English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

We use a simple perturbation theory argument and measurements of charmoniumleptonic widths $\Gamma (\psi_{NS} \rightarrow e^+e^-)$ to estimate the ratio\mbox{$R_\circ \equiv {\vert \Psi _{\eta_{c1S}}(0) \vert}^2/{\vert\Psi_{\psi_{1 S}}(0)\vert}^2$} in the general context of non-relativistic potential models. We obtain $R_\circ = 1.4 \pm 0.1$. We then applywell known potential model formulas, which include lowest order QCDcorrections, to find $\Gamma (\eta_c \rightarrow \gamma \gamma )/\Gamma(\psi_{1S} \rightarrow e^+e^-) \approx 2.2\pm 0.2$. The central value for$\Gamma (\psi_{1S} \rightarrow e^+ e^-)$in the 1992 Particle Data Tables thenleads to a (non relativistic) prediction $\Gamma (\eta_c \rightarrow \gamma\gamma )\approx 11.8\pm 0.8 $ keV. This prediction is in good agreement with arecent measurement by the ARGUS collaboration, is consistent with a recentmeasurement by the L3 collaboration but is significantly higher than severalearlier measurements and than previous theoretical estimates, which usuallyassume $R_\circ =1$. The correction to $R_\circ =1$ is estimated to be smallerbut nonnegligible for the $b\bar b$ system. Using the current centralmeasurement for $\Gamma (\Upsilon_{1S}\rightarrow e^+e^-)$ we find $\Gamma(\eta_b\rightarrow \gamma \gamma )\approx 0.58\pm 0.03$ keV. A rough estimateof relativistic corrections reduces the expected two photon rates to about 8.8keV and 0.52 keV for the $\eta_c$ and $\eta_b$ mesons respectively. SuchcorrectionsComment: Estimates of likely relativistic corrections to the results have been  adde

physical review. d. particles, fields, gravitation, and cosmology/physical review. d. particles and fields

Decays<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">η</mml:mi></mml:mrow><mml:mrow><mml:mi mathvariant="italic">c</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math>→γγ and<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">η</mml:mi></mml:mrow><mml:mrow><mml:mi mathvariant="italic">b</mml:mi></mml:mrow></mml:msub></mml:mrow></…

Decaysηc→γγ andηb