Engineering topics

Bae, H. (ORCID:0000000313938631)

Publications and source records attributed to Bae, H. (ORCID:0000000313938631).

At least 19 records

DOE OSTI2025

Search for the lepton-flavor-violating τ − → e ∓ ℓ ± ℓ − decays at Belle II

We present the result of a search for the charged-lepton-flavor violating decays τ − → e ∓ ℓ ± ℓ − , where ℓ is a muon or an electron, using a data sample with an integrated luminosity of 428 fb −1 recorded by the Belle II experiment at the SuperKEKB e + e − collider. The selection of e + e − → τ + τ − events containing a signal candidate is based on an inclusive-tagging reconstruction and on a boosted decision tree to suppress background. Upper limits on the branching fractions between 1.3 and 2.5 × 10 −8 are set at the 90% confidence level. These results are the most stringent bounds to date for four of the modes.

flavour physics↗

DOE OSTI2025

Search for an axion-like particle in B → K (*) a(→ γγ) decays at Belle

We report a search for an axion-like particle a in B → 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 −1 data sample collected at the Υ(4S) resonance energy, corresponding to a sample of 772 × 10 6 Υ(4S) events. In this study, we search for the decay of the axion-like particle into a pair of photons, a → γγ. 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 × 10 −6 GeV −1 to 3 × 10 −5 GeV −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 𝐵 + → 𝐾 + ⁢$𝑣\bar{𝑣}$ measurement at Belle II

We recently measured the branching fraction of the 𝐵 + → 𝐾 + ⁢$𝑣\bar{𝑣}$ decay using 362 fb −1 of on-resonance 𝑒 + ⁢𝑒 − 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 |𝐶 VL +𝐶 VR |, |𝐶 SL +𝐶 SR |, and |𝐶 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)↗

DOE OSTI2025

Measurement of the 𝐷 0 →𝐾 − ⁢𝜋 + ⁢𝑒 + ⁢𝑒 − branching fraction and search for 𝐷 0 → 𝜋 + ⁢𝜋 − ⁢𝑒 + ⁢𝑒 − and 𝐷 0 →𝐾 + ⁢𝐾 − ⁢𝑒 + ⁢𝑒 − decays at Belle

We present a study of the rare charm meson decays 𝐷 0 →𝐾 + ⁢𝐾 − ⁢𝑒 + ⁢𝑒 − , 𝜋 + ⁢𝜋 − ⁢𝑒 + ⁢𝑒 − , and 𝐾 − ⁢𝜋 + ⁢𝑒 + ⁢𝑒 − using a 942 fb −1 dataset collected by the Belle detector at the KEKB asymmetric-energy 𝑒 + ⁢𝑒 − collider. We identify 𝐷 0 candidates via the charge of the pion from 𝐷* + →𝐷 0 ⁢𝜋 + decays and normalize the branching fractions to 𝐷 0 → 𝐾 − ⁢𝜋 + ⁢𝜋 − ⁢𝜋 + decays. The branching fraction for decay 𝐷 0 → 𝐾 − ⁢𝜋 + ⁢𝑒 + ⁢𝑒 − is measured to be (39.6 ± 4.5 (stat) ± 2.9 (syst)) × 10 −7 , with the dielectron mass in the 𝜌/𝜔 mass region 675 < 𝑚 𝑒⁢𝑒 < 875 MeV/⁢𝑐 2 . We also search for 𝐷 0 → ℎ − ⁡ℎ (′)+ ⁡𝑒 + ⁢𝑒 − (ℎ (′) = 𝐾, 𝜋) decays with the dielectron mass near the 𝜂 and 𝜙 resonances, and away from these resonances for the 𝐾 + ⁢𝐾 − ⁢𝑒 + ⁢𝑒 − and 𝜋 + ⁢𝜋 − ⁢𝑒 + ⁢𝑒 − modes. For these modes, we find no significant signals and set 90% confidence level upper limits on their branching fractions at the 𝒪⁡(10 −7 ) level.

branching fraction↗

DOE OSTI2025

Search for B 0 → K *0 𝜏 + ⁢𝜏 − Decays at the Belle II Experiment

We present a search for the rare flavor-changing neutral-current decay 𝐵 0 →𝐾 *0 ⁢𝜏 + ⁢𝜏 − with data collected by the Belle II experiment at the SuperKEKB electron-positron collider. The analysis uses a 365 fb −1 data sample recorded at the center-of-mass energy of the ϒ⁡(4⁢𝑆) resonance. One of the 𝐵 mesons produced in the ϒ⁡(4⁢𝑆)→𝐵 0 $⁢\overline{𝐵}$ 0 process is fully reconstructed in a hadronic decay mode, while its companion 𝐵 meson is required to decay into a 𝐾 *0 and two 𝜏 leptons of opposite charge. The 𝜏 leptons are reconstructed in final states with a single electron, muon, charged pion or charged 𝜌 meson, and additional neutrinos. We set an upper limit on the branching fraction of ℬ⁡(𝐵 0 →𝐾 *0 ⁢𝜏 + ⁢𝜏 − )<1.8×10 −3 at the 90% confidence level, which is the most stringent constraint reported to date.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2025

Observation of the decays 𝐵 + → Σ 𝑐 ⁢(2455) ++ $\bar{Ξ}^-_c$ and 𝐵 0 → Σ 𝑐 ⁢(2455) 0⁢ $\bar{Ξ}^0_𝑐$

We report the first observation of the two-body baryonic decays 𝐵 + → Σ 𝑐 ⁢(2455) ++ $\bar{Ξ}^-_c$ and 𝐵 0 → Σ 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⁡(𝐵 + → Σ 𝑐 ⁢(2455) ++ $\bar{Ξ}^-_c$) = (5.74 ± 1.11 ± 0.4⁢2$^{+2.47}_{−1.53}$) ×10 −4 and ℬ⁡(𝐵 0 → Σ 𝑐 ⁢(2455) 0⁢ $\bar{Ξ}^0_𝑐$) = (4.83 ± 1.12 ± 0.3⁢7$^{+0.72}_{−0.60}$) ×10 −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 −1 and 365 fb −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 − colliders, respectively.

branching fraction↗

DOE OSTI2025

Test of lepton flavor universality with measurements of 𝑅⁡(𝐷 + ) and 𝑅⁡(𝐷* + ) using semileptonic 𝐵 tagging at the Belle II experiment

We report measurements of the ratios of branching fractions ℛ⁡(𝐷 (*)+ ) = ℬ⁡($\bar{𝐵}$ 0 → 𝐷 (*)+ ⁢𝜏 −⁢ $\bar{𝜈}$ 𝜏 )/ℬ⁡($\bar{𝐵}$ 0 → 𝐷 (*)+ ⁢ℓ − $\bar{𝜈}$ ℓ ), where ℓ denotes either an electron or a muon. These ratios test the universality of the charged-current weak interaction. The results are based on a 365 fb −1 data sample collected with the Belle II detector at the SuperKEKB 𝑒 + ⁢𝑒 − collider, which operates at a center-of-mass energy corresponding to the ϒ⁡(4⁢𝑆) resonance, just above the threshold for $𝐵\bar{𝐵}$ production. Signal candidates are reconstructed by selecting events in which the companion 𝐵 meson from the ϒ⁡(4⁢𝑆) → $𝐵\bar{𝐵}$ decay is identified in semileptonic modes. The 𝜏 lepton is reconstructed via its leptonic decays. We obtain ℛ⁡(𝐷 + ) = 0.418$^{+0.075}_{−0.073}$⁢(stat)$^{+0.049}_{−0.056}$⁢(syst) and ℛ⁡(𝐷 *+ ) = 0.306$^{+0.035}_{−0.033}$⁢(stat)$^{+0.016}_{−0.018⁢}$(syst), which are consistent with world average values. Accounting for the correlation between them, these values differ from the Standard Model expectation by a collective significance of 1.7 standard deviations.

bottom quark↗

DOE OSTI2025

Search for lepton flavor-violating decay modes B 0 → K* 0 τ ± ℓ ∓ (ℓ = e, μ) 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 → K *0 τ ± ℓ ∓ , where ℓ ∓ is either an electron or a muon. The results are based on 365 fb −1 and 711 fb −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 → K* 0 τ ± ℓ ∓ decays and set upper limits on the branching fractions in the range of (2.9–6.4)×10 −5 at 90% confidence level.

B physics↗

DOE OSTI2025

Measurement of the 𝐶⁢𝑃 asymmetry in 𝐷 + → 𝜋 + ⁢𝜋 0 decays at Belle II

We measure the 𝐶⁢𝑃 asymmetry in 𝐷 + → 𝜋 + ⁢𝜋 0 decays reconstructed in 𝑒 + ⁢𝑒 − collisions at the Belle II experiment using a dataset corresponding to an integrated luminosity of 428 fb −1 . A control sample of 𝐷 + → 𝜋 + ⁢𝐾$^0_𝑆$ decays is used to correct for detection and production asymmetries. The result 𝐴 𝐶⁢𝑃 ⁡(𝐷 + → 𝜋 + ⁢𝜋 0 ) = (−1.8 ± 0.9 ± 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 𝐶⁢𝑃 symmetry from the standard model and with results of previous measurements.

CP violation↗

DOE OSTI2025

Search for Lepton-Flavor-Violating Decay Modes 𝐵 0 →𝐾$^0_𝑆$⁢𝜏 ± ⁢ℓ ∓ with Hadronic 𝐵 Tagging at Belle and Belle II

We present the first search for the lepton-flavor-violating decay modes 𝐵 0 →𝐾$^0_𝑆$⁢𝜏 ± ⁢ℓ ∓ (ℓ=𝜇,𝑒) using the 711 and 365 fb −1 data samples recorded by the Belle and Belle II detectors, respectively. We use a hadronic 𝐵-tagging technique to fully reconstruct a 𝐵 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 𝐵 0 →𝐾$^0_𝑆$⁢𝜏 ± ⁢ℓ ∓ decays and set 90% confidence level upper limits on the branching fractions in the range of [0.8,3.6] ×10 −5 .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2025

Measurement of the time-integrated 𝐶⁢𝑃 asymmetry in 𝐷 0 → 𝐾$^{0}_{S}$𝐾$^{0}_{S}$ decays using opposite-side flavor tagging at Belle and Belle II

We measure the time-integrated 𝐶⁢𝑃 asymmetry in 𝐷 0 → 𝐾$^{0}_{S}$𝐾$^{0}_{S}$ decays reconstructed in 𝑒 + ⁢𝑒 − → $c\bar{c}$ events collected by the Belle and Belle II experiments. The corresponding data samples have integrated luminosities of 980 and 428 fb −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 − → $c\bar{c}$ event. This results in a sample which is independent from any other previously used at Belle or Belle II. The result, 𝐴 𝐶⁢𝑃 ⁡(𝐷 0 → 𝐾$^{0}_{S}$𝐾$^{0}_{S}$)=(1.3±2.0±0.2)%, where the first uncertainty is statistical and the second systematic, is consistent with previous determinations and with 𝐶⁢𝑃 symmetry.

CP violation↗

DOE OSTI2025

Search for 𝑃 𝑐$\overline{𝑐}$𝑠 ⁢(4459) 0 and 𝑃 𝑐$\overline{𝑐}$𝑠 (4338) 0 in ϒ(1𝑆,2𝑆) Inclusive Decays at Belle

Using data samples of 102 million ϒ⁡(1⁢𝑆) events and 158 million ϒ⁡(2⁢𝑆) events collected by the Belle detector at the KEKB asymmetric-energy 𝑒+⁢𝑒− collider, we search for [𝑢⁢𝑑⁢𝑠⁢𝑐$\overline{𝑐}$ ] pentaquark states decaying to 𝐽/𝜓⁢Λ. Using the first observations of ϒ⁡(1⁢𝑆,2⁢𝑆) inclusive decays to 𝐽/𝜓⁢Λ, we find evidence of the 𝑃 𝑐$\overline{𝑐}$𝑠 ⁢(4459) 0 state with a local significance of 3.3 standard deviations, including statistical and systematic uncertainties. We measure the mass and width of the 𝑃 𝑐$\overline{𝑐}$𝑠 ⁢(4459) 0 to be (4471.7±4.8±0.6) MeV/𝑐 2 and (22 ±13 ±3) MeV, respectively. The branching fractions for 𝑃 𝑐$\overline{𝑐}$𝑠 ⁢(4459) 0 production are measured to be ℬ⁡[ϒ⁡(1⁢𝑆)→𝑃 𝑐$\overline{𝑐}$𝑠 ⁢(4459)0/ $\overline{𝑃}$ 𝑐$\overline{𝑐}$𝑠 ⁢(4459) 0 +anything]=(3.5±2.0±0.2)×10 −6 and ℬ⁡[ϒ⁡(2⁢𝑆)→𝑃 𝑐$\overline{𝑐}$𝑠 ⁢(4459) 0 /$\overline{𝑃}$ 𝑐$\overline{𝑐}$𝑠 ⁢(4459) 0 +anything]=(2.9±1.7±0.4)×10 −6 . The inclusive branching fractions of ϒ⁡(1⁢𝑆,2⁢𝑆) →𝐽/𝜓⁢Λ/$\overline{Λ}$ are measured to be ℬ⁡[ϒ⁡(1⁢𝑆) →𝐽/𝜓⁢Λ/$\overline{Λ}$ +anything] =(36.9 ±5.3 ±2.4) ×10 −6 and ℬ⁡[ϒ⁡(2⁢𝑆) →𝐽/𝜓⁢Λ/$\overline{Λ}$ +anything] =(22.3 ±5.7 ±3.1) ×10 −6 . We measure the visible cross section 𝜎⁡(𝑒+⁢𝑒−→𝐽/𝜓⁢Λ/ $\overline{Λ}$ +anything)=(90±14±6) fb for the continuum production at √𝑠 =10.52 GeV. In all cases, the first uncertainties are statistical and the second are systematic.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2025

Measurement of the branching fraction of Λ + 𝑐 →𝑝⁢𝐾 0 𝑆⁢ 𝜋 0 at Belle

We report a precise measurement of the ratio of branching fractions ℬ⁡(Λ$^+_𝑐$ → 𝑝⁢𝐾$^0_𝑆$⁢𝜋 0 )/ℬ⁡(Λ$^+_𝑐$ → 𝑝⁢𝐾 − ⁢𝜋 + ) using 980 fb −1 of 𝑒 + ⁢𝑒 − data from the Belle experiment. We obtain a value of ℬ⁡(Λ$^+_𝑐$ → 𝑝⁢𝐾$^0_𝑆$⁢𝜋 0 )/ℬ⁡(Λ$^+_𝑐$ → 𝑝⁢𝐾 − ⁢𝜋 + ) =0.339 ±0.002 ±0.009, where the first and second uncertainties are statistical and systematic, respectively. This Belle result is consistent with the previous measurement from the CLEO experiment but has a fivefold improvement in precision. By combining our result with the world average ℬ⁡(Λ$^+_𝑐$ → 𝑝⁢𝐾 − ⁢𝜋 + ), we obtain the absolute branching fraction ℬ⁡(Λ$^+_𝑐$ → 𝑝⁢𝐾$^0_𝑆$⁢𝜋 0 ) =(2.12 ± 0.01 ±0.05 ±0.10)%, where the uncertainties are statistical, systematic, and the uncertainty in the absolute branching fraction scale ℬ⁡(Λ$^+_𝑐$ → 𝑝⁢𝐾 − ⁢𝜋 + ), respectively. This measurement can shed light on hadronic decay mechanisms in charmed baryon decays.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2025

Measurement of the time-integrated 𝐶⁢𝑃 asymmetry in 𝐷 0 → 𝜋 0 ⁢𝜋 0 decays at Belle II

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

CP violation↗

DOE OSTI2025

Measurement of branching fractions, C P asymmetry, and isospin asymmetry for B → ρ γ decays using Belle and Belle II data

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

Adachi, I. (ORCID:0000000322870173)↗

DOE OSTI2025

Observation of time-dependent C P violation and measurement of the branching fraction of B 0 → J / ψ π 0 decays

We present a measurement of the branching fraction and time-dependent charge-parity ( C P ) decay-rate asymmetries in B 0 → J / ψ π 0 decays. The data sample was collected with the Belle II detector at the SuperKEKB asymmetric e + e − collider in 2019–2022 and contains ( 387 ± 6 ) × 10 6 B B ¯ meson pairs from ϒ ( 4 S ) decays. We reconstruct 392 ± 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 → J / ψ π 0 ) = ( 2.00 ± 0.12 ± 0.09 ) × 10 − 5 and the direct and mixing-induced C P asymmetries to be C C P = 0.13 ± 0.12 ± 0.03 and S C P = − 0.88 ± 0.17 ± 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)↗

DOE OSTI2024

Measurement of the e + e − → π + π − π 0 cross section in the energy range 0.62–3.50 GeV at Belle II

We report a measurement of the e + e − → π + π − π 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 − data sample corresponding to 191 fb − 1 of integrated luminosity, collected at a center-of-mass energy at or near the ϒ ( 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 − → π + π − π 0 γ events, which involve a π 0 → γ γ 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 ω and ϕ 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 μ 3 π = [ 48.91 ± 0.23 ( stat ) ± 1.07 ( syst ) ] × 10 − 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)↗