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Inami, K. (ORCID:0000000327657072)

Publications and source records attributed to Inami, K. (ORCID:0000000327657072).

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

The imaging Time-of-Propagation detector at Belle II

Here, we report on the construction, operation, and performance of the Time-of-Propagation detector with imaging used for the Belle II experiment running at the Super-KEKB e + e - collider. This detector is located in the central barrel region and uses Cherenkov light to provide particle identification among hadrons. The Cherenkov light is radiated in highly polished bars of synthetic fused silica (quartz) and transported to the ends of the bars via total internal reflection. One bar end is instrumented with finely segmented micro-channel-plate photomultiplier tubes to record the light, while the other end has a mirror attached to reflect the photons back to the instrumented end. Both the propagation times and hit positions of the Cherenkov photons are measured; these depend on the Cherenkov angle and together provide good discrimination among charged pions, kaons, and protons with momenta up to around 4 GeV/ c . To date, the detector has been used to record and analyze almost 600 fb βˆ’1 of Belle II data.

43 PARTICLE ACCELERATORS↗
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

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 two-body B meson decays to Ξ› 0 and Ξ© c ( * ) 0

We report the results of the first search for Standard Model and baryon-number-violating two-body decays of the neutral B mesons to Ξ› 0 and Ξ© c ( * ) 0 using 711 fb βˆ’ 1 of data collected at the Ο’ ( 4 S ) resonance with the Belle detector at the KEKB asymmetric-energy e + e βˆ’ collider. We observe no evidence of signal from any such decays and set 95% confidence-level upper limits on the products of B 0 and B Β― 0 branching fractions for these two-body decays with B ( Ξ© c 0 β†’ Ο€ + Ξ© βˆ’ ) in the range between 9.5 Γ— 10 βˆ’ 8 and 31.2 Γ— 10 βˆ’ 8 . Published by the American Physical Society 2024

Savinov, V. (ORCID:0000000291842830)β†—
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 OSTI2024

Search for the semileptonic decays Ξ c 0 β†’ Ξ 0 β„“ + β„“ βˆ’ at Belle

Using the full data sample of 980 fb βˆ’ 1 collected with the Belle detector at the KEKB asymmetric energy electron-positron collider, we report the results of the first search for the rare semileptonic decays Ξ c 0 β†’ Ξ 0 β„“ + β„“ βˆ’ ( β„“ = e or ΞΌ ). No significant signals are observed in the Ξ 0 β„“ + β„“ βˆ’ invariant-mass distributions. Taking the decay Ξ c 0 β†’ Ξ βˆ’ Ο€ + as the normalization mode, we report 90% credibility upper limits on the branching fraction ratios B ( Ξ c 0 β†’ Ξ 0 e + e βˆ’ ) / B ( Ξ c 0 β†’ Ξ βˆ’ Ο€ + ) < 6.7 Γ— 10 βˆ’ 3 and B ( Ξ c 0 β†’ Ξ 0 ΞΌ + ΞΌ βˆ’ ) / B ( Ξ c 0 β†’ Ξ βˆ’ Ο€ + ) < 4.3 Γ— 10 βˆ’ 3 based on the phase-space assumption for signal decays. The 90% credibility upper limits on the absolute branching fractions of B ( Ξ c 0 β†’ Ξ 0 e + e βˆ’ ) and B ( Ξ c 0 β†’ Ξ 0 ΞΌ + ΞΌ βˆ’ ) are found to be 9.9 Γ— 10 βˆ’ 5 and 6.5 Γ— 10 βˆ’ 5 , respectively. Published by the American Physical Society 2024

Astronomy & Astrophysics↗
DOE OSTI2024

Search for a dark leptophilic scalar produced in association with Ο„ + Ο„ βˆ’ pair in e + e βˆ’ annihilation at center-of-mass energies near 10.58 GeV

A dark leptophilic scalar ( Ο• L ) is a hypothetical particle that couples only to leptons rather than quarks. We report on a search for Ο• L in the e + e βˆ’ β†’ Ο„ + Ο„ βˆ’ Ο• L , Ο• L β†’ β„“ + β„“ βˆ’ ( β„“ = e , ΞΌ ) process using 626 fb βˆ’ 1 of data collected by the Belle experiment near the Ο’ ( 4 S ) resonance. We validate the backgrounds with multiple control regions in data, using a novel multiclass multivariate event classifier. In absence of a signal, we quote upper limits at the 90% confidence level on the coupling between Ο• L and leptons. Our bounds, obtained in a blinded approach, are 19% more constraining than the previous limits, averaged over the mass range 0.04 ≀ m Ο• L ≀ 6.5 GeV . We exclude the parameter space below 4 GeV favored by measurement of the anomalous magnetic moment of the muon. Published by the American Physical Society 2024

Biswas, D. (ORCID:0000000275433471)β†—
DOE OSTI2024

Search for baryon and lepton number violating decays D β†’ p β„“

We search for the baryon and lepton number violating charm decays, D β†’ p β„“ , where D is either a D 0 or a D Β― 0 and β„“ is a muon or an electron, using a data sample of 921 fb βˆ’ 1 collected by the Belle detector at the KEKB asymmetric energy e + e βˆ’ collider. In the absence of significant signals, we set upper limits on the branching fractions in the range ( 5 – 8 ) Γ— 10 βˆ’ 7 at a 90% confidence level, depending on the decay mode. 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

Observation of a threshold cusp at the Ξ› Ξ· threshold in the pK - mass spectrum with Ξ›$^{+}_{c}$ β†’ pK - Ο€ + decays

We observe a narrow peaking structure in the pK - invariant-mass spectrum near the Λη threshold. The peak is clearly seen in 1.5 million events of Ξ›$^{+}_{c}$ β†’ pK - Ο€ + decay using the 980 fb -1 data sample collected by the Belle detector at the KEKB asymmetric-energy e + e - collider. We try two approaches to explain this structure: as a new resonance and as a cusp at the Λη threshold. The best fit is obtained with a coherent sum of a Flatte function and a constant background amplitude with the reduced X 2 of 257/243 (p = 0.25), while the fits to Breit-Wigner functions are unfavored by more than 7Οƒ. The best fit explains the structure as a cusp at the Λη threshold, and the obtained parameters are consistent with the known properties of Ξ›(1670). The observation gives the first identification of a threshold cusp in hadrons from the spectrum shape.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Study of the muon decay-in-flight in the Ο„ - β†’ ΞΌ - Ξ½ Β― ΞΌ Ξ½ Ο„ decay to measure the Michel parameter ΞΎ '

We present the first measurement of the Michel parameter ΞΎ' in the $\tau$ - β†’ ΞΌΒ― $\overline{v}$ ΞΌ v $\tau$ decay using the full data sample of 988 fb -1 collected by the Belle detector operating at the KEKB asymmetric energy e + ⁒e - collider. The method is based on the reconstruction of the ΞΌΒ― β†’ e⁒¯$\overline{v}$ e v ΞΌ decay-in-flight in the Belle central drift chamber and relies on the correlation between muon spin and its daughter electron momentum. We study the main sources of the background that can imitate the signal decay, such as kaon and pion decays-in-flight and charged particle scattering on the detector material. Highly efficient methods of their suppression are developed and applied to select 165 signal-candidate events. We obtain ΞΎ' = 0.22Β±0.94Β±0.42 where the first uncertainty is statistical, and the second one is systematic. The result is in agreement with the Standard Model prediction of ΞΎ' = 1.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗