Search forΘ++Pentaquarks in the Exclusive Reactionγp→K+K−p

The reaction {gamma}p{yields}pK{sup +}K{sup -} was studied at Jefferson Lab with photon energies from 1.8 to 3.8 GeV using a tagged photon beam. The goal was to search for a {theta}{sup ++} pentaquark, a narrow, doubly charged baryon state having strangeness S=+1 and isospin I=1, in the pK{sup +} invariant mass spectrum. No statistically significant evidence of a {theta}{sup ++} was found. Upper limits on the total and differential cross section for the reaction {gamma}p{yields}K{sup -}{theta}{sup ++} were obtained in the mass range from 1.5 to 2.0 GeV/c{sup 2}, with an upper limit for a narrow resonance with a mass M{sub {theta}{sup ++}}=1.54 GeV/c{sup 2} of about 0.15 nb, 95% C.L.. This result places a stringent upper limit on the {theta}{sup ++} width {gamma}{sub {theta}{sup ++}}