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Lam, T. (ORCID:0000000191286806)

Publications and source records attributed to Lam, T. (ORCID:0000000191286806).

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

Design and commissioning of readout electronics for a $K$$^{0}_{L}$ and $ΞΌ$ detector at the Belle II experiment

The K-long and muon detector (KLM) constitutes the outer-most volume of the Belle II spectrometer at the interaction region of the SuperKEKB collider in Tsukuba, Japan. The KLM detector was partially upgraded since the Belle experiment by replacing many of its resistive-plate chambers with scintillators containing wavelength-shifting fibers and instrumenting it with silicon photomultipliers. Here, we describe the readout electronics, firmware, and software created to control and acquire data from the scintillators and resistive-plate chambers.

Belle II↗
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 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 the decay B s 0 β†’ J / ψ Ο€ 0 at Belle experiment

We have analyzed 121.4 fb βˆ’ 1 of data collected at the Ο’ ( 5 S ) resonance by the Belle experiment using the KEKB asymmetric-energy e + e βˆ’ collider to search for the decay B s 0 β†’ J / ψ Ο€ 0 . We observe no signal and report an upper limit on the branching fraction B ( B s 0 β†’ J / ψ Ο€ 0 ) of 1.21 Γ— 10 βˆ’ 5 at 90% confidence level. This result is the most stringent, improving the previous bound by 2 orders of magnitude. Published by the American Physical Society 2024

Astronomy & Astrophysics↗
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

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

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

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

First Measurement of the B + β†’ Ο€ + Ο€ 0 Ο€ 0 Branching Fraction and C P Asymmetry

We study B + β†’ Ο€ + Ο€ 0 Ο€ 0 using 711 fb -1 of data collected at the Ξ₯(4S) resonance with the Belle detector at the KEKB asymmetric-energy e + e - collider. Here we measure an inclusive branching fraction of (19.0 Β±1.5 Β±1.4)Γ—10 -6 and an inclusive CP asymmetry of (9.2 Β±6.8 Β±0.7)%, where the first uncertainties are statistical and the second are systematic, and a B + β†’ ρ(770) + Ο€ 0 branching fraction of (11.2 Β± 1.1 Β± 0.9 $^{+0.8}_{-1.6}$)Γ— 10 -6 , where the third uncertainty is due to possible interference with B + β†’ ρ(1450) + Ο€ 0 . We present the first observation of a structure around 1 GeV/c 2 in the Ο€ 0 Ο€ 0 mass spectrum, with a significance of 6.4Οƒ, and measure a branching fraction to be (6.9 Β±0.9 Β±0.6) Γ— 10 -6 . We also report a measurement of local CP asymmetry in this structure.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Study of e + e - β†’ Ξ£ 0 Ξ£ Β― 0 and Ξ£ + Ξ£ Β― - by initial state radiation method at Belle

The processes e + ⁒e - β†’Ξ£ 0 ⁒$\overline{Ξ£}$ 0 and e + ⁒e - β†’Ξ£ + ⁒$\overline{Ξ£}$ - are studied using initial-state-radiation events in a sample of 980 fb -1 collected with the Belle detector at the KEKB asymmetric-energy e + ⁒e - collider. The cross sections from the mass threshold to 3 GeV/c 2 and the effective form factors of Ξ£ 0 and Ξ£ + are measured. In the charmonium region, we observe the decays J/ψ β†’Ξ£ 0 ⁒$\overline{Ξ£}$ 0 and J/ψ β†’Ξ£ + ⁒$\overline{Ξ£}$ - and determine the respective branching fractions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗