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Frey, A. (ORCID:0000000174703874)

Publications and source records attributed to Frey, A. (ORCID:0000000174703874).

At least 19 records
All sourcesNASA NTRSDOE OSTI
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

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 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 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 OSTI2024

New graph-neural-network flavor tagger for Belle II and measurement of sin 2β’πœ™ 1 in 𝐡 0 β†’ 𝐽/πœ“β’πΎ$^0_ S$ decays

We present GFlaT, a new algorithm that uses a graph-neural-network to determine the flavor of neutral 𝐡 mesons produced in ϒ⁑(4⁒𝑆) decays. It improves previous algorithms by using the information from all charged final-state particles and the relations between them. We evaluate its performance using 𝐡 decays to flavor-specific hadronic final states reconstructed in a 362 fb βˆ’1 sample of electron-positron collisions collected at the ϒ⁑(4⁒𝑆) resonance with the Belle II detector at the SuperKEKB collider. We achieve an effective tagging efficiency of (37.40 Β± 0.43 Β± 0.36%), where the first uncertainty is statistical and the second systematic, which is 18% better than the previous Belle II algorithm. Demonstrating the algorithm, we use 𝐡 0 →𝐽/πœ“β’πΎ$^0_ S$ decays to measure the mixing-induced and direct 𝐢⁒𝑃 violation parameters, 𝑆 = (0.724 Β± 0.035 Β± 0.009) and 𝐢 = (βˆ’0.035 Β± 0.026 Β± 0.029).

CP violation↗
DOE OSTI2024

Study of Ξ₯(10753) decays to Ο€+Ο€βˆ’Ξ₯(nS) final states at Belle II

Abstract We present an analysis of the processe + e βˆ’ β†’Ο€ + Ο€ βˆ’ Ξ₯(nS) (wheren= 1, 2, or 3) reconstructed in 19.6 fb βˆ’1 of Belle II data during a special run of the SuperKEKB collider at four energy points near the peak of the Ξ₯(10753) resonance. By analyzing the mass distribution of theΟ€ + Ο€ βˆ’ Ξ₯(nS) system and the Born cross sections of thee + e βˆ’ β†’Ο€ + Ο€ βˆ’ Ξ₯(nS) process, we report the first observation of Ξ₯(10753) decays to theΟ€ + Ο€ βˆ’ Ξ₯(1S) andΟ€ + Ο€ βˆ’ Ξ₯(2S) final states, and find no evidence for decays toΟ€ + Ο€ βˆ’ Ξ₯(3S). Possible intermediate states in theΟ€ + Ο€ βˆ’ Ξ₯(1S,2S) transitions are also investigated, and no evidence for decays proceeding via the$$ {\pi}^{\mp }{Z}_b^{\pm } $$ Ο€ βˆ“ Z b Β± orf 0 (980)Ξ₯(nS) intermediate states is found. We measure Born cross sections for thee + e βˆ’ β†’Ο€ + Ο€ βˆ’ Ξ₯(nS) process that, combined with results from Belle, obtain the mass and width of Ξ₯(10753) to be (10756.6 Β± 2.7 Β± 0.9) MeV/c 2 and (29.0 Β± 8.8 Β± 1.2) MeV, respectively. The relative ratios of the Born cross sections at the Ξ₯(10753) resonance peak are also reported for the first time.

Physics↗
DOE OSTI2024

Measurement of the branching fraction of the decay B βˆ’ β†’ D 0 ρ ( 770 ) βˆ’ at Belle II

We measure the branching fraction of the decay B βˆ’ β†’ D 0 ρ ( 770 ) βˆ’ using data collected with the Belle II detector. The data contain 387 million B B Β― pairs produced in e + e βˆ’ collisions at the Ο’ ( 4 S ) resonance. We reconstruct 8360 Β± 180 decays from an analysis of the distributions of the B βˆ’ energy and the ρ ( 770 ) βˆ’ helicity angle. We determine the branching fraction to be ( 0.939 Β± 0.021 ( stat ) Β± 0.050 ( syst ) ) % , in agreement with previous results. Our measurement improves the relative precision of the world average by more than a factor of two. Published by the American Physical Society 2024

Astronomy & Astrophysics↗
DOE OSTI2024

Search for a ΞΌ + ΞΌ βˆ’ resonance in four-muon final states at Belle II

We report on a search for a resonance X decaying to a pair of muons in e + e βˆ’ β†’ ΞΌ + ΞΌ βˆ’ X events in the 0.212 – 9.000 GeV / c 2 mass range, using 178 fb βˆ’ 1 of data collected by the Belle II experiment at the SuperKEKB collider at a center of mass energy of 10.58 GeV. The analysis probes two different models of X beyond the standard model: a Z β€² vector boson in the L ΞΌ βˆ’ L Ο„ model and a muonphilic scalar. We observe no evidence for a signal and set exclusion limits at the 90% confidence level on the products of cross section and branching fraction for these processes, ranging from 0.046 fb to 0.97 fb for the L ΞΌ βˆ’ L Ο„ model and from 0.055 fb to 1.3 fb for the muonphilic scalar model. For masses below 6 GeV / c 2 , the corresponding constraints on the couplings of these processes to the standard model range from 0.0008 to 0.039 for the L ΞΌ βˆ’ L Ο„ model and from 0.0018 to 0.040 for the muonphilic scalar model. These are the first constraints on the muonphilic scalar from a dedicated search. Published by the American Physical Society 2024

Astronomy & Astrophysics↗
DOE OSTI2024

First Measurement of R ( X Ο„ / β„“ ) as an Inclusive Test of the b β†’ c Ο„ Ξ½ Anomaly

We measure the tau-to-light-lepton ratio of inclusive B -meson branching fractions R ( X Ο„ / β„“ ) ≑ B ( B β†’ X Ο„ Ξ½ ) / B ( B β†’ X β„“ Ξ½ ) , where β„“ indicates an electron or muon, and thereby test the universality of charged-current weak interactions. We select events that have one fully reconstructed B meson and a charged lepton candidate from 189 fb βˆ’ 1 of electron-positron collision data collected with the Belle II detector. We find R ( X Ο„ / β„“ ) = 0.228 Β± 0.016 ( stat ) Β± 0.036 ( syst ) , in agreement with standard-model expectations. This is the first direct measurement of R ( X Ο„ / β„“ ) . Published by the American Physical Society 2024

Physics↗
DOE OSTI2024

Search for the e + e βˆ’ β†’ Ξ· b ( 1 S ) Ο‰ and e + e βˆ’ β†’ Ο‡ b 0 ( 1 P ) Ο‰ processes at s = 10.745 GeV

We search for the e + e βˆ’ β†’ Ξ· b ( 1 S ) Ο‰ and e + e βˆ’ β†’ Ο‡ b 0 ( 1 P ) Ο‰ processes at a center-of-mass energy of 10.745 GeV, which is close to the peak of the Ο’ ( 10753 ) state. We use data collected by the Belle II experiment during a special run, corresponding to an integrated luminosity of 9.8 fb βˆ’ 1 . We reconstruct Ο‰ β†’ Ο€ + Ο€ βˆ’ Ο€ 0 decays and use the Ο‰ meson’s recoil mass to search for the signals. We do not find evidence for either process, and set upper limits on the corresponding Born-level cross sections of 2.5 pb and 7.8 pb, respectively, at the 90% confidence level. The Ο‡ b 0 ( 1 P ) Ο‰ limit is the result of a combination of this analysis and a previous search using full reconstruction. Published by the American Physical Society 2024

Astronomy & Astrophysics↗
DOE OSTI2023

First Simultaneous Determination of Inclusive and Exclusive | V u b |

The first simultaneous determination of the absolute value of the Cabibbo-Kobayashi-Maskawa matrix element V ub using inclusive and exclusive decays is performed with the full Belle data set at the $Ξ₯$(4S) resonance, corresponding to an integrated luminosity of 711 fb -1 . We analyze collision events in which one B meson is fully reconstructed in hadronic modes. This allows for the reconstruction of the hadronic X u system of the semileptonic b β†’ $Ο€β„“e_β„“$ decay. We separate exclusive B β†’ $Ο€β„“\overline{Ξ½}_β„“$ decays from other inclusive B β†’ $X_uβ„“\overline{Ξ½}_β„“$ and backgrounds with a two-dimensional fit that utilizes the number of charged pions in the X u system and the four-momentum transfer q 2 between the B and X u systems. Combining our measurement with information from lattice QCD and QCD calculations of the inclusive partial rate as well as external experimental information on the shape of the B β†’ $Ο€β„“e_β„“$ form factor, we determine |$V^{excl}_{ub}$| = (3.78 Β± 0.23 Β± 0.16 Β± 0.14) Γ— 10 -3 and |$V^{incl}_{ub}$| = (3.88 Β± 0.20 Β± 0.31 Β± 0.09) x 10 -3 , respectively, with the uncertainties being the statistical error, systematic errors, and theory errors. The ratio of |$V^{excl}_{ub}$|/|$V^{incl}_{ub}$| 0.97 Β± 0.12 is compatible with unity.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Precise Measurement of the D s + Lifetime at Belle II

We measure the lifetime of the $D^+_s$ meson using a data sample of 207 fb -1 collected by the Belle II experiment running at the SuperKEKB asymmetric-energy e + e - collider. The lifetime is determined by fitting the decay-time distribution of a sample of 116 Γ— 10 3 $D^+_s$ β†’ φπ + decays. Our result is Ο„$D^+_s$ = (499.5 Β± 1.7 Β± 0.9) fs, where the first uncertainty is statistical and the second is systematic. This result is significantly more precise than previous measurements.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Test of Light-Lepton Universality in the Rates of Inclusive Semileptonic B-Meson Decays at Belle II

We present the first measurement of the ratio of branching fractions of inclusive semileptonic B -meson decays, R ( X e / ΞΌ ) = B ( B β†’ X e Ξ½ ) / B ( B β†’ X ΞΌ Ξ½ ) , a precision test of electron-muon universality, using data corresponding to 189 fb - 1 from electron-positron collisions collected with the Belle II detector. In events where the partner B meson is fully reconstructed, we use fits to the lepton momentum spectra above 1.3 GeV / c to obtain R ( X e / ΞΌ ) = 1.007 Β± 0.009 ( stat ) Β± 0.019 ( syst ) , which is the most precise lepton-universality test of its kind and agrees with the standard-model expectation.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Measured and projected beam backgrounds in the Belle II experiment at the SuperKEKB collider

The Belle II experiment at the SuperKEKB electron–positron collider aims to collect an unprecedented data set of 50 ab -1 to study CP -violation in the B -meson system and to search for Physics beyond the Standard Model. SuperKEKB is already the world’s highest-luminosity collider. In order to collect the planned data set within approximately one decade, the target is to reach a peak luminosity of 6 x 10 35 cm βˆ’2 s βˆ’1 by further increasing the beam currents and reducing the beam size at the interaction point by squeezing the betatron function down to Ξ² $^*_y$ = 0.3 mm. To ensure detector longevity and maintain good reconstruction performance, beam backgrounds must remain well controlled. We report on current background rates in Belle II and compare these against simulation. We find that a number of recent refinements have significantly improved the background simulation accuracy. Finally, we estimate the safety margins going forward. We predict that backgrounds should remain high but acceptable until a luminosity of at least 2.8 x 10 35 cm βˆ’2 s βˆ’1 is reached for Ξ² $^*_y$ = 0.6 mm. At this point, the most vulnerable Belle II detectors, the Time-of-Propagation (TOP) particle identification system and the Central Drift Chamber (CDC), have predicted background hit rates from single-beam and luminosity backgrounds that add up to approximately half of the maximum acceptable rates.

Detector background↗
DOE OSTI2023

First measurement of the Q 2 distribution of X⁑(3915) single-tag two-photon production

We report the first measurement of the Q 2 distribution of X⁑(3915) produced by single-tag two-photon interactions. The decay mode used is X⁑(3915) β†’J/Ψ⁒ω. The covered Q 2 region is from 1.5 (GeV/c) 2 to 10.0 (GeV/c) 2 . We observe 7.9 Β± 3.1⁒(stat) Β± 1.5⁒(syst) events, where we expect 4.1 Β± 0.7 events based on the Q 2 = 0 result from the no-tag two-photon process, extrapolated to higher Q 2 region using the $c\bar{c}$ model of Schuler, Berends, and van Gulik. The shape of the distribution is also consistent with this model; we note that statistical uncertainties are large

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Measurement of differential distributions of B β†’ D*$\ell\bar{v}_{\ell}$ and implications on | V cb |

We present a measurement of the differential shapes of exclusive B β†’ D*$\ell\bar{v}_{\ell}$ (B = B - , $\bar{B}$ 0 and $\ell$ = e, ΞΌ) decays with hadronic tag-side reconstruction for the full 711 fb -1 Belle dataset. We extract the Caprini-Lellouch-Neubert (CLN) and Boyd-Grinstein-Lebed (BGL) form factor parameters and use an external input for the absolute branching fractions to determine the Cabibbo-Kobayashi-Maskawa matrix element and find |V cb | CLN = (40.2 Β± 0.9) x 10 -3 and |V cb | BGL = (40.7 Β± 1.0) x 10 -3 with the zero-recoil lattice QCD point $\mathcal{F}$(1) = 0.906 Β± 0.013. We also perform a study of the impact of beyond zero-recoil lattice QCD calculations on the |V cb | determinations. Additionally, we present the lepton-flavor universality ratio R eΞΌ = $\mathcal{B}$(B β†’ D*e$\bar{v}$ e )/$\mathcal{B}$(B β†’ D*ΞΌ$\bar{v}$ ΞΌ ) = 0.993 Β± 0.023 Β± 0.023, the electron and muon forwardbackward asymmetry and their difference Ξ”A FB = 0.028 Β± 0.028 Β± 0.008, and the electron and muon D* longitudinal polarization fraction and their difference Ξ”F$^{D*}_L$ = 0.030 Β± 0.025 Β± 0.007. The uncertainties quoted correspond to the statistical and systematic uncertainties, respectively.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Novel method for the identification of the production flavor of neutral charmed mesons

We propose a new algorithm for the identification of the production flavor of neutral D mesons in the Belle II experiment. The algorithm exploits the correlation between the flavor of a reconstructed neutral D meson (signal D meson) and the electric charges of particles reconstructed in the rest of the e + e – β†’$c\bar{c}$ event. These include those originating from the decay of the other charm hadron produced in the event, as well as those possibly produced in association with the signal D meson. We develop the algorithm using simulation and calibrate it in data using decay modes that identify the flavor of the decaying neutral D meson. We use a data sample of e + e – collisions, corresponding to 362 fb –1 of integrated luminosity, collected by Belle II at center-of-mass energies near the Ξ₯(4S) mass. The effective tagging efficiency in data is (47.91Β±0.07 (stat) Β±0.51 (syst)) %, independent of the neutral-D-meson decay mode. This charm flavor tagger will approximately double the effective sample size of many CP-violation and charm-mixing measurements that so far have exclusively relied on neutral D mesons originating from D* Β± decays. While developed for Belle II, the basic principles underlying the charm flavor tagger can be used in other experiments, including those at hadron colliders.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗