Photometric Compliance of Tablet Screens and Retro-Illuminated Acuity Charts As Visual Acuity Measurement Devices.

Mobile technology is increasingly used to measure visual acuity. Standards for chart-based acuity tests specify photometric requirements for luminance, optotype contrast and luminance uniformity. Manufacturers provide some photometric data but little is known about tablet performance for visual acuity testing. This study photometrically characterised seven tablet computers (iPad, Apple inc.) and three ETDRS (Early Treatment Diabetic Retinopathy Study) visual acuity charts with room lights on and off, and compared findings with visual acuity measurement standards. Tablet screen luminance and contrast were measured using nine points across a black and white checkerboard test screen at five arbitrary brightness levels. ETDRS optotypes and adjacent white background luminance and contrast were measured. All seven tablets (room lights off) exceeded the most stringent requirement for mean luminance (≥ 120 cd/m2) providing the nominal brightness setting was above 50%. All exceeded contrast requirement (Weber ≥ 90%) regardless of brightness setting, and five were marginally below the required luminance uniformity threshold (Lmin/Lmax ≥ 80%). Re-assessing three tablets with room lights on made little difference to mean luminance or contrast, and improved luminance uniformity to exceed the threshold. The three EDTRS charts (room lights off) had adequate mean luminance (≥ 120 cd/m2) and Weber contrast (≥ 90%), but all three charts failed to meet the luminance uniformity standard (Lmin/Lmax ≥ 80%). Two charts were operating beyond manufacturer's recommended lamp replacement schedule. With room lights on, chart mean luminance and Weber contrast increased, but two charts still had inadequate luminance uniformity. Tablet computers showed less inter-device variability, higher contrast, and better luminance uniformity than charts in both lights-on and lights-off environments, providing brightness setting was >50%. Overall, iPad tablets matched or marginally out-performed ETDRS charts in terms of photometric compliance with high contrast acuity standards

Higher-order multipole amplitudes in charmonium radiative transitions

Using 24 million $\psi' \equiv \psi(2S)$ decays in CLEO-c, we have searched for higher multipole admixtures in electric-dipole-dominated radiative transitions in charmonia. We find good agreement between our data and theoretical predictions for magnetic quadrupole (M2) amplitudes in the transitions $\psi' \to \gamma \chi_{c1,2}$ and $\chi_{c1,2} \to \gamma J/\psi$, in striking contrast to some previous measurements. Let $b_2^J$ and $a_2^J$ denote the normalized M2 amplitudes in the respective aforementioned decays, where the superscript $J$ refers to the angular momentum of the $\chi_{cJ}$. By performing unbinned maximum likelihood fits to full five-parameter angular distributions, we determine the ratios $a_2^{J=1}/a_2^{J=2} = 0.67^{+0.19}_{-0.13}$ and $a_2^{J=1}/b_2^{J=1} = -2.27^{+0.57}_{-0.99}$, where the theoretical predictions are independent of the charmed quark magnetic moment and are $a_2^{J=1}/a_2^{J=2} = 0.676 \pm 0.071$ and $a_2^{J=1}/b_2^{J=1} = -2.27 \pm 0.16$.Comment: 32 pages, 7 figures, acceptance updat

Measurements of D Meson Decays to Two Pseudoscalar Mesons

Using data collected on the psi(3770) resonance and near the Ds*+ Ds- peak production energy by the CLEO-c detector, we study the decays of the possible D->PP modes and report measurements of or upper limits on all branching fractions for Cabibbo-favored, singly-Cabibbo-suppressed, and doubly-Cabibbo-suppressed D->PP decays except modes involving K0L (and except D0->K+ pi-). We normalize with respect to the Cabibbo-favored D modes, D0->K- pi+, D+->K- pi+ pi+, and Ds+->K+ K0S.Comment: 11 pages, 2 figures, available through http://www.lns.cornell.edu/public/CLNS/, submitted to PR

Evidence for Decays of h_c to Multi-Pion Final States

Using a sample of 2.59 x 10^7 psi(2S) decays collected by the CLEO--c detector, we present results of a search for the decay chain psi(2S) -> pi^0 h_c, h_c -> n(pi^+ pi^-) pi^0, n=1,2,3. We observe no significant signals for n=1 and n=3 and set upper limits for the corresponding decay rates. First evidence for the decay h_c {\o}pi^+ pi^- pi^+ pi^- pi^0 is presented, and a product branching fraction of B(psi(2S) -> h_c) x B(h_c -> 2(pi^+ pi^-) pi^0)=1.88^{+0.48+0.47}_{-0.45-0.30} x 10^{-5} is measured. This result implies that h_c -> hadrons and h_c -> gamma eta_c have comparable rates, in agreement with expectations.Comment: Available through http://www.lns.cornell.edu/public/CLNS/, submitted to Phys. Rev. D. (Rapid Communications

Study of the semileptonic decay Ds+ -> f0(980) e+ nu and implications for Bs -> J/psi f0

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)%.Comment: 19 pages, 9 figures, to be published in Physical Review

Ds+ Exclusive Hadronic Decays Involving omega

Using data collected near the Ds*+ Ds- peak production energy Ecm=4170 MeV by the CLEO-c detector, we search for Ds+ exclusive hadronic decays involving omega. We find B(Ds+ -> pi+ omega) = (0.21 +- 0.09 +- 0.01)%, B(Ds+ -> pi+ pi0 omega) = (2.78 +- 0.65 +- 0.25)%, B(Ds+ -> pi+ pi+ pi- omega) = (1.58 +- 0.45 +- 0.09)%, B(Ds+ -> pi+ eta omega) = (0.85 +- 0.54 +- 0.06)%, B(Ds+ -> K+ omega) K+ pi0 omega) K+ pi+ pi- omega) K+ eta omega) <0.79%. The upper limits are at 90% confidence level.Comment: 8 pages, 3 figures, available through http://www.lns.cornell.edu/public/CLNS/, submitted to PR