STUDY OF DIFFRACTIVE PRODUCTION PROCESSES IN PROTON-NUCLEON AND PROTON-NUCLEUS INTERACTIONS AND SEARCH FOR EXOTIC BARYONS

Coherent diffractive production reactions p + C --> [Sigma(1385)K-0(+) ] + C and p + C --> [Sigma(0)K(+)] + C on carbon nuclei were investiga ted in experiments at the SPHINX facility in a 70-GeV proton beam from the IHEP accelerator. A large body of evidence for new baryon states was obtained in the study of hyperon-kaon effective-mass spectra in th ese two reactions: X(2050) with mass M = 2052 +/- 6 MeV and width Gamm a = 35(-35)(+22) MeV in M[Sigma(1385)K-0(+)] and X(2000) with M = 1999 +/- 6 MeV and Gamma = 91 +/- 17 MeV in M[Sigma(0)K(+)]. The unusual f eatures of these massive states (comparatively small decay widths and anomalously large branching ratios for decays with strange-particle em ission) make them very serious candidates for cryptoexotic pentaquark baryons with hidden strangeness. Preliminary data on the reactions p N --> [p eta] + N and p + N --> [p eta'] + N, as well as first result s for M[Sigma(0)K(+)], M(p eta'), and M(p eta') effective mass spectra in nonperipheral region (with p(T)(2) > 0.3 GeV2), are presented.