‰ and Ο• resonances is dominated by the systematic uncertainty of 2.2%. The resulting cross sections in the 0.62–1.80 GeV energy range yield a ΞΌ 3 Ο€ = [ 48.91 Β± 0.23 ( stat ) Β± 1.07 ( syst ) ] Γ— 10 βˆ’ 10 for the leading-order hadronic vacuum polarization contribution to the muon anomalous magnetic moment. This result differs by 2.5 standard deviations from the most precise current determination. Published by the American Physical Society 2024

Adachi, I. (ORCID:0000000322870173)β†—
DOE OSTI2024

Search for the baryon number and lepton number violating decays Ο„ βˆ’ β†’ Ξ› Ο€ βˆ’ and Ο„ βˆ’ β†’ Ξ› Β― Ο€ βˆ’ at Belle II

We present a search for the baryon number B and lepton number L violating decays Ο„ βˆ’ β†’ Ξ› Ο€ βˆ’ and Ο„ βˆ’ β†’ Ξ› Β― Ο€ βˆ’ produced from the e + e βˆ’ β†’ Ο„ + Ο„ βˆ’ process, using a 364 fb βˆ’ 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 | Ξ” ( B βˆ’ L ) | equal to 2 and 0, respectively. Upper limits at 90% credibility level on the branching fractions of Ο„ βˆ’ β†’ Ξ› Ο€ βˆ’ and Ο„ βˆ’ β†’ Ξ› Β― Ο€ βˆ’ are determined to be 4.7 Γ— 10 βˆ’ 8 and 4.3 Γ— 10 βˆ’ 8 , respectively. Published by the American Physical Society 2024

Adachi, I. (ORCID:0000000322870173)β†—