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

The data on the reactions K +Xe → K 0 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+ → K 0 pγ and Θ+ → K + nγ. No signals have been observed, and we derive the upper limits Γ(Θ+ → K 0 pγ)/Γ(Θ+ → K 0 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+ → K 0 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 → K 0 pπ 0) = 68 ± 18 µb and σ(K + N → K + Nπ 0) = 30 ± 8 µb for incident K + momentum of 640 MeV.