The positive-strangeness baryon resonance + is observed in photoproduction of the nK + K 0 s final state with the SAPHIR detector at the Bonn ELectron Stretcher Accelerator ELSA. It is seen as a peak in the nK + invariant mass distribution with a 4.8σ confidence level. We find a mass M + = 1540 ± 4 ± 2 MeV and an upper limit of the width Γ + < 25 MeV at 90% c.l. The photoproduction cross section for K 0 + is in the order of 300 nb. From the absence of a signal in the pK + invariant mass distribution in γ p → pK + K − at the expected strength we conclude that the + must be isoscalar.

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