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Title: Observation of an Exotic Baryon with S=+1 in Photoproduction from the Proton

The reaction {gamma}p {yields} {pi}{sup +} K{sup -} K{sup +}n was studied 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 {+-} 10 MeV/c{sup 2} was observed in the nK{sup +} invariant mass spectrum. The peak's width is consistent with the CLAS resolution (FWHM = 26 MeV/c{sup 2}), and its statistical significance is 7.8 {+-} 1.0 {sigma}. A baryon with positive strangeness has exotic structure and cannot be described in the framework of the naive constituent quark model. The mass of the observed state is consistent with the mass predicted by a chiral soliton model for the {Theta}{sup +} baryon. In addition, the pK{sup +} invariant mass distribution was analyzed in the reaction {gamma} p {yields} K{sup -} K{sup +}p with high statistics in search of doubly-charged exotic baryon states. No resonance structures were found in this spectrum.
Authors:
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Publication Date:
OSTI Identifier:
836840
Report Number(s):
JLAB-PHY-03-203; DOE/ER/40150-3139; hep-ex/0311046
Journal ID: ISSN 0031-9007; PRLTAO; TRN: US0500811
DOE Contract Number:
AC05-84ER40150
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review Letters; Journal Volume: 92; Other Information: PBD: 1 Jan 2004
Research Org:
Thomas Jefferson National Accelerator Facility, Newport News, VA (US)
Sponsoring Org:
US Department of Energy; USDOE Office of Energy Research (ER) (US)
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; BARYONS; ENERGY RANGE; MASS DISTRIBUTION; PHOTON BEAMS; PHOTOPRODUCTION; PROTONS; QUARK MODEL; RESOLUTION; RESONANCE; SOLITONS; STATISTICS; STRANGENESS