Recent Results on Searches for Pentaquark States from STAR at RHIC

Abstract

We present results on pentaquark searches from nuclear collisions at RHIC with the STAR detector system. An intriguing peak has been observed in the invariant mass distribution of $p{K}^{+}+\overline{p}{K}^{-}$ from 18.6 Million d+Au collision events at $\sqrt{s_{{}_{NN}}}=200$~GeV. The peak centers at a mass $1528\pm 2\pm 5$~MeV/c${}^2$ and the FWHM $\sim 15$ MeV/c${}^2$ limited by detector responses. The statistical significance of the peak is $4.2\sigma$. Such a state if confirmed is manifestly exotic and implies a family of isospin one states. A weak signal of less statistical significance ($\sim 3\sigma$) has been observed in 5.6M Au+Au collision events at 62.4 GeV. Searches in 10.7M Au+Au collision events at 200 GeV yield no significant signal. The Au+Au results neither confirm nor rule out the d+Au observation as a possible state.

To appear in proceedings of International Conference on QCD and Hadron Physics at Beijing, June 2005

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• Present status on experimental search for pentaquarks
• Search for ${\Theta }^{++}$ Pentaquarks in the Exclusive Reaction $\gamma p\to K^{+}{K}^{-}p$
• Positive parity pentaquark towers in large Nc QCD
• The 27-plet baryons with spin 3/2 under SU(3) symmetry