Search for the $\hat{I}{˜}^{+}$ pentaquark in the reactions ${\hat{I}}^{3}p\to {\bar{K}}^0{K}^{+}n$ and ${\hat{I}}^{3}p\to {\bar{K}}^0{K}^{0}p$

Abstract

The exclusive reactions ${\hat{I}}^{3}p\to {\bar{K}}^0{K}^{+}n$ and ${\hat{I}}^{3}p\to {\bar{K}}^0{K}^{0}p$ have been studied in the photon energy range 1.6--3.8 GeV, searching for evidence of the exotic baryon $\hat{I}{˜}^{+}(1540)$ in the decays $\hat{I}{˜}^{+}\to n{K}^{+}$ and $\hat{I}{˜}^{+}\to p{K}^0$. Data were collected with the CLAS detector at the Thomas Jefferson National Accelerator Facility. The integrated luminosity was about 70 pb${}^{-1}$. The reactions have been isolated by detecting the $K^{+}$ and proton directly, the neutral kaon via its decay to $K_S\to \ddot{I}{€}^{+}\ddot{I}{€}^{-}$ and the neutron or neutral kaon via the missing mass technique. The mass and width of known hyperons such as $\hat{I}{\pounds }^{+}$, $\hat{I}{\pounds }^{-}$ and $\hat{I}›(1116)$ were used as a check of the mass determination accuracy and experimental resolution. Approximately 100,000 $\hat{I}{›}^{\ast }(1520)$'s and 150,000 $\ddot{I}•$'s were observed in the ${\bar{K}}^0{K}^{+}n$ and ${\bar{K}}^0{K}^{0}p$ final state respectively. No evidence for the $\hat{I}{˜}^{+}$ pentaquark was found in the $n{K}^{+}$ or $p{K}_S$ invariant mass spectra. Upper limits were set on the production cross section of the reaction ${\hat{I}}^{3}p\to \hat{I}{˜}^{+}{\bar{K}}^0$ as functions of center-of-mass angle, $n{K}^{+}$ and $p{K}_S$ masses. Combining the results of the two reactions, the 95% C.L. upper limit on the total cross section for a resonance peaked at 1540 MeV was found to be 0.7 nb. Within most of the available theoretical models, this corresponds to an upper limit on the $\hat{I}{˜}^{+}$ width, $\hat{I}{“}_{\hat{I}{˜}^{+}}$, ranging between 0.01 and 7 MeV.

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