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 Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

Based on a data sample of 10 billion $J/\psi$ events collected with theBESIII detector, improved measurements of the Dalitz decays$\eta/\eta'\rightarrow\gamma e^+e^-$ are performed, where the $\eta$ and$\eta'$ are produced through the radiative decays $J/\psi\rightarrow\gamma\eta/\eta'$. The branching fractions of $\eta\rightarrow\gamma e^+e^-$ and$\eta'\rightarrow\gamma e^+e^-$ are measured to be $(7.07 \pm 0.05 \pm0.23)\times10^{-3}$ and $(4.83\pm0.07\pm0.14)\times10^{-4}$, respectively.Within the single pole model, the parameter of electromagnetic transition formfactor for $\eta\rightarrow\gamma e^+e^-$ is determined to be$\Lambda_{\eta}=(0.749 \pm 0.027 \pm 0.007)~ {\rm GeV}/c^{2}$. Within themulti-pole model, we extract the electromagnetic transition form factors for$\eta'\rightarrow\gamma e^+e^-$ to be $\Lambda_{\eta'} = (0.802 \pm 0.007\pm0.008)~ {\rm GeV}/c^{2}$ and $\gamma_{\eta'} = (0.113\pm0.010\pm0.002)~ {\rmGeV}/c^{2}$. The results are consistent with both theoretical predictions andprevious measurements. The characteristic sizes of the interaction regions forthe $\eta$ and $\eta'$ are calculated to be $(0.645 \pm 0.023 \pm 0.007 )~ {\rmfm}$ and $(0.596 \pm 0.005 \pm 0.006)~ {\rm fm}$, respectively. In addition, wesearch for the dark photon in $\eta/\eta^\prime\rightarrow\gamma e^{+}e^{-}$,and the upper limits of the branching fractions as a function of the darkphoton are given at 90\% confidence level.

Improved measurements of the Dalitz decays $\eta/\eta'\rightarrow\gamma e^{+}e^{-}$