RESUMEN
Using a sample of 771.6×10(6) ÏÏ(4S) decays collected by the Belle experiment at the KEKB e(+)e(-) collider, we observe, for the first time, the transition Ï(4S)âηh(b)(1P) with the branching fraction B[Ï(4S)âηh(b)(1P)]=(2.18±0.11±0.18)×10(-3) and we measure the h(b)(1P) mass M(h(b)(1P))=(9899.3±0.4±1.0) MeV/c(2), corresponding to the hyperfine (HF) splitting ΔM(HF)(1P)=(0.6±0.4±1.0) MeV/c(2). Using the transition h(b)(1P)âγη(b)(1S), we measure the η(b)(1S) mass M(η(b)(1S))=(9400.7±1.7±1.6) MeV/c(2), corresponding to ΔM(HF)(1S)=(59.6±1.7±1.6) MeV/c(2), the η(b)(1S) width Γ(η(b)(1S))=(8(-5)(+6)±5) MeV/c(2) and the branching fraction B[h(b)(1P)âγη(b)(1S)]=(56±8±4)%.
RESUMEN
The dark photon A^{'} and the dark Higgs boson h^{'} are hypothetical constituents featured in a number of recently proposed dark sector models. Assuming prompt decays of both dark particles, we search for their production in the so-called Higgstrahlung channel e^{+}e^{-}âA^{'}h^{'}, with h^{'}âA^{'}A^{'}. We investigate ten exclusive final states with A^{'}âe^{+}e^{-}, µ^{+}µ^{-}, or π^{+}π^{-} in the mass ranges 0.1 GeV/c^{2}
RESUMEN
We report the measurement of the direct CP asymmetry in the radiative B¯âX(s+dγ) decay using a data sample of (772 ± 11)×10(6) BB[over ¯] pairs collected at the Ï(4S) resonance with the Belle detector at the KEKB asymmetric-energy e(+)e(-) collider. The CP asymmetry is measured as a function of the photon energy threshold. For Eγ*≥2.1 GeV, where Eγ* is the photon energy in the center-of-mass frame, we obtain A(CP)(B¯âX(s+dγ))=(2.2±3.9±0.9)%, consistent with the standard model prediction.
