Search for S=+1 exotic baryon in γp→π⁺K^-K⁺n

Abstract

<font size=+1> The reaction γ p &rarr; π⁺ K^-K⁺n has been investigated at Jefferson Lab using a tagged photon beam with an energy range of 3-5.47 GeV. A narrow baryon state with strangeness S=+1 and mass M=1555±; 7±; 10 MeV/c² was observed in the (nK⁺)invariant mass spectrum. The width of the peak is consistent with the CLAS resolution (FWHM=26~MeV/c² ), and its statistical significance is 7.8 ±; 1.0 σ. A baryon with positive strangeness has necessarily exotic structure and cannot be described in the framework of the naive constituent quark model. The signal is consistent with that predicted by a chiral soliton model for a 5-quark baryon state. Partial Wave Analysis was performed for the three-body mesonic background with the photon energy range of 4.8-5.47 GeV . The analysis demonstrates that the observed signal is unlikely to arise from meson production in the same final state. Interesting features were also observed in the 2^-, 1^- and 1⁺ partial wave intensity distributions. Due to the low statistics, the resonant nature of these meson waves is not determined.</font>