The reaction e+e~e+e m. m has been analyzed using 97 pb ' of data taken with the Crystal Ball detector at the DESY e e+ storage ring DORIS II at beam energies around 5.3 GeV. For the first time we have measured the cross section for yy~m. m. for n m invariant masses ranging from threshold to about 2 GeV. We measure an approximately flat cross section of about 10 nb for 8'=m 0 0 (0.8 GeV, which is below 0.6 GeV, in good agreement with a theoretical prediction 'tr n' based on an unitarized Born-term model. At higher invariant masses we observe formation of the ft(1270) resonance and a hint of the fo(975). We deduce the following two-photon widths: I rr(f, (1270)) =3.19+0. 1620 z, keV and I "(fo( 975)) (0.53 keV at 90% CL. The decayangular distributions show the m~system to be dominantly spin 0 for W &0.7 GeV and spin 2, helicity 2 in the f, (1270) region, with helicity 0 contributing at most 22% (90% C.L.).

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We report on measurements of the shift in resonance frequency of “spoof” surface plasmon polariton propagation along a 2-D metamaterial slow-wave structure induced by a gaseous plasma near the metamaterial/air interface. A transmission line circuit model for the metamaterial structure interprets the introduction of a plasma as a decrease in unit cell capacitance, causing a shift in the plasmon dispersion to higher frequency. We show through simulations and experiments that the effects of this shift at the resonance frequency and attenuation below and above resonance depend on the plasma density. The shifts recorded experimentally are small owing to the low plasma densities generated near the structure, ∼1011 cm−3, but simulations show that a shift of ∼3% of the resonance frequency can be generated at plasma densities of ∼1012 cm−3.

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Using the Crystal Ball detector at the DORIS II e+e-storage ring, we measure the TIn°n ° mass spectrum in the reaction e+e-*e+e-Tln°n°-~e+e-6T from the "qn°n ° threshold to about 2500 MeV/c 2. The spectrum is dominated by the 11' , for which we determine/'w0]')BR (q' ~6y) = 0.36 +_ 0.02 + 0.03 keV. In addition, we observe an enhancement in the cross section near 1900 MeV/c 2 which we attribute to the two-photon production of a new resonance X (1900). The angular distributions and the invariant mass distribution of the Tin ° subsystem are consistent with those expected for the hypothetical ~12 meson with jec= 2-+. For this je assignment the resonance parameters are M(X) = 1876 + 35 + 50 MeV/c 2, /'tot(X) =228 + 90_+ 34 MeV/c 2 and Frr(X)BR(X-,Ilnn) =0.9+0.2+0.3 keV.