A
bstract
Charged lepton flavor violation is forbidden in the Standard Model but possible in several new physics scenarios. In many of these models, the radiative decays
τ
±
→
ℓ
±
γ
(
ℓ
=
e, μ
) are ...predicted to have a sizeable probability, making them particularly interesting channels to search at various experiments. An updated search via
τ
±
→
ℓ
±
γ
using full data of the Belle experiment, corresponding to an integrated luminosity of 988 fb
−
1
, is reported for charged lepton flavor violation. No significant excess over background predictions from the Standard Model is observed, and the upper limits on the branching fractions,
B
(
τ
±
→
μ
±
γ
) ≤ 4
.
2 × 10
−
8
and
B
(
τ
±
→
e
±
γ
) ≤ 5
.
6 × 10
−
8
, are set at 90% confidence level.
We present measurements of partial branching fractions of inclusive semileptonic B → Xuℓ+ νℓ decays using the full Belle dataset of 711 fb−1 of integrated luminosity at the Υ(4S) resonance and for ℓ ...= e, μ. Inclusive semileptonic B → Xuℓ+ νℓ decays are Cabibbo-Kobayashi-Maskawa (CKM) suppressed and measurements are complicated by the large background from CKM favored B → Xcℓ+ νℓ transitions, which have a similar signature. Using machine learning techniques, we reduce this and other backgrounds effectively, while retaining access to a large fraction of the B → Xuℓ+νℓ phase space and high signal efficiency. We measure partial branching fractions in three phase-space regions covering about 31% to 86% of the accessible B → Xuℓ+νℓ phase space. The most inclusive measurement corresponds to the phase space with lepton energies of EBℓ > 1 GeV, and we obtain ΔB ( B → Xuℓ+νℓ) = (1.59 ± 0.07 ± 0.16) × 10−3 from a two-dimensional fit of the hadronic mass spectrum and the four-momentum-transfer squared distribution, with the uncertainties denoting the statistical and systematic error. We find |Vub| = (4.10 ± 0.09 ± 0.22 ± 0.15) × 10−3 from an average of four calculations for the partial decay rate with the third uncertainty denoting the average theory error. This value is higher but compatible with the determination from exclusive semileptonic decays within 1.3 standard deviations. In addition, we report charmless inclusive partial branching fractions separately for B + and B 0 mesons as well as for electron and muon final states. No isospin breaking or lepton flavor universality violating effects are observed.
Study of γγ→γψ(2S) at Belle Wang, X. L.; Aihara, H.; Asner, D. M. ...
Physical review. D,
06/2022, Letnik:
105, Številka:
11
Journal Article
Recenzirano
Odprti dostop
Using 980 fb-1 of data at and around the Υ(nS)(n = 1, 2, 3, 4, 5) resonances collected with the Belle detector at the KEKB asymmetric-energy e+e- collider, the two-photon process γγ → γψ(2S) is ...studied from the threshold to 4.2 GeV for the first time. Two structures are seen in the invariant mass distribution of γψ(2S): one at MR1 = 3922.4 ± 6.5 ± 2.0 MeV/c2 with a width of ΓR1 = 22 ± 17 ± 4 MeV, and another at MR2 = 4014.3 ± 4.0 ± 1.5 MeV/c2 with a width of ΓR2 = 4 ± 11 ± 6 MeV; the signals are parametrized with the incoherent sum of two Breit- Wigner functions. The first structure is consistent with the X(3915) or the χc2(3930), and the local statistical significance is determined to be 3.1σ with the systematic uncertainties included. The second matches none of the known charmonium or charmonium like states, and its global significance is determined to be 2.8σ including the look-elsewhere effect. The production rates are Γγγ B(R1 → γψ(2S)) = 9.8 ± 3.6 ± 1.2 eV assuming (JPC, |λ|) = (0++, 0) or 2.0 ± 0.7 ± 0.2 eV with (2++, 2) for the first structure and Γγγ B(R2 → γψ(2S)) = 6.2 ± 2.2 ± 0.8 eV with (0++, 0) or 1.2 ± 0.4 ± 0.2 eV with (2++, 2) for the second one. Furthermore, the first errors are statistical and the second systematic, and λ is the helicity.
We report results from a study of the spin and parity of Ξ c ( 2970 ) + using a 980 fb −1 data sample collected by the Belle detector at the KEKB asymmetric-energy e+e− collider. The decay angle ...distributions in the chain Ξc (2970)+→ Ξc (2645) 0π+ → Ξ+c π− π+ are analyzed to determine the spin of this charmed-strange baryon. The angular distributions strongly favor the Ξc (2970)+ spin J = 1/2 over 3/2 or 5/2, under an assumption that the lowest partial wave dominates in the decay. We also measure the ratio of Ξc (2970)+ decay branching fractions R = B Ξc (2970)+ → Ξc (2645)0π+/B Ξc (2970)+ → Ξ0c π+ = 1.67 ± 0.29 (stat)+0.15 −0.09 (syst) ± 0.25 (IS), where the last uncertainty is due to possible isospin-symmetry-breaking effects. This R value favors the spin-parity J P = 1/2+ with the spin of the light-quark degrees of freedom sl = 0. This is the first determination of the spin and parity of a charmed-strange baryon.
We report measurements of the branching fractions of singly Cabibbo-suppressed decays Λc+ → pη and Λc+ → pπ0 using the full Belle data sample corresponding to an integrated luminosity of 980.6 ...fb−1. The data were collected by the Belle detector at the KEKB e+ e− asymmetric energy collider. A clear Λ + c signal is seen in the invariant mass distribution of p η . The fitted number of signal events of the Λc+ → pη process is 7734 ± 263 ; from this, we measure the ratio of branching fractions B ( Λc+→ pη ) / B ( Λc+ → pK− π+ ) = 2.258 ± 0. 077 ( stat ) ± 0.122 ( syst ) × 10 − 2 , from which we infer the branching fraction B ( Λc+ → pη ) = 1.42 ± 0.05 ( stat ) ± 0.11 ( syst ) × 10−3. In addition, no significant signal for Λc+ → pπ0 is found, so an upper limit on the branching fraction of B ( Λc+ → pπ0) < 8.0 × 10−5 at a 90% credibility level is set, more than 3 times better than the best current upper limit.
We present a search for the lepton flavor violating decays B^{+}→K^{+}τ^{±}ℓ^{∓}, with ℓ=(e,μ), using the full data sample of 772×10^{6} BBover ¯ 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^{±}→K^{±}τℓ decays and set upper limits on their branching fractions at the 90% confidence level in the (1-3)×10^{-5} range. The obtained limits are the world's best results.
The measurement of two-particle angular correlation functions in high-multiplicity e^{+}e^{-} collisions at sqrts=10.52 GeV is reported. In this study, the 89.5 fb^{-1} of hadronic e^{+}e^{-} ...annihilation data collected by the Belle detector at KEKB are used. Two-particle angular correlation functions are measured in the full relative azimuthal angle (Δϕ) and three units of pseudorapidity (Δη), defined by either the electron beam axis or the event-shape thrust axis, and are studied as a function of charged-particle multiplicity. The measurement in the thrust axis analysis, with mostly outgoing quark pairs determining the reference axis, is sensitive to the region of additional soft gluon emissions. No significant anisotropic collective behavior is observed with either coordinate analyses. Near-side jet correlations appear to be absent in the thrust axis analysis. The measurements are compared to predictions from various event generators and are expected to provide new constraints to the phenomenological models in the low-energy regime.
PDF
