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Title page for ETD etd-04082004-234959


Type of Document Dissertation
Author Guo, Lei
Author's Email Address lguo@jlab.org
URN etd-04082004-234959
Title Search for S=+1 exotic baryon in γp→π+K-K+n
Degree PhD
Department Physics
Advisory Committee
Advisor Name Title
David J. Ernst Committee Chair
Sait A. Umar Committee Member
Dennis P. Weygand Committee Member
Medford S. Webster Committee Member
Paul D. Sheldon Committee Member
Senta V. Greene Committee Member
Thomas W. Kephart Committee Member
Keywords
  • PWA
  • exotic
  • photoproduction
  • hadron spectroscopy
  • Jefferson Lab
  • CLAS
  • pentaquark
Date of Defense 2004-04-05
Availability unrestricted
Abstract
      The reaction γ p →

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 &sigma. 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.

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