Observation of narrow baryon resonance decaying into $p{K}_s^0$ in pA-interactions at $70GeV/c$ with SVD-2 setup

Abstract

SVD-2 experiment data have been analyzed to search for an exotic baryon state, the ${\Theta }^{+}$-baryon, in a $p{K}_s^0$ decay mode at $70GeV/c$ on IHEP accelerator. The reaction $pA\to p{K}_s^0+X$ with a limited multiplicity was used in the analysis. The $p{K}_s^0$ invariant mass spectrum shows a resonant structure with $M=1526\pm 3(stat.)\pm 3(syst.)MeV/c^2$ and $\Gamma <24MeV/c^2$. The statistical significance of this peak was estimated to be of $5.6\sigma$. The mass and width of the resonance is compatible with the recently reported ${\Theta }^{+}$- baryon with positive strangeness which was predicted as an exotic pentaquark ($uudd\bar{s}$) baryon state. The total cross section for ${\Theta }^{+}$ production in pN-interactions for $X_F\ge 0$ was estimated to be $(30÷120)\mu b$ and no essential deviation from A-dependence for inelastic events $(\sim A^{0.7})$ was found.

8 pages, 7 figures, To be submitted to Yadernaya Fizika. v3-v5 - Some references added, minor typos corrected