Search for: All records

A bstract We present the first measurement of the branching fraction of the singly Cabibbo-suppressed (SCS) decay $$ {\Lambda}_c^{+} $$ Λ c + → pη ′ with η ′ → ηπ + π − , using a data sample corresponding to an integrated luminosity of 981 fb − 1 , collected by the Belle detector at the KEKB e + e − asymmetric-energy collider. A significant $$ {\Lambda}_c^{+} $$ Λ c + → pη ′ signal is observed for the first time with a signal significance of 5.4 σ . The relative branching fraction with respect to the normalization mode $$ {\Lambda}_c^{+} $$ Λ c + → pK − π + is measured to be $$ \frac{\mathcal{B}\left({\Lambda}_c^{+}\to p\eta^{\prime}\right)}{\mathcal{B}\left({\Lambda}_c^{+}\to {pK}^{-}{\pi}^{+}\right)}=\left(7.54\pm 1.32\pm 0.73\right)\times {10}^{-3}, $$ B Λ c + → pη ′ B Λ c + → pK − π + = 7.54 ± 1.32 ± 0.73 × 10 − 3 , where the uncertainties are statistical and systematic, respectively. Using the world-average value of $$ \mathcal{B}\left({\Lambda}_c^{+}\to {pK}^{-}{\pi}^{+}\right) $$ B Λ c + → pK − π + = (6 . 28 ± 0 . 32) × 10 − 2 , we obtain $$ \mathcal{B}\left({\Lambda}_c^{+}\to p\eta^{\prime}\right)=\left(4.73\pm 0.82\pm 0.46\pm 0.24\right)\times {10}^{-4}, $$ B Λ c + → pη ′ = 4.73 ± 0.82 ± 0.46 ± 0.24 × 10 − 4 , where the uncertainties are statistical, systematic, and from $$ \mathcal{B}\left({\Lambda}_c^{+}\to {pK}^{-}{\pi}^{+}\right) $$ B Λ c + → pK − π + , respectively. 

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, $$ \mathcal{B} $$ B ( τ ± → μ ± γ ) ≤ 4 . 2 × 10 − 8 and $$ \mathcal{B} $$ B ( τ ± → e ± γ ) ≤ 5 . 6 × 10 − 8 , are set at 90% confidence level.