Photoproduction of the doubly-strange Ξ hyperons

Abstract We report on the first measurement of exclusive Ξ − and Ξ 0 photoproduction. The Ξ − states are produced in the reaction γ p → K + K + Ξ − , and the Ξ 0 states in γ p → K + K + π − Ξ 0 . Identification is made by the unique mass measured as the missing mass of the K + K + (or K + K + π − ) system using the CLAS detector at the Thomas Jefferson National Accelerator Facility. A systematic study of the excited Ξ spectrum improves our understanding of the N ∗ and Δ ∗ states, since the Ξ ∗ states are related to them by SU ( 3 ) flavor symmetry. At the highest energies available at Jefferson Lab, we begin to find evidence for known excited Ξ − states in the photoproduction process, and possibly new states at 1770 and 1860 MeV, although we do not have enough statistics to draw a strong conclusion. A search for the Ξ 5 − − ( 1862 ) pentaquark state seen by NA49 is made using the process γ p → K + K + π + X , but the result is inconclusive for lack of statistics.