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Kumara, K. (ORCID:0000000315725365)

Publications and source records attributed to Kumara, K. (ORCID:0000000315725365).

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

Search for charmed baryons in the Ξ› c + Ξ· system and measurement of the branching fractions of Ξ› c ( 2880 ) + and Ξ› c ( 2940 ) + decaying to Ξ› c + Ξ· and p D 0 relative to Ξ£ c ( 2455 ) Ο€

We search for excited charmed baryons in the Ξ› c + Ξ· system using a data sample corresponding to an integrated luminosity of 980 fb βˆ’ 1 . The data were collected by the Belle detector at the KEKB e + e βˆ’ asymmetric-energy collider. No significant signals are found in the Ξ› c + Ξ· mass spectrum, including the known Ξ› c ( 2880 ) + and Ξ› c ( 2940 ) + . Clear Ξ› c ( 2880 ) + and Ξ› c ( 2940 ) + signals are observed in the p D 0 mass spectrum. We set upper limits at 90% credibility level on ratios of branching fractions of Ξ› c ( 2880 ) + and Ξ› c ( 2940 ) + decaying to Ξ› c + Ξ· relative to Ξ£ c ( 2455 ) Ο€ of < 0.13 for the Ξ› c ( 2880 ) + and < 1.11 for the Ξ› c ( 2940 ) + . We measure ratios of branching fractions of Ξ› c ( 2880 ) + and Ξ› c ( 2940 ) + decaying to p D 0 relative to Ξ£ c ( 2455 ) Ο€ of 0.75 Β± 0.03 ( stat ) Β± 0.07 ( syst ) for the Ξ› c ( 2880 ) + and 3.59 Β± 0.21 ( stat ) Β± 0.56 ( syst ) for the Ξ› c ( 2940 ) + . Published by the American Physical Society 2024

Astronomy & Astrophysics↗
DOE OSTI2024

Measurements of the Branching Fraction, Polarization, and C P Asymmetry for the Decay B 0 β†’ Ο‰ Ο‰

We present a comprehensive study of B 0 β†’ Ο‰ Ο‰ decays using 772 Γ— 10 6 B B Β― pairs collected with the Belle detector at the KEKB e + e βˆ’ collider. This process is a suppressed charmless decay into two vector mesons and can exhibit interesting polarization and C P violation. The decay is observed for the first time with a significance of 7.9 standard deviations. We measure a branching fraction B = ( 1.53 Β± 0.29 Β± 0.17 ) Γ— 10 βˆ’ 6 , a fraction of longitudinal polarization f L = 0.87 Β± 0.13 Β± 0.13 , and a time-integrated C P asymmetry A C P = βˆ’ 0.44 Β± 0.43 Β± 0.11 , where the first uncertainties listed are statistical and the second are systematic. This is the first observation of B 0 β†’ Ο‰ Ο‰ and the first measurements of f L and A C P for this decay. Published by the American Physical Society 2024

Physics↗
DOE OSTI2024

Search for Baryon-Number-Violating Processes in B βˆ’ Decays to the Ξ Β― c 0 Ξ› Β― c βˆ’ Final State

We report the results of the first search for B βˆ’ decays to the Ξ Β― c 0 Ξ› Β― c βˆ’ final state 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. The results are interpreted in terms of both direct baryon-number-violating B βˆ’ decay and Ξ c 0 βˆ’ Ξ Β― c 0 oscillations which follow the standard model decay B βˆ’ β†’ Ξ c 0 Ξ› Β― c βˆ’ . We observe no evidence for baryon number violation and set the 95% confidence-level upper limits on the ratio of baryon-number-violating and standard model branching fractions B ( B βˆ’ β†’ Ξ Β― c 0 Ξ› Β― c βˆ’ ) / B ( B βˆ’ β†’ Ξ c 0 Ξ› Β― c βˆ’ ) to be < 2.7 % and on the effective angular frequency of mixing Ο‰ in Ξ c 0 βˆ’ Ξ Β― c 0 oscillations to be < 0.76 ps βˆ’ 1 (equivalent to Ο„ mix > 1.3 ps ). Published by the American Physical Society 2024

Physics↗
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 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

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

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

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↗
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↗