Search for the K-pp bound state via γd → K+π-X reaction at Eγ=1.5-2.4 GeV

A search for the K- pp bound state (the lightest kaonic nucleus) has been performed using the gamma d > K+pi X- reaction at E-gamma= 1.5-2.4 GeV at LEPS/SPring-8. The differential cross section of the K+pi(-) photo-production off deuterium (d(2)sigma/d cos theta(lab)(K+)/d cos theta(lab)(pi-)) has been measured for the first time in this energy region. A peak structure was searched for in the inclusive missing mass spectrum. A statistically significant peak structure was not observed in the region from 2.22 to 2.36 GeV/c(2). The upper limits of the differential cross section of the K- pp bound state production were determined to be (0.17-0.55), (0.55-1.7) and (1.1-2.9) mu b at 95% confidence level with the assumed widths of 20 MeV, 60 MeV and 100 MeV. (C) 2013 The Authors. Published by Elsevier B.V. All rights reserved,