K. Y. Gao

Improved measurements of D meson semileptonic decays to π and K mesons

Using the entire CLEO-c {psi}(3770){yields}DD event sample, corresponding to an integrated luminosity of 818 pb{sup -1} and approximately 5.4x10{sup 6} DD events, we present a study of the decays D{sup 0}{yields}{pi}{sup -}e{sup +}{nu}{sub e}, D{sup 0}{yields}K{sup -}e{sup +}{nu}{sub e}, D{sup +}{yields}{pi}{sup 0}e{sup +}{nu}{sub e}, and D{sup +}{yields}K{sup 0}e{sup +}{nu}{sub e}. Via a tagged analysis technique, in which one D is fully reconstructed in a hadronic mode, partial rates for semileptonic decays by the other D are measured in several q{sup 2} bins. We fit these rates using several form factor parametrizations and report the results, including form factor shape parameters and the branching fractions B(D{sup 0}{yields}{pi}{sup -}e{sup +}{nu}{sub e})=(0.288{+-}0.008{+-}0.003)%, B(D{sup 0}{yields}K{sup -}e{sup +}{nu}{sub e})=(3.50{+-}0.03{+-}0.04)%, B(D{sup +}{yields}{pi}{sup 0}e{sup +}{nu}{sub e})=(0.405{+-}0.016{+-}0.009)%, and B(D{sup +}{yields}K{sup 0}e{sup +}{nu}{sub e})=(8.83{+-}0.10{+-}0.20)%, where the first uncertainties are statistical and the second are systematic. Taking input from lattice quantum chromodynamics, we also find |V{sub cd}|=0.234{+-}0.007{+-}0.002{+-}0.025 and |V{sub cs}|=0.985{+-}0.009{+-}0.006{+-}0.103, where the third uncertainties are from lattice quantum chromodynamics.

Measurements of D meson decays to two pseudoscalar mesons

Using data collected on the {psi}(3770) resonance and near the D{sub s}*{sup {+-}D}{sub s}{sup {+-}}peak production energy by the CLEO-c detector, we study the decays of the possible D{yields}PP modes and report measurements of or upper limits on all branching fractions for Cabibbo-favored, singly Cabibbo-suppressed, and doubly Cabibbo-suppressed D{yields}PP decays except modes involving K{sub L}{sup 0} (and except D{sup 0{yields}}K{sup +{pi}-}). We normalize with respect to the Cabibbo-favored D modes, D{sup 0{yields}}K{sup -{pi}+}, D{sup +{yields}}K{sup -{pi}+{pi}+}, and D{sub s}{sup +{yields}}K{sup +}K{sub S}{sup 0}.

Measurement of the ηb(1S) mass and the branching fraction for Υ(3S)→γηb(1S)

We report evidence for the ground state of bottomonium, eta_b(1S), in the radiative decay Upsilon(3S) --> gamma eta_b in e^+e^- annihilation data taken with the CLEO III detector. Using 6 million Upsilon(3S) decays, and assuming Gamma(eta_b) = 10 MeV/c^2, we obtain B(Upsilon(3S) --> gamma eta_b) = (7.1 +- 1.8 +- 1.1) X 10^{-4}, where the first error is statistical and the second is systematic. The statistical significance is about 4 sigma. The mass is determined to be M(eta_b) = 9391.8 +- 6.6 +- 2.0 MeV/c^2, which corresponds to the hyperfine splitting Delta M_{hf}(1S)_b = 68.5 +- 6.6 +- 2.0 MeV/c^2. Using 9 million Upsilon(2S) decays, we place an upper limit on the corresponding Y(2S) decay, B(Y(2S) --> gamma eta_b) < 8.4 X 10^{-4} at 90 % confidence level.

Dalitz plot analysis of Ds+→K+K-π+

We perform a Dalitz plot analysis of about 100,000 Ds+ decays to K+ K- pi+ and measure the complex amplitudes of the intermediate resonances which contribute to this decay mode. We also measure the relative branching fractions of Ds+ -->K+ K+ pi- and Ds+ -->K+ K+ K-. For this analysis we use a 384 fb-1 data sample, recorded by the BABAR detector at the PEP-II asymmetric-energy e+e- collider running at center-of-mass energies near 10.58 GeV.We perform a Dalitz plot analysis of about 100 000 Ds+ decays to K+K-π+ and measure the complex amplitudes of the intermediate resonances which contribute to this decay mode. We also measure the relative branching fractions of Ds+→K+K+π- and Ds+→K+K+K-. For this analysis we use a 384 fb-1 data sample, recorded by the BABAR detector at the PEP-II asymmetric-energy e+e- collider running at center-of-mass energies near 10.58 GeV.

Study of the semileptonic decay Ds+→f0(980)e+ν and implications for Bs0→J/ψf0

Using e+e- -> Ds^-Ds^{*+} and Ds^{*-}Ds^+ interactions at 4170 MeV collected with the CLEO-c detector, we investigate the semileptonic decays Ds+ -> f0(980) e+ nu, and Ds+ -> phi e+ nu. By examining the decay rates as functions of the four-momentum transfer squared, q^2, we measure the ratio [dB/dq^2(Ds+ -> f0(980) e+ nu) B(f0 -> pi+pi-)]/[dB/dq^2(Ds+ -> phi e+ nu)B(phi -> K+K-)] at q^2 of zero to be (42 +/- 11)%. This ratio has been predicted to equal the rate ratio [B(Bs -> J/psi f_0)B(f0 -> pi+pi-)]/[B(Bs -> J/psi phi)B(phi -> K+K-)], thus indicating that the CP eigenstate J/psi f0 could be useful for measuring CP violation via Bs mixing. Assuming a simple pole model for the form factor |f+(q^2)| in the f0 e+ nu decay, we find a pole mass of (1.7 {+4.5} {-0.7} +/- 0.2) GeV. We also determine the f0 mass and width as (977 {+11}{-9} +/- 1) MeV, and (91{+30}{-22}+/- 3) MeV, respectively. In addition, we present updated results for B(Ds+ -> f0(980) e+ nu) B(f0 -> pi+pi-)=(0.20 +/- 0.03 +/- 0.01)%, and B}(Ds+ -> phi e+ nu)=(2.36 +/- 0.23 +/- 0.13)%.

Measurement of the pseudoscalar decay constant fDs using Ds+→τ+ν, τ+→ρ+ν̄ decays

Analyzing 600 pb of ee collisions at 4170 MeV center-of-mass energy with the CLEOc detector, we measure the branching fraction B(D s → τ ν) = (5.52 ± 0.57 ± 0.21)% using the τ → ρν decay mode. Combining with other CLEO measurements of B(D s → τ ν) we determine the pseudoscalar decay constant fDs = (259.7 ± 7.8± 3.4) MeV consistent with the value obtained from our D s → μ ν measurement of (257.6± 10.3± 4.3) MeV. Combining these measurements we find a value of fDs = (259.0± 6.2± 3.0) MeV, that differs from the most accurate prediction based on unquenched lattice gauge theory of (241 ± 3) MeV by 2.4 standard deviations. We also present the first measurements of B(D s → K ππ) = (1.00 ± 0.18 ± 0.04)%, and B(D s → π ππ) = (0.65 ± 0.13 ± 0.03)%, and measure a new value for B(D s → ηρ ) = (8.9 ± 0.6 ± 0.5)%. PACS numbers: 13.20.Fc, 12.38.Gc, 14.40.LbAnalyzing 600 pb ―1 of e + e ― collisions at 4170 MeV center-of-mass energy with the CLEO-c detector, we measure the branching fraction B(D + s → τ + ν) = (5.52 ± 0.57 ± 0.21)% using the τ + → ρ + ν decay mode. Combining with other CLEO measurements of B(D + s → τ + ν) we determine the pseudoscalar decay constant f Ds = (259.7 ± 7.8 ± 3.4) MeV consistent with the value obtained from our D + s → μ + ν measurement of (257.6 ± 10.3 ± 4.3) MeV. Combining these measurements we find a value of f Ds = (259.0 ± 6.2 ± 3.0) MeV, that differs from the most accurate prediction based on unquenched lattice gauge theory of (241 ± 3) MeV by 2.4 standard deviations. We also present the first measurements of B(D + s → K 0 π + π 0 ) = (1.00 ± 0.18 ± 0.04)%, and B(D + s → π + π 0 π 0 ) (0.65 ± 0.13 ± 0.03)%, and measure a new value for B(D + s → ηρ + ) = (8.9 ± 0.6 ± 0.5)%.

Study of the semileptonic decay D(s)+ ---> f0(980) e+ nu and implications for B(s) ---> J/psi f(0)

Using e+e- -> Ds^-Ds^{*+} and Ds^{*-}Ds^+ interactions at 4170 MeV collected with the CLEO-c detector, we investigate the semileptonic decays Ds+ -> f0(980) e+ nu, and Ds+ -> phi e+ nu. By examining the decay rates as functions of the four-momentum transfer squared, q^2, we measure the ratio [dB/dq^2(Ds+ -> f0(980) e+ nu) B(f0 -> pi+pi-)]/[dB/dq^2(Ds+ -> phi e+ nu)B(phi -> K+K-)] at q^2 of zero to be (42 +/- 11)%. This ratio has been predicted to equal the rate ratio [B(Bs -> J/psi f_0)B(f0 -> pi+pi-)]/[B(Bs -> J/psi phi)B(phi -> K+K-)], thus indicating that the CP eigenstate J/psi f0 could be useful for measuring CP violation via Bs mixing. Assuming a simple pole model for the form factor |f+(q^2)| in the f0 e+ nu decay, we find a pole mass of (1.7 {+4.5} {-0.7} +/- 0.2) GeV. We also determine the f0 mass and width as (977 {+11}{-9} +/- 1) MeV, and (91{+30}{-22}+/- 3) MeV, respectively. In addition, we present updated results for B(Ds+ -> f0(980) e+ nu) B(f0 -> pi+pi-)=(0.20 +/- 0.03 +/- 0.01)%, and B}(Ds+ -> phi e+ nu)=(2.36 +/- 0.23 +/- 0.13)%.

Charmonium decays to γπ0, γη, and γη′

Using data acquired with the CLEO-c detector at the CESR e + e - collider, we measure branching fractions for J/ψ, ψ(2S), and ψ(3770) decays to γπ 0 γη, and γηʹ. Defining R n ≡ B[ψ(nS)→ γη]/B[ψ(nS) → γηʹ], we obtain R 1 = (21.1 ± 0.9)% and, unexpectedly, an order of magnitude smaller limit, R 2 < 1.8% at 90% C.L. We also use J/ψ→ γηʹ events to determine branching fractions of improved precision for the five most copious ηʹ decay modes.

Charmonium decays to gamma pi(0), gamma eta, and gamma eta '

Using data acquired with the CLEO-c detector at the CESR e + e - collider, we measure branching fractions for J/ψ, ψ(2S), and ψ(3770) decays to γπ 0 γη, and γηʹ. Defining R n ≡ B[ψ(nS)→ γη]/B[ψ(nS) → γηʹ], we obtain R 1 = (21.1 ± 0.9)% and, unexpectedly, an order of magnitude smaller limit, R 2 < 1.8% at 90% C.L. We also use J/ψ→ γηʹ events to determine branching fractions of improved precision for the five most copious ηʹ decay modes.

Search for the decay J/ψ → γ + invisible

A search for J/ψ radiative decay to weakly interacting neutral final states was performed using the CLEO-c detector at the Cornell Electron Storage Ring. J/ψ events were selected by observing the hadronic decay ψ (2S) → π + π - J/ψ. A total of 3.7 X 10 6 J/ψ events were used to study the decay J/ψ → y + X, where X is a narrow state that is invisible to the detector. No significant signal was observed, and upper limits on the branching fraction were set for masses m X up to 960 MeV/c 2 . The upper limit corresponding to m X = 0 is 4.3 × 10- 6 at the 90% confidence level.