Photoproduction of the K⁺K⁻(1750)

While photoproduction has often been advertised as an important environment in which to study light meson spectroscopy, solid experimental results are sparse. In fact, beyond the relatively straightforward photoproduction of the p, w, and ¢ mesons, the few results of exclusive photoproduction that do exist are poorly understood, and several, perhaps, have even been misinterpreted. After extensively reviewing the sometimes tenuous history of the exclusive photoproduction of the "p'(1600)," the "w1r0(1 2 50)," the "w(1650)," and the "K+ K-(1750)," new results from the E 8 31/FOCUS photoproduction experiment at Fermilab are presented which address the interpretation of the K+ K-(1750). This enhancement in low-PT K+ K- pairs at a mass near 1750 Me V / c2 has been observed by several previous photoproduction experiments, but, despite several apparent inconsistencies, it has always been interpreted as the JPC = 1 -- ¢(1680) meson. With nearly two orders of magnitude more events than any previous observation of the K+ K-(1750), and based on precise measurements of its mass and width, and its absence from the K* K final state, the FOCUS data can finally render this interpretation implausible. In addition, several steps have been taken towards establishing a new interpretation. Based on limited angular analyses of its decay and the beam energy dependence of its production, we argue that, in the absence of any wild interference scenarios, the K+ K-(1 750) has JPC # 1--, and, in fact, the most likely assignment appears to be 2 ++ . It is hoped that this work can help set the stage for future reevaluations and new insights in photoproduction.