Experimental search for radiative decays of the pentaquark baryon Θ+(1540).

The data on the reactions K⁺Xe → K⁰ γX and K⁺Xe → K⁺ γX, obtained with the bubble chamber DIANA, have been analyzed for possible radiative decays of the Θ⁺(1540) baryon: Θ⁺ → K⁰ pγ and Θ⁺ → K⁺ nγ. No signals have been observed, and we derive the upper limits Γ(Θ⁺ → K⁰ pγ)/Γ(Θ⁺ → K⁰ p) < 0.032 and Γ(Θ⁺ → K⁺ nγ)/Γ(Θ⁺ → K⁺ nγ) < 0.041 which, using our previous measurement of Γ(Θ⁺ → KN) = 0.39 ± 0.10 MeV, translate to Γ(Θ⁺ → K⁰ pγ) < 8 keV and Γ(Θ⁺ → K⁺ nγ) < 11 keV at 90% confidence level. We have also measured the cross sections of K⁺-induced reactions involving emission of a neutral pion: σ( K⁺ n → K⁰ pπ⁰) = 68 ± 18 µb and σ( K⁺ N → K⁺ Nπ⁰) = 30 ± 8 µb for incident K⁺ momentum of 640 MeV. [ABSTRACT FROM AUTHOR]