Search for pentaquark partners [Theta]⁺⁺, [Sigma]⁰ and N⁰ in H (e,e'K [pi])) X reactions at Jefferson Lab Hall A

Abstract

In 1997, D. Diakonov et al. using a soliton model predicted a SU(3)F flavor antide-cuplet of pentaquarks. The most striking prediction using this symmetry group is a narrow exotic state, E+(1540), which has quark component uuddg. If such a state is confirmed, other members of the antide cuplet could be expected to have sufficiently narrow widths to be observed as well. The Jefferson Laboratory experiment E04-012 focused on the search for EO and NO partner states in the missing mass spectra of the H(e,e'K+)X and H(e,e'ir+)X channels. In addition, if the 8+ has non-zero isospin then a hypothetical isospin partner, O++, might be expected in the H(e,e'K-)X channel; this was also investigated. The experiment was performed in Hall A at Jefferson Lab using a 5 GeV electron beam incident on a liquid hydrogen target. The two high resolution magnetic spectrometers were coupled to septum magnets to allow measurement of scattered electrons and outgoing hadrons at angles as small as 6 degrees. The missing mass resolution was determined to be 3.5 MeV/c2 FWHM using neutron, A(1116) and E(1193) production and provided a high sensitivity to narrow resonances. A precise measurement of the A(1520) resonance has also been conducted for a cross-section comparison. As a result, no significant narrow resonances were observed in any of the three reaction channels being investigated. Based on this fact, a likelihood scan using the G. Feldman and R. Cousins method was performed. The analysis provided total cross section upper limits at 90% confidence level with no lower limits or always below background fluctuation.