Measurement of the two-photon width of the. eta. and. eta. prime mesons

Formation of the {eta} and {eta}{prime} mesons in two-photon interactions has been observed with the ASP detector at the SLAC {ital e}{sup +}e{sup {minus}} storage ring PEP ({radical}{ital s}=29 GeV). In a data sample of 108 pb{sup {minus}1}, a total of 2287 {eta} and 547 {eta}{prime} events have been detected in the {gamma}{gamma} decay mode. The two-photon widths are determined to be {Gamma}{sub {gamma}{gamma}}({eta})=0.490{plus minus}0.010{plus minus}0.048 keV and {Gamma}{sub {gamma}{gamma}}({eta}{prime})=4.96{plus minus}0.23{plus minus}0.72 keV. The SU(3) pseudoscalar mixing angle deduced from these values is {theta}{sub {ital p}}={minus}19.8 {degree}{plus minus}2.2 {degree}.