Recent results from CLEOII: charm physics

Abstract

In the last decade the CLEO II collaboration, using the CESR e + e − storage ring, has accumulated nearly 15 fb −1 of luminosity. in the energy region around 10.5 GeV, corresponding to the production of more than 3·10 7 charmed particles (apart from daughters of B meson decay). This has produced new results in the spectroscopy of charmed baryons and mesons and a much improved limit on D 0 - D 0 mixing. We present evidence for an excitation of the Ξ c , seen in both charge states; namely, the Ξ′ c , the J p = 1 2 + c{sq} state, which is symmetric under exchange of light quark quantum numbers. Another state is seen in the decays to Ξ c + π + π − and Ξ c 0 π + π − via an intermediate Ξ c ∗ , and is consistent with the Ξ c1 , the J p = 3 2 − p-wave state analogous to the Λ c1 +(2625). The mass differences relative to the ground state are: M( Ξ c +′) − M( Ξ c ) = (107.8 ± 1.7 ± 2.5) MeV/ c 2, M( Ξ c 0′) − M( Ξ c ) = (107.0 ± 1.5 ± 2.5) MeV/ c 2, M( Ξ c1 +) − M( Ξ c +) = (348.6 ± 0.6 ± 1.0) MeV/ c 2, and M( Ξ c1 0) − M( Ξ c 0) = (347.2 ± 0.7 ± 2.0) MeV/ c 2. We have made the first (preliminary) measurements of the natural widths of the Σ c ++ and Σ c 0 baryons: Γ ++ = (2.98 −.35 +.38 ± 0.5) MeV, and Γ 0 = (2.63 −.33 +.36 ± 0.5) MeV. In the charmed meson sector we find evidence for a wide 1 + state, the D 1 0(2460). Its mass is (2.461 −.034 +.041 ± .010 ± .032) GeV; its width is (290 −74 +101 ± 26 ± 36) MeV. We find no supporting evidence for the D ∗′+ , a purported radial excitation claimed by the Delphi group at a mass of (2637 ± 2 ± 6) MeV. Finally we are able, using “wrong-sign” (DCSD) Kπ decays to make the following measurements: 1) the observed ratio of DCSD decays relative to the Cabibbo-allowed rate is R ws = (0.34 ± 0.7 ± .06)%, 2) the mixing parameters are bounded, at 95% confidence, by x ′2 < .001 and −.059 < y′ < .003. x′ and y′ are, in the absence of final state phase differences, the real and imaginary parts of | frsol| δM/ Γ.