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Bierwirth, L. (ORCID:0009000301929073)

Publications and source records attributed to Bierwirth, L. (ORCID:0009000301929073).

10 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Measurement of the 𝐷 0 →𝐾 βˆ’ β’πœ‹ + ⁒𝑒 + ⁒𝑒 βˆ’ branching fraction and search for 𝐷 0 β†’ πœ‹ + β’πœ‹ βˆ’ ⁒𝑒 + ⁒𝑒 βˆ’ and 𝐷 0 →𝐾 + ⁒𝐾 βˆ’ ⁒𝑒 + ⁒𝑒 βˆ’ decays at Belle

We present a study of the rare charm meson decays 𝐷 0 →𝐾 + ⁒𝐾 βˆ’ ⁒𝑒 + ⁒𝑒 βˆ’ , πœ‹ + β’πœ‹ βˆ’ ⁒𝑒 + ⁒𝑒 βˆ’ , and 𝐾 βˆ’ β’πœ‹ + ⁒𝑒 + ⁒𝑒 βˆ’ using a 942 fb βˆ’1 dataset collected by the Belle detector at the KEKB asymmetric-energy 𝑒 + ⁒𝑒 βˆ’ collider. We identify 𝐷 0 candidates via the charge of the pion from 𝐷* + →𝐷 0 β’πœ‹ + decays and normalize the branching fractions to 𝐷 0 β†’ 𝐾 βˆ’ β’πœ‹ + β’πœ‹ βˆ’ β’πœ‹ + decays. The branching fraction for decay 𝐷 0 β†’ 𝐾 βˆ’ β’πœ‹ + ⁒𝑒 + ⁒𝑒 βˆ’ is measured to be (39.6 Β± 4.5 (stat) Β± 2.9 (syst)) Γ— 10 βˆ’7 , with the dielectron mass in the 𝜌/πœ” mass region 675 < π‘š 𝑒⁒𝑒 < 875 MeV/⁒𝑐 2 . We also search for 𝐷 0 β†’ β„Ž βˆ’ β‘β„Ž (β€²)+ ⁑𝑒 + ⁒𝑒 βˆ’ (β„Ž (β€²) = 𝐾, πœ‹) decays with the dielectron mass near the πœ‚ and πœ™ resonances, and away from these resonances for the 𝐾 + ⁒𝐾 βˆ’ ⁒𝑒 + ⁒𝑒 βˆ’ and πœ‹ + β’πœ‹ βˆ’ ⁒𝑒 + ⁒𝑒 βˆ’ modes. For these modes, we find no significant signals and set 90% confidence level upper limits on their branching fractions at the π’ͺ⁑(10 βˆ’7 ) level.

branching fraction↗
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

Test of lepton flavor universality with a measurement of R ( D * ) using hadronic B tagging at the Belle II experiment

The ratio of branching fractions R ( D * ) = B ( B Β― β†’ D * Ο„ βˆ’ Ξ½ Β― Ο„ ) / B ( B Β― β†’ D * β„“ βˆ’ Ξ½ Β― β„“ ) , where β„“ is an electron or muon, is measured using a Belle II data sample with an integrated luminosity of 189 fb βˆ’ 1 at the SuperKEKB asymmetric-energy e + e βˆ’ collider. Data is collected at the Ο’ ( 4 S ) resonance, and one B meson in the Ο’ ( 4 S ) β†’ B B Β― decay is fully reconstructed in hadronic decay modes. The accompanying signal B meson is reconstructed as B Β― β†’ D * Ο„ βˆ’ Ξ½ Β― Ο„ using leptonic Ο„ decays. The normalization decay, B Β― β†’ D * β„“ βˆ’ Ξ½ Β― β„“ , produces the same observable final-state particles. The ratio of branching fractions is extracted in a simultaneous fit to two signal-discriminating variables in both channels and yields R ( D * ) = 0.262 βˆ’ 0.039 + 0.041 ( stat ) βˆ’ 0.032 + 0.035 ( syst ) . This result is consistent with the current world average and with Standard Model predictions. Published by the American Physical Society 2024

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

Search for lepton-flavor-violating Ο„ – β†’ ΞΌ – ΞΌ + ΞΌ – decays at Belle II

We present the result of a search for the charged-lepton-flavor violating decay Ο„ – β†’ ΞΌ – ΞΌ + ΞΌ – using a 424 fb –1 sample of data recorded by the Belle II experiment at the SuperKEKB e + e – collider. The selection of e + e – β†’ Ο„ + Ο„ – events is based on an inclusive reconstruction of the non-signal tau decay, and on a boosted decision tree to suppress background. We observe one signal candidate, which is compatible with the expectation from background processes. We set a 90% confidence level upper limit of 1.9 Γ— 10 –8 on the branching fraction of the Ο„ – β†’ ΞΌ – ΞΌ + ΞΌ – decay, which is the most stringent bound to date.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Search for Rare b β†’ d β„“ + β„“ βˆ’ Transitions at Belle

We present the results of a search for the b β†’ d β„“ + β„“ βˆ’ flavor-changing neutral-current rare decays B + , 0 β†’ ( Ξ· , Ο‰ , Ο€ + , 0 , ρ + , 0 ) e + e βˆ’ and B + , 0 β†’ ( Ξ· , Ο‰ , Ο€ 0 , ρ + ) ΞΌ + ΞΌ βˆ’ using a 711 fb βˆ’ 1 data sample that contains 772 Γ— 10 6 B B Β― events. The data were collected at the Ο’ ( 4 S ) resonance with the Belle detector at the KEKB asymmetric-energy e + e βˆ’ collider. We find no evidence for signal and set upper limits on branching fractions at the 90% confidence level in the range ( 3.8 – 47 ) Γ— 10 βˆ’ 8 depending on the decay channel. The obtained limits are the world’s best results. This is the first search for the channels B + , 0 β†’ ( Ο‰ , ρ + , 0 ) e + e βˆ’ and B + , 0 β†’ ( Ο‰ , ρ + ) ΞΌ + ΞΌ βˆ’ . Published by the American Physical Society 2024

Physics↗
DOE OSTI2024

Search for the decay B 0 β†’ Ξ³ Ξ³ using Belle and Belle II data

We report the result of a search for the rare decay B 0 β†’ Ξ³ Ξ³ using a combined dataset of 753 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 from decays of the Ο’ ( 4 S ) resonance produced in e + e βˆ’ collisions. A simultaneous fit to the Belle and Belle II data sets yields 11.0 βˆ’ 5.5 + 6.5 signal events, corresponding to a 2.5 Οƒ significance. We determine the branching fraction B ( B 0 β†’ Ξ³ Ξ³ ) = ( 3.7 βˆ’ 1.8 + 2.2 ( stat ) Β± 0.5 ( syst ) ) Γ— 10 βˆ’ 8 and set a 90% credibility level upper limit of B ( B 0 β†’ Ξ³ Ξ³ ) < 6.4 Γ— 10 βˆ’ 8 . Published by the American Physical Society 2024

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

Measurement of the branching fractions of $$ \overline{B} $$ β†’ D(*)Kβˆ’$$ {K}_{(S)}^{\left(\ast \right)0} $$ and $$ \overline{B} $$ β†’ D(*)$$ {D}_s^{-} $$ decays at Belle II

Abstract We present measurements of the branching fractions of eight$$ {\overline{B}}^0 $$ B Β― 0 β†’D (*)+ K βˆ’ $$ {K}_{(S)}^{\left(\ast \right)0} $$ K S βˆ— 0 ,B βˆ’ β†’D (*)0 K βˆ’ $$ {K}_{(S)}^{\left(\ast \right)0} $$ K S βˆ— 0 decay channels. The results are based on data from SuperKEKB electron-positron collisions at the Ξ₯(4S) resonance collected with the Belle II detector, corresponding to an integrated luminosity of 362 fb βˆ’1 . The event yields are extracted from fits to the distributions of the difference between expected and observedBmeson energy, and are efficiency-corrected as a function ofm(K βˆ’ $$ {K}_{(S)}^{\left(\ast \right)0} $$ K S βˆ— 0 ) andm(D (*) $$ {K}_{(S)}^{\left(\ast \right)0} $$ K S βˆ— 0 ) in order to avoid dependence on the decay model. These results include the first observation of$$ {\overline{B}}^0 $$ B Β― 0 β†’D + K βˆ’ $$ {K}_S^0 $$ K S 0 ,B βˆ’ β†’D* 0 K βˆ’ $$ {K}_S^0 $$ K S 0 , and$$ {\overline{B}}^0 $$ B Β― 0 β†’D* + K βˆ’ $$ {K}_S^0 $$ K S 0 decays and a significant improvement in the precision of the other channels compared to previous measurements. The helicity-angle distributions and the invariant mass distributions of theK βˆ’ $$ {K}_{(S)}^{\left(\ast \right)0} $$ K S βˆ— 0 systems are compatible with quasi-two-body decays via a resonant transition with spin-parityJ P = 1 βˆ’ for theK βˆ’ $$ {K}_S^0 $$ K S 0 systems andJ P = 1 + for theK βˆ’ K* 0 systems. We also present measurements of the branching fractions of four$$ {\overline{B}}^0 $$ B Β― 0 β†’D (*)+ $$ {D}_s^{-} $$ D s βˆ’ ,B βˆ’ β†’D (*)0 $$ {D}_s^{-} $$ D s βˆ’ decay channels with a precision compatible to the current world averages.

Physics↗
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

Measurement of C P asymmetries in B 0 β†’ K S 0 K S 0 K S 0 decays at Belle II

We report a measurement of decay-time-dependent charge-parity ( C P ) asymmetries in B 0 β†’ K S 0 K S 0 K S 0 decays. We use 387 Γ— 10 6 B B Β― pairs collected at the Ο’ ( 4 S ) resonance with the Belle II detector at the SuperKEKB asymmetric-energy electron-positron collider. We reconstruct 220 signal events and extract the C P -violating parameters S and C from a fit to the distribution of the decay-time difference between the two B mesons. The resulting confidence region is consistent with previous measurements in B 0 β†’ K S 0 K S 0 K S 0 and B 0 β†’ ( c c Β― ) K 0 decays and with predictions based on the standard model. Published by the American Physical Society 2024

Astronomy & Astrophysics↗