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Eppelt, J. (ORCID:0000000183683721)

Publications and source records attributed to Eppelt, J. (ORCID:0000000183683721).

15 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

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

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

Search for a Dark Higgs Boson Produced in Association with Inelastic Dark Matter at the Belle II Experiment

Inelastic dark matter models that have two dark matter particles and a massive dark photon can reproduce the observed relic dark matter density without violating cosmological limits. The mass splitting between the two dark matter particles πœ’ 1 and πœ’ 2 , with π‘šβ‘(πœ’ 2 ) >π‘šβ‘(πœ’ 1 ), is induced by a dark Higgs field and a corresponding dark Higgs boson β„Žβ€². We present a search for dark matter in events with two vertices, at least one of which must be displaced from the interaction region, and missing energy. Using a 365 fb βˆ’1 data sample collected at Belle II, which operates at the SuperKEKB 𝑒 + ⁒𝑒 βˆ’ collider, we observe no evidence for a signal. We set upper limits on the product of the production cross section 𝜎⁑(𝑒 + ⁒𝑒 βˆ’ β†’ β„Žβ€²β‘πœ’ 1 β’πœ’ 2 ), and the product of branching fractions ℬ⁑(πœ’ 2 β†’ πœ’ 1⁒ 𝑒 + ⁒𝑒 βˆ’ ) ×ℬ⁑(β„Žβ€² β†’ π‘₯ + ⁒π‘₯ βˆ’ ), where π‘₯ + ⁒π‘₯ βˆ’ indicates πœ‡ + β’πœ‡ βˆ’ , πœ‹ + β’πœ‹ βˆ’ , or 𝐾 + ⁒𝐾 βˆ’ , as functions of β„Žβ€² mass and lifetime at the level of 10 βˆ’1 fb. We set model-dependent upper limits on the dark Higgs mixing angle at the level of 10 βˆ’5 and on the dark photon kinetic mixing parameter at the level of 10 βˆ’3 . This is the first search for dark Higgs bosons in association with inelastic dark matter.

dark matter↗
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 ${\tau }^{-}\to {{\ell}}^{-}{K}_{s}^{0}$ 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

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

Search for 𝑃 𝑐$\overline{𝑐}$𝑠 ⁒(4459) 0 and 𝑃 𝑐$\overline{𝑐}$𝑠 (4338) 0 in Ο’(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+β’π‘’βˆ’ collider, we search for [𝑒⁒𝑑⁒𝑠⁒𝑐$\overline{𝑐}$ ] pentaquark states decaying to 𝐽/πœ“β’Ξ›. Using the first observations of ϒ⁑(1⁒𝑆,2⁒𝑆) inclusive decays to 𝐽/πœ“β’Ξ›, 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 (4471.7Β±4.8Β±0.6) MeV/𝑐 2 and (22 Β±13 Β±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]=(3.5Β±2.0Β±0.2)Γ—10 βˆ’6 and ℬ⁑[ϒ⁑(2⁒𝑆)→𝑃 𝑐$\overline{𝑐}$𝑠 ⁒(4459) 0 /$\overline{𝑃}$ 𝑐$\overline{𝑐}$𝑠 ⁒(4459) 0 +anything]=(2.9Β±1.7Β±0.4)Γ—10 βˆ’6 . The inclusive branching fractions of ϒ⁑(1⁒𝑆,2⁒𝑆) →𝐽/πœ“β’Ξ›/$\overline{Ξ›}$ are measured to be ℬ⁑[ϒ⁑(1⁒𝑆) →𝐽/πœ“β’Ξ›/$\overline{Ξ›}$ +anything] =(36.9 Β±5.3 Β±2.4) Γ—10 βˆ’6 and ℬ⁑[ϒ⁑(2⁒𝑆) →𝐽/πœ“β’Ξ›/$\overline{Ξ›}$ +anything] =(22.3 Β±5.7 Β±3.1) Γ—10 βˆ’6 . We measure the visible cross section 𝜎⁑(𝑒+β’π‘’βˆ’β†’π½/πœ“β’Ξ›/ $\overline{Ξ›}$ +anything)=(90Β±14Β±6) fb for the continuum production at βˆšπ‘  =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 Ξ› + 𝑐 →𝑝⁒𝐾 0 𝑆⁒ πœ‹ 0 at Belle

We report a precise measurement of the ratio of branching fractions ℬ⁑(Ξ›$^+_𝑐$ β†’ 𝑝⁒𝐾$^0_𝑆$β’πœ‹ 0 )/ℬ⁑(Ξ›$^+_𝑐$ β†’ 𝑝⁒𝐾 βˆ’ β’πœ‹ + ) using 980 fb βˆ’1 of 𝑒 + ⁒𝑒 βˆ’ data from the Belle experiment. We obtain a value of ℬ⁑(Ξ›$^+_𝑐$ β†’ 𝑝⁒𝐾$^0_𝑆$β’πœ‹ 0 )/ℬ⁑(Ξ›$^+_𝑐$ β†’ 𝑝⁒𝐾 βˆ’ β’πœ‹ + ) =0.339 Β±0.002 Β±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⁑(Ξ›$^+_𝑐$ β†’ 𝑝⁒𝐾 βˆ’ β’πœ‹ + ), we obtain the absolute branching fraction ℬ⁑(Ξ›$^+_𝑐$ β†’ 𝑝⁒𝐾$^0_𝑆$β’πœ‹ 0 ) =(2.12 Β± 0.01 Β±0.05 Β±0.10)%, where the uncertainties are statistical, systematic, and the uncertainty in the absolute branching fraction scale ℬ⁑(Ξ›$^+_𝑐$ β†’ 𝑝⁒𝐾 βˆ’ β’πœ‹ + ), 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 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 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 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†—
DOE OSTI2023

Photon Reconstruction in the Belle II Calorimeter Using Graph Neural Networks

We present the study of a fuzzy clustering algorithm for the Belle II electromagnetic calorimeter using Graph Neural Networks. We use a realistic detector simulation including simulated beam backgrounds and focus on the reconstruction of both isolated and overlapping photons. We find significant improvements of the energy resolution compared to the currently used reconstruction algorithm for both isolated and overlapping photons of more than 30% for photons with energies E Ξ³ < 0.5 GeV and high levels of beam backgrounds. Overall, the GNN reconstruction improves the resolution and reduces the tails of the reconstructed energy distribution and therefore is a promising option for the upcoming high luminosity running of Belle II.

Calorimeter↗