Recent results on hadron spectroscopy are reported, with special emphasis on the evidence for a narrow baryonic state decaying to K_S~0p and K_S~0p, compatible with the pentaquark state, Θ~+, observed by fixed-target experiments. The data were collected with the ZEUS detector at HERA using an integrated luminosity of 121 pb~(-1). The analyses were performed in the central rapidity region of inclusive deep inelastic scattering at an ep center-of-mass energy of 300-318 GeV. Evidence for a narrow resonance in the K_S~0p and K_S~0p invariant mass spectrum is obtained, with mass 1521.5 ± 1.5(stat)_(-1.7)~(+2.8)(syst) MeV and width consistent with the experimental resolution. If the K_S~0p part of the signal is identified with the strange pentaquark Θ~+, the K_S~0p part is the first evidence for its antiparticle, Θ~-.Also reported are cross-section measurements for Θ~+ production and decay. The cross sections are compared in bins of Q_(min)~2 to those of A-baryons produced in the same kinematic region. Supporting results on other hadron resonances are also discussed.
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