Ambrosino, F (reprint author), Univ Naples Federico 2, Dipartimento Sci Fis, Naples, Italy.
We present a measurement of the ratio R=Gamma(K(e3 gamma)(0);E*(gamma) > 30 MeV, theta*(gamma)> 20 degrees)/Gamma(K(e3)(0)) and a first measurement of the direct emission contribution in semileptonic K(L) decays. The measurement was performed at the DA NE phi factory by selecting phi -> K(L)K(S) decays with the KLOE detector. We use 328 pb(-1) of data, corresponding to about 3.5 million K(e3)(0) events and about 9000 K(e3 gamma)(0) radiative events. Our result is R=(924 +/- 23(stat) +/- 16(syst))x10(-5) for the branching ratio and < X > = -2.3 +/- 1.3(stat) +/- 1.4(syst) for the effective strength parameter describing direct emission.