V. V. Molchanov

Search forN ϕ (1960) baryon

In the experiments at the SPHINX facility in the 70 GeV proton beam of the IHEP accelerator the diffractive production reactionsp+N→[Σ(1385)0K+] +N andp+N→[Σ(1385)0K+]+N+ (neutral particles) were studied. In the effective mass spectra of the [Σ(1385)0K+] system in these processes there were no signals from the anomalously narrow baryon stateNϕ (1960) which had been observed earlier in the measurement at the BIS-2 setup.

Study of coherent diffractive production reactions ofp+C→[Y0K+]+C type and observation of narrow structures in ∑ (1385)0K+ and ∑0K+ effective mass spectra

In the experiments at the SPHINX facility in 70 GeV proton beam of the IHEP accelerator the coherent diffractive production reactions on carbon nucleip+C→ [∑(1385)0K++C andp+C→[Σ0K+]+C were investigated. The evidences for new baryon states were obtained in the study of hyperon-kaon effective mass spectra in these two reactions:X (2050) with massM=(2052±6) MeV and width Γ=(35−35+22) MeV inM[∑(1385)0K+] andX(2000) withM=1999±6 MeV and Γ=91±17 MeV inM[Σ0K+]. The unusual features of these massive states (small enough decay widths, anomalously large branching ratios for decays with strange particles emission) make them very serious candidates for cryptoexotic pentaquark baryons with hidden strangeness.

Investigation of the diffractive reaction p + N → [∑+ K 0] + N at the proton energy of E p =70 GeV and observation of the decay process X(2000) → ∑+ K 0

The diffractive reaction p + N → [∑+K0] + N induced by 70-GeV protons is investigated at the SPHINX facility. The measured mass spectrum of the ∑+K0 system originating from this reaction shows a resonance structure with a mass of M=1995±18 MeV and a width of Γ=90±32 MeV. The cross section for the formation of this structure is found to be σ=182±38 nb per target nucleon. These data comply well with the results that we obtained previously in studying the reaction p + N → [∑0K+] + N, where we observed the formation of the X(2000) → ∑0K+ state, a candidate for an exotic baryon with hidden strangeness. The measured ratio R of the two branching fractions, R = Br[X(2000) → ∑+K0]/Br[X(2000) → ∑0K+] = 1.91 ± 0.38, is consistent with the value of R=2 expected for an isospin-1/2 baryon.

Study of the diffractive production of baryon states and search for cryptoexotic baryons with hidden strangeness

The reactions of baryon diffractive productionp+N→(pK+K−)+N, p+N→(pϕ)+N, p+N→[Λ(1520)K+]+N p+N→[Σ(1385)oK+]+N in the 70 GeV proton beam were studied. Very sensitive upper limits for the production cross sections of heavy narrow cryptoexotic baryon resonances with hidden strangeness were obtained.