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Farkas, R. (ORCID:0000000276471429)

Publications and source records attributed to Farkas, R. (ORCID:0000000276471429).

8 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Search for an axion-like particle in B β†’ K (*) a(β†’ Ξ³Ξ³) decays at Belle

We report a search for an axion-like particle a in B β†’ K (*) a decays using data collected with the Belle detector at the KEKB asymmetric-energy electron-positron collider. The search is based on a 711 fb βˆ’1 data sample collected at the Ξ₯(4S) resonance energy, corresponding to a sample of 772 Γ— 10 6 Ξ₯(4S) events. In this study, we search for the decay of the axion-like particle into a pair of photons, a β†’ Ξ³Ξ³. We scan the two-photon invariant mass in the range 0.16 GeV–4.50 GeV for the K modes and 0.16 GeV–4.20 GeV for the K * modes. No significant signal is observed in any of the modes, and 90% confidence level upper limits are established on the coupling to the W boson, g aW , as a function of a mass. The limits range from 3 Γ— 10 βˆ’6 GeV βˆ’1 to 3 Γ— 10 βˆ’5 GeV βˆ’1 , improving the current constraints on g aW by a factor of two over the most stringent previous experimental results.

B physics↗
DOE OSTI2025

Model-agnostic likelihood for the reinterpretation of the 𝐡 + β†’ 𝐾 + ⁒$𝑣\bar{𝑣}$ measurement at Belle II

We recently measured the branching fraction of the 𝐡 + β†’ 𝐾 + ⁒$𝑣\bar{𝑣}$ decay using 362 fb βˆ’1 of on-resonance 𝑒 + ⁒𝑒 βˆ’ collision data under the assumption of Standard Model kinematics, providing the first evidence for this decay. To facilitate future reinterpretations and maximize the scientific impact of this measurement, we publicly release the full analysis likelihood along with all necessary material required for reinterpretation under arbitrary theoretical models sensitive to this measurement. In this work, we demonstrate how the measurement can be reinterpreted within the framework of the weak effective theory. Using a kinematic reweighting technique in combination with the published likelihood, we derive marginal posterior distributions for the Wilson coefficients, construct credible intervals, and assess the goodness of fit to the Belle II data. For the weak effective theory Wilson coefficients, the posterior mode of the magnitudes |𝐢 VL +𝐢 VR |, |𝐢 SL +𝐢 SR |, and |𝐢 TL | corresponds to the point (11.3, 0.0, 8.2). The respective 95% credible intervals are [1.9, 16.2], [0.0, 15.4], and [0.0, 11.2].

bottom quark↗
DOE OSTI2025

Charged-hadron identification at Belle II

The Belle II experiment’s ability to identify particles critically affects the sensitivity of its measurements. We describe Belle II’s algorithms for identifying charged particles and evaluate their performance in separating pions, kaons, and protons using $426\,\text {fb}^{-1}$ of data collected at the energy-asymmetric $e^{+}e^{-}$ collider SuperKEKB in 2019–2022 at center-of-mass energies at and near the mass of the $\Upsilon$ (4S).

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

Observation of the decays 𝐡 + β†’ Ξ£ 𝑐 ⁒(2455) ++ $\bar{Ξ}^-_c$ and 𝐡 0 β†’ Ξ£ 𝑐 ⁒(2455) 0⁒ $\bar{Ξ}^0_𝑐$

We report the first observation of the two-body baryonic decays 𝐡 + β†’ Ξ£ 𝑐 ⁒(2455) ++ $\bar{Ξ}^-_c$ and 𝐡 0 β†’ Ξ£ 𝑐 ⁒(2455) 0⁒ $\bar{Ξ}^0_𝑐$ with significances of 7.3⁒𝜎 and 6.2⁒𝜎, respectively, including statistical and systematic uncertainties. The branching fractions are measured to be ℬ⁑(𝐡 + β†’ Ξ£ 𝑐 ⁒(2455) ++ $\bar{Ξ}^-_c$) = (5.74 Β± 1.11 Β± 0.4⁒2$^{+2.47}_{βˆ’1.53}$) Γ—10 βˆ’4 and ℬ⁑(𝐡 0 β†’ Ξ£ 𝑐 ⁒(2455) 0⁒ $\bar{Ξ}^0_𝑐$) = (4.83 Β± 1.12 Β± 0.3⁒7$^{+0.72}_{βˆ’0.60}$) Γ—10 βˆ’4 . The first and second uncertainties are statistical and systematic, respectively, while the third ones arise from the absolute branching fractions of $\bar{Ξ}^-_c$ or $\bar{Ξ}^0_𝑐$ decays. The data samples used for this analysis have integrated luminosities of 711 fb βˆ’1 and 365 fb βˆ’1 , and were collected at the ϒ⁑(4⁒𝑆) resonance by the Belle and Belle II detectors operating at the KEKB and SuperKEKB asymmetric-energy 𝑒 + ⁒𝑒 βˆ’ colliders, respectively.

branching fraction↗
DOE OSTI2025

Search for lepton flavor-violating decay modes B 0 β†’ K* 0 Ο„ Β± β„“ βˆ“ (β„“ = e, ΞΌ) with hadronic B-tagging at Belle and Belle II

We present the results of a search for the charged-lepton-flavor violating decays B 0 β†’ K *0 Ο„ Β± β„“ βˆ“ , where β„“ βˆ“ is either an electron or a muon. The results are based on 365 fb βˆ’1 and 711 fb βˆ’1 datasets collected with the Belle II and Belle detectors, respectively. We use an exclusive hadronic B-tagging technique, and search for a signal decay in the system recoiling against a fully reconstructed B meson. We find no evidence for B 0 β†’ K* 0 Ο„ Β± β„“ βˆ“ decays and set upper limits on the branching fractions in the range of (2.9–6.4)Γ—10 βˆ’5 at 90% confidence level.

B physics↗
DOE OSTI2025

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

We measure the 𝐢⁒𝑃 asymmetry in 𝐷 + β†’ πœ‹ + β’πœ‹ 0 decays reconstructed in 𝑒 + ⁒𝑒 βˆ’ collisions at the Belle II experiment using a dataset corresponding to an integrated luminosity of 428 fb βˆ’1 . A control sample of 𝐷 + β†’ πœ‹ + ⁒𝐾$^0_𝑆$ decays is used to correct for detection and production asymmetries. The result 𝐴 𝐢⁒𝑃 ⁑(𝐷 + β†’ πœ‹ + β’πœ‹ 0 ) = (βˆ’1.8 Β± 0.9 Β± 0.1)%, where the first uncertainty is statistical and the second systematic, is the most precise determination to date. It agrees with the prediction of 𝐢⁒𝑃 symmetry from the standard model and with results of previous measurements.

CP violation↗
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↗