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Hara, T. (ORCID:0000000243210417)

Publications and source records attributed to Hara, T. (ORCID:0000000243210417).

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Search for lepton-flavor-violating tau decays to β„“Ξ± at Belle

We report a search for the lepton-flavor-violating decays Ο„ Β± β†’ β„“ Β± Ξ± (β„“ = e, ΞΌ), where Ξ± is an undetected spin-0 particle, such as an axion-like particle using 736 Γ— 10 6 tau lepton pairs collected by the Belle detector at the KEKB asymmetric-energy e + e βˆ’ collider. We find no evidence of signal and obtain the most stringent upper limits on the branching fractions at 95% confidence level: $\mathcal{B}$ (Ο„ Β± β†’ e Β± Ξ±) < (0.4–6.4) Γ— 10 βˆ’4 and $\mathcal{B}$ (Ο„ Β± β†’ ΞΌ Β± Ξ±) < (0.2–3.5) Γ— 10 βˆ’4 at 95% confidence level for an Ξ± mass in the range 0.0 ≀ m Ξ± ≀ 1.6 GeV/c 2 .

tau physics↗
DOE OSTI2025

Production cross sections of light and charmed mesons in 𝑒 + ⁒𝑒 βˆ’ annihilation near 10.58 GeV

We report measurements of production cross sections for 𝜌 + , 𝜌 0 , πœ”, 𝐾* + , 𝐾* 0 , πœ™, πœ‚, 𝐾$^0_𝑆$, 𝑓 0 ⁑(980), 𝐷 + , 𝐷 0 , 𝐷$^+_𝑠$, 𝐷* + , 𝐷* 0 , and 𝐷*$^+_𝑠$ in 𝑒 + ⁒𝑒 βˆ’ collisions at a center-of-mass energy near 10.58 GeV. The data were recorded by the Belle experiment, consisting of 571 fb βˆ’1 at 10.58 GeV and 74 fb βˆ’1 at 10.52 GeV. Production cross sections are extracted as a function of the fractional hadron momentum π‘₯ 𝑝 . The measurements are compared to pythia Monte Carlo generator predictions with various fragmentation settings, including those that have increased fragmentation into vector mesons over pseudoscalar mesons. The cross sections measured for light hadrons are consistent with no additional increase of vector over pseudoscalar mesons. The charmed-meson cross sections are compared to earlier measurementsβ€”when availableβ€”including older Belle results, which they supersede. They are in agreement before application of an improved initial-state radiation correction procedure that causes slight changes in their π‘₯ 𝑝 shapes.

fragmentation functions↗
DOE OSTI2024

Evidence of h b ( 2 P ) β†’ Ο’ ( 1 S ) Ξ· Decay and Search for h b ( 1 P , 2 P ) β†’ Ο’ ( 1 S ) Ο€ 0 with the Belle Detector

We report the first evidence for the h b ( 2 P ) β†’ Ο’ ( 1 S ) Ξ· transition with a significance of 3.5 standard deviations. The decay branching fraction is measured to be B [ h b ( 2 P ) β†’ Ο’ ( 1 S ) Ξ· ] = ( 7.1 βˆ’ 3.2 + 3.7 Β± 0.8 ) Γ— 10 βˆ’ 3 , which is noticeably smaller than expected. We also set upper limits on Ο€ 0 transitions of B [ h b ( 2 P ) β†’ Ο’ ( 1 S ) Ο€ 0 ] < 1.8 Γ— 10 βˆ’ 3 , and B [ h b ( 1 P ) β†’ Ο’ ( 1 S ) Ο€ 0 ] < 1.8 Γ— 10 βˆ’ 3 , at the 90% confidence level. These results are obtained with a 131.4 fb βˆ’ 1 data sample collected near the Ο’ ( 5 S ) resonance with the Belle detector at the KEKB asymmetric-energy e + e βˆ’ collider. Published by the American Physical Society 2024

Kovalenko, E. (ORCID:0000000180841931)β†—
DOE OSTI2024

Angular analysis of B β†’ K * e + e βˆ’ in the low- q 2 region with new electron identification at Belle

We perform an angular analysis of the B β†’ K * e + e βˆ’ decay for the dielectron mass squared, q 2 , range of 0.0008 – 1.1200 GeV 2 / c 4 using the full Belle dataset in the K * 0 β†’ K + Ο€ βˆ’ and K * + β†’ K S 0 Ο€ + channels, incorporating new methods of electron identification to improve the statistical power of the dataset. This analysis is sensitive to contributions from right-handed currents from physics beyond the Standard Model by constraining the Wilson coefficients C 7 ( β€² ) . We perform a fit to the B β†’ K * e + e βˆ’ differential decay rate and measure the imaginary component of the transversality amplitude to be A T Im = βˆ’ 1.27 Β± 0.52 Β± 0.12 , and the K * transverse asymmetry to be A T ( 2 ) = 0.52 Β± 0.53 Β± 0.11 , with F L and A T Re fixed to the Standard Model values. The resulting constraints on the value of C 7 β€² are consistent with the Standard Model within a 2 Οƒ confidence interval. Published by the American Physical Society 2024

Ferlewicz, D. (ORCID:0000000243741234)β†—
DOE OSTI2024

Measurement of Angular Coefficients of B Β― β†’ D * β„“ Ξ½ Β― β„“ : Implications for | V c b | and Tests of Lepton Flavor Universality

We measure the complete set of angular coefficients J i for exclusive B Β― β†’ D * β„“ Ξ½ Β― β„“ decays ( β„“ = e , ΞΌ ). Our analysis uses the full 711 fb βˆ’ 1 Belle dataset with hadronic tag-side reconstruction. The results allow us to extract the form factors describing the B Β― β†’ D * transition and the Cabibbo-Kobayashi-Maskawa matrix element | V cb | . Using recent lattice QCD calculations for the hadronic form factors, we find | V cb | = ( 40.7 Β± 0.7 ) Γ— 10 βˆ’ 3 using the Boyd-Grinstein-Lebed parametrization, compatible with determinations from inclusive semileptonic decays. We search for lepton flavor universality violation as a function of the hadronic recoil parameter w and investigate the differences of the electron and muon angular distributions. We find no deviation from standard model expectations. Published by the American Physical Society 2024

Physics↗
DOE OSTI2024

Search for a heavy neutral lepton that mixes predominantly with the tau neutrino

We report a search for a heavy neutral lepton (HNL) that mixes predominantly with Ξ½ Ο„ . The search utilizes data collected with the Belle detector at the KEKB asymmetric energy e + e βˆ’ collider. The data sample was collected at and just below the center-of-mass energies of the Ο’ ( 4 S ) and Ο’ ( 5 S ) resonances and has an integrated luminosity of 915 fb βˆ’ 1 , corresponding to ( 836 Β± 12 ) Γ— 10 6 e + e βˆ’ β†’ Ο„ + Ο„ βˆ’ events. We search for production of the HNL (denoted N ) in the decay Ο„ βˆ’ β†’ Ο€ βˆ’ N followed by its decay via N β†’ ΞΌ + ΞΌ βˆ’ Ξ½ Ο„ . The search focuses on the parameter-space region in which the HNL is long-lived, so that the ΞΌ + ΞΌ βˆ’ originate from a common vertex that is significantly displaced from the collision point of the KEKB beams. Consistent with the expected background yield, one event is observed in the data sample after application of all the event-selection criteria. We report limits on the mixing parameter of the HNL with the Ο„ neutrino as a function of the HNL mass. 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

Evidence for B 0 β†’ p Ξ£ Β― 0 Ο€ - at Belle

We search for the B 0 β†’ p$\overline{Ξ£}$ 0 Ο€ - decay with $\overline{Ξ£}$ 0 β†’ $\overline{Ξ›}$ Ξ³, where the Ξ³ is not measured, using a data sample corresponding to an integrated luminosity of 711 fb -1 which contains 772 Γ— 10 6 B$\overline{B}$ pairs, collected around the Ξ₯(4S) resonance with the Belle detector at the KEKB asymmetric-energy e + e - collider. We measure for the first time the B 0 β†’ p$\overline{Ξ£}$ 0 Ο€ - branching fraction to be $\mathscr{B}$(B 0 β†’ p$\overline{Ξ£}$ 0 Ο€ - ) = $({1.17}_{-0.40}^{+0.43} (stat) Β± 0.07(syst))$ X 10 -6 with a significance of 3.0Οƒ. We simultaneously measure the branching fraction for the related channel B 0 β†’ p$\overline{Ξ›}$ Ο€ - with much improved precision.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Measurement of the e + e - β†’ $ {B}_s^0{\overline{B}}_s^0X $ cross section in the energy range from 10.63 to 11.02 GeV using inclusive $ {D}_s^{+} $ and D 0 production

We report the first measurement of the inclusive e + e - β†’ $b\bar{b}$ β†’ D$^Β±_s$ X and e + e - β†’ $b\bar{b}$ β†’ D 0 / $\overline{D}^0$ X cross sections in the energy range from 10.63 to 11.02 GeV. Based on these results, we determine Οƒ(e + e - β†’ ${B}_s^0{\overline{B}}_s^0$ X) and Οƒ(e + e - β†’ $B\overline{B}$ X) in the same energy range. We measure the fraction of ${B}_s^0$ events at Ξ₯(10860) to be f s = (${22.0}_{-2.1}^{+2.0}$)%. We determine also the ratio of the ${B}_s^0$ inclusive branching fractions $\mathcal{B}$(${B}_s^0$ β†’ D 0 / $\overline{D}^0$X)/$\mathcal{B}$(${B}_s^0$ β†’ ${D}_s^{\pm }$X) = 0.416 Β± 0.018 Β± 0.092. The results are obtained using the data collected with the Belle detector at the KEKB asymmetric-energy e + e - collider.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Search for the double-charmonium state with ηcJ/ψ at Belle

We measure the cross section of e + e - β†’ Ξ·cJ/ψ at the Ξ₯(nS)(n = 1–5) on-resonance and 10.52 GeV off-resonance energy points using the full data sample collected by the Belle detector with an integrated luminosity of 955 fb -1 . We also search for double charmonium production in e + e - β†’ Ξ·cJ/ψ via initial state radiation near the Ξ·cJ/ψ threshold. No evident signal of the double charmonium state is found, but evidence for the e + e - β†’ Ξ·cJ/ψ process is found with a statistical significance greater than 3.3Οƒ near the Ξ·cJ/ψ threshold. The average cross section near the threshold is measured and upper limits of cross sections are set for other regions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
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

Study of the lineshape of X ( 3872 ) using B decays to D 0 D Β― * 0 K

We present a study of the X⁑(3872) lineshape in the decay B β†’X(3872)⁒K β†’D 0 $\overline{D}$ *0 ⁒K using a data sample of 772 Γ—10 6 B$\overline{B}$ pairs collected at the Y⁑(4⁒S) resonance with the Belle detector at the KEKB asymmetric-energy e +⁒ e - collider. The peak near the threshold in the D 0 $\overline{D}$ *0 invariant mass spectrum is fitted using a relativistic Breit-Wigner lineshape. We determine the mass and width parameters to be m BW =3873.7⁒1$^{+0.56}_{-0.50⁒}$(stat) Β±0.13⁒(syst) MeV/c 2 and Ξ“ BW =5.2$^{+2.2}_{-1.5}$⁒(stat) Β±0.4⁒(syst) MeV, respectively. The branching fraction is found to be $\mathscr{B}$⁑(B + β†’ X⁑(3872)⁒K + ) Γ— $\mathscr{B}$⁑(X⁑(3872) β†’ D 0 $\overline{D}$ *0 ) = (0.9⁒7$^{+0.21}_{-0.18}$⁒(stat) Β± 0.10⁒(syst)) Γ—10 -4 . The signal from B 0 decays is observed for the first time with 5.2Οƒ significance, and the ratio of branching fractions between charged and neutral B decays is measured to be $\mathscr{B}$(B 0 β†’ X⁑(3872)⁒K 0 )/$\mathscr{B}$⁑(B + β†’X⁑(3872)⁒K + ) =1.34$^{+0.47}_{-0.40}$⁒(stat) $^{+0.10}_{-0.12}$⁒(syst). The peak is also studied using a FlattΓ© lineshape. We determine the lower limit on the D 0 $\overline{D}$ * coupling constant g to be 0.075 at 95% credibility in the parameter region where the ratio of g to the mass difference from the D 0 $\overline{D}$ *0 threshold is equal to -15.11 GeV -1 , as measured by LHCb.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Search for the Lepton Flavor Violating Decays B + β†’ K + Ο„ Β± β„“ βˆ“ ( β„“ = e , ΞΌ ) at Belle

We present a search for the lepton flavor violating decays B + β†’ K + ⁒$\tau$ ±⁒ β„“ βˆ“ , with β„“ = (e,ΞΌ), using the full data sample of 772Γ—10 6 B$\overline{B}$ pairs recorded by the Belle detector at the KEKB asymmetric-energy e + ⁒e - collider. We use events in which one B meson is fully reconstructed in a hadronic decay mode. We find no evidence for B Β± β†’ K ±⁒ $\tau$⁒ℓ decays and set upper limits on their branching fractions at the 90% confidence level in the (1 - 3) Γ— 10 -5 range. The obtained limits are the world’s best results.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

First observation of B β†’ $\bar{D}$ 1 (β†’ $\bar{D}$ Ο€ + Ο€ - ) $\ell$ + Ξ½ $\ell$ and measurement of the B β†’ $\bar{D}$ (*) Ο€$\ell$ + Ξ½ $\ell$ and B β†’ $\bar{D}$ (*) Ο€ + Ο€ - $\ell$+ Ξ½ $\ell$ branching fractions with hadronic tagging at Belle

We report measurements of the ratios of branching fractions for B β†’ $\bar{D}$(*) Ο€$\ell$+ v $\ell$ and B β†’ $\bar{D}$(*)Ο€ + Ο€ - $\ell$ + v $\ell$ relative to B β†’ $\bar{D}$*$\ell$ + v $\ell$ decays with $\ell$ = e, ΞΌ. These results are obtained from a data sample that contains 772 Γ— 10 6 $B\bar{B}$ pairs collected near the $\Upsilon$(4S) resonance with the Belle detector at the KEKB asymmetric energy e + e - collider.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Search for the decay B s 0 β†’ Ο€ 0 Ο€ 0 at Belle

We report the results of the first search for the decay B$^{0}_{s}$ β†’ Ο€ 0 ⁒π 0 using 121.4 fb -1 of data collected at the Y⁑(5⁒S) resonance with the Belle detector at the KEKB asymmetric-energy e + ⁒e - collider. We observe no signal and set a 90% confidence level upper limit of 7.7 Γ—10 -6 on the B$^{0}_{s}$ β†’ Ο€ 0 Ο€ 0 decay branching fraction.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Angular analysis of the low K + K – invariant mass enhancement in B + β†’K + K – Ο€ + decays

We study the decay B + β†’K + K – Ο€ + and investigate the angular distribution of K + K – pairs with invariant mass below 1.1 GeV / c 2 . This region exhibits both a strong enhancement in signal and very large direct CP violation. We construct a coherent sum model for the angular distribution of the S- and P-wave, and report the ratio of their amplitudes, the relative phase and the forward-backward asymmetry. We also report absolute differential branching fractions and direct CP asymmetry for the decay in bins of M K+K– and the differential branching fractions in bins of M K+π– . The results are based on a data sample that contains 772 Γ— 10 6 $B\bar{B}$ pairs collected at the $Ξ₯$(4S) resonance with the Belle detector at the KEKB asymmetric-energy e + e – collider. The result favors the presence of S- and D-waves in low M K+K– region to the detriment of a P-wave.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗