First Measurement of the Electromagnetic Form Factor of the Neutral Kaon at a Large Momentum Transfer and the Effect of $SU(3)$ Breaking

Abstract

At large momentum transfers the photon interacts with the charges and spins of the constituent partons in a hadron. It is expected that the neutral kaon can acquire finite electromagnetic form factors because its wave function is affected by the order of magnitude difference between the mass of the strange quark and that of the down quark, or flavor $SU(3)$ breaking. We report on the first measurement of the form factor of neutral kaons at the large timelike momentum transfer of $|Q^2|=17.4$ GeV${}^2$ by measuring the cross section for $e^{+}{e}^{-}\to K_S{K}_L$ at $\sqrt{s}=4.17$ GeV using CLEO-c data with an integrated luminosity of 586 pb${}^{-1}$. We obtain $F_{K_S{K}_L}(17.4{\text{GeV}}^2)=5.3\times 10^{-3}$, with a 90% C.L. interval of $(2.9-8.2)\times 10^{-3}$. This is nearly an order of magnitude smaller than $F_{K^{+}{K}^{-}}(17.4{\text{GeV}}^2)=(44\pm 1)\times 10^{-3}$, and indicates that the effect of $SU(3)$ breaking is small. In turn, this makes it unlikely that the recently observed strong violation of the pQCD prediction, $F_{{\pi }^{+}{\pi }^{-}}(|Q^2|)/F_{K^{+}{K}^{-}}(|Q^2|)=f_{\pi }^2/f_K^2$, which is based on the assumption of similar wave functions for the pions and kaons, can be attributed to $SU(3)$ breaking alone.

4 pages, 2 figures, accepted to PLB

References in corpus (2)

• Moments of pseudoscalar meson distribution amplitudes from the lattice
• Experimental Study of the Reaction $e^{+}{e}^{-}\to K_S{K}_L$ in the Energy Range $\sqrt{s}=1.04÷1.38$ GeV

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• Exposing strangeness: projections for kaon electromagnetic form factors
• Flavour symmetry breaking in the kaon parton distribution amplitude
• Study of the $e^{+}{e}^{-}\to K^{+}{K}^{-}$ reaction in the energy range from 2.6 to 8.0 GeV
• Evidence for the decay $\psi (3770)\to K^{+}{K}^{-}$