Search for lepton-flavor-violating tau-lepton decays to ℓγ at Belle

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. [Figure not available: see fulltext.]

Search for Axionlike Particles Produced in e+e- Collisions at Belle II

© 2020 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article\u27s title, journal citation, and DOI. Funded by SCOAP3. We present a search for the direct production of a light pseudoscalar a decaying into two photons with the Belle II detector at the SuperKEKB collider. We search for the process e+e-→γa, a→γγ in the mass range 0.

An inclusive measurement of the photon energy spectrum in b->s gamma decays

We report a fully inclusive measurement of the flavour changing neutral current decay b->s gamma in the energy range 1.8 GeV < E* < 2.8 GeV, covering 95% of the total spectrum. Using 140 fb^-1 we obtain BF(b->s gamma)= 3.55 +/- 0.32 +0.30-0.31 +0.11-0.07, where the errors are statistical, systematic and from theory corrections. We also measure the first and second moments of the photon energy spectrum above 1.8 GeV and obtain = 2.292 +/- 0.026 +/- 0.034 GeV and -^2 = 0.0305 +/- 0.0074 +/- 0.0063 GeV^2, where the errors are statistical and systematic.Comment: RevTex4, 6 pages, Submitted to Phys.Rev.Lett. Replaced: added table of systematic errors. New results take into account radiative J/Psi decay

Observation of Radiative Decay D0→ϕγD^0 \to \phi \gamma

We report the observation of the decay $D^{0} \to \phi \gamma$ with a statistical significance of $5.4\sigma$ in 78.1 \ifb of data collected by the Belle experiment at the KEKB $e^+ e^-$ collider. This is the first observation of a flavor-changing radiative decay of a charmed meson. The Cabibbo- and color-suppressed decays $D^0 \to \phi \pi^0$, $\phi \eta$ are also observed for the first time. We measure branching fractions \br(D^{0} \to \phi \gamma) = [ 2.60^{+0.70}_{-0.61} \stat {}^{+0.15}_{-0.17} \syst ] \times 10^{-5}, \br(D^{0} \to \phi \pi^{0}) = [ 8.01 \pm 0.26 \stat \pm 0.47 \syst ] \times 10^{-4}, and \br(D^{0} \to \phi \eta) = [ 1.48 \pm 0.47 \stat \pm 0.09 \syst ] \times 10^{-4}.Comment: 9 pages, 4 figures, Belle Preprint 2003-24, KEK Preprint 2003-75, updated version of BELLE-CONF-0346 (contributed paper to the XXI International Symposium on Lepton and Photon Interactions at High Energies,Fermilab Aug 11-16,2003). to appear in Phys. Rev. Let

Study of charmonia in four-meson final states produced in two-photon collisions

We report measurements of charmonia produced in two-photon collisions and decaying to four-meson final states, where the meson is either a charged pion or a charged kaon. The analysis is based on a 395fb^{-1} data sample accumulated with the Belle detector at the KEKB electron-positron collider. We observe signals for the three C-even charmonia eta_c(1S), chi_{c0}(1P) and chi_{c2}(1P) in the pi^+pi^-pi^+pi^-, K^+K^-pi^+pi^- and K^+K^-K^+K^- decay modes. No clear signals for eta_c(2S) production are found in these decay modes. We have also studied resonant structures in charmonium decays to two-body intermediate meson resonances. We report the products of the two-photon decay width and the branching fractions, Gamma_{gamma gamma}B, for each of the charmonium decay modes.Comment: 22 pages, 12 figure

Search for B→πℓ+ℓ−B \to \pi \ell^+\ell^- Decays at Belle

We present a search for the B-> pi e^+ e^- and B-> pi \mu^+ \mu^- decays, with a data sample of 657 million BBbar pairs collected with the Belle detector at the KEKB $e^+e^-$ collider. Signal events are reconstructed from a charged or a neutral pion candidate and a pair of oppositely charged electrons or muons. No significant signal is observed and we set the upper limit on the isospin-averaged branching fraction BF(B -> \pi \ell^+\ell^-) < 6.2x10^-8 at the 90% confidence level.Comment: 8 pages, 3 figures, accepted by PRD(RC

Study of B -> D** l nu with full reconstruction tagging

We report a study of semileptonic B decays to P-wave D** mesons. Semileptonic decay to D*_2 meson is observed for the first time and its product branching ratio is measured to be Br(B+ -> anti-D*0_2 l+nu) x Br(anti-D*0_2 -> D- pi+) = 0.22 +- 0.03(stat.) +- 0.04(syst.)%. The result is obtained using the fully reconstructed B tags from a data sample that contains 657 millions BB-bar pairs collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+ e- collider.Comment: 12 pages, 4 figures, submitted to PRD(RC

Search for new charmonium states in the processes e+ e- --> J/psi D(*) D(*) at sqrt{s} ~ 10.6 GeV

We present a study of the X(3940) state in the process e+e- -> J/psi D* Dbar. The X(3940) mass and width are measured to be (3942 +7 -6 +- 6)MeV/c^2 and Gamma=(37 + 26 - 15 +- 8 MeV. In the process e+e- -> J/psi D* D*bar we have observed another charmonium-like state, which we denote as X(4160), in the spectrum of invariant masses of D*+ D*- combinations. The X(4160) parameters are M= 4156 + 25 - 20 +- 15 MeV/c^2 and Gamma = 139 + 111 -61 +- 21 MeV. The analysis is based on a data sample with an integrated luminosity of 693 /fb recorded near the Upsilon(4S) resonance with the Belle detector at the KEKB e+ e- asymmetric-energy collider.Comment: 7 pages, 2 figures Contribution paper for conferences EPS2007 and Lepton Photon 2007, Belle-Conference-070

Measurement of the wrong-sign decays D0 -> K+ pi- pi0 and D0 -> K+ pi- pi+ pi-, and search for CP violation

Using 281 fb^-1 of data from the Belle experiment recorded at or near the Upsilon(4S) resonance, we have measured the rates of the ``wrong-sign'' decays D0 -> K+ pi- pi0 and D0 -> K+ pi- pi+ pi- relative to those of the Cabibbo-favored decays D0 -> K- pi+ pi0 and D0 -> K- pi+ pi+ pi-. These wrong-sign decays proceed via a doubly Cabibbo-suppressed amplitude or via D0-D0bar mixing; the latter has not yet been observed. We obtain R_WS(Kpipi0)=[0.229 +/-0.017(stat.) +0.013-0.009(sys.)]% and R_WS(K3pi)=[0.320 +/-0.019(stat.) +0.018-0.013(sys.)]%. The CP asymmetries are measured to be -0.006 +/- 0.053 and -0.018 +/- 0.044 for the K+ pi- pi0 and K+ pi- pi+ pi- final states, respectively.Comment: 10 pages, 3 figures, submitted to PRL, Lepton-Photon 2005 Conference in Uppsala, Sweden and HEP2005 Europhysics Conference in Lisboa, Portuga

Measurement of Branching Fractions for B→ηcK(∗)B\to \eta_c K^{(*)} Decays

We report measurements of branching fractions for charged and neutral $B\to \eta_c K$ decays where the $\eta_c$ meson is reconstructed in the $K_S^0 K^{\pm}\pi^{\mp}, K^+ K^- \pi^0, K^{*0} K^-\pi^+$ and $p \bar{p}$ decay channels. The neutral $B^0$ channel is a CP eigenstate and can be used to measure the CP violation parameter $\sin 2\phi_1$. We also report the first observation of the $B^0\to \eta_c K^{*0}$ mode. The results are based on an analysis of 29.1 fb$^{-1}$ of data collected by the Belle detector at KEKB.Comment: To appear in Physical Review Letter