Search for S=+1 exotic baryon in γp→π<sup>+</sup>K<sup>-</sup>K<sup>+</sup>n
Guo, Lei
:
2004-04-14
Abstract
<font size=+1> The reaction γ p →
π<sup>+</sup> K<sup>-</sup>K<sup>+</sup>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/c<sup>2</sup> was observed in the (nK<sup>+</sup>)invariant mass
spectrum. The width of the peak is consistent with the CLAS resolution
(FWHM=26~MeV/c<sup>2</sup> ), 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<sup>-</sup>, 1<sup>-</sup> and 1<sup>+</sup>
partial wave intensity distributions. Due to the low statistics, the resonant
nature of these meson waves is not determined.</font>