Measurement of Inclusive $f_1(1285)$ and $f_1(1420)$ Production in $Z$ Decays with the DELPHI Detector

Inclusive production of two $(K\bar K\pi)^0$ states in the mass region 1.22--1.56 GeV in $Z$ decay at LEP I has been observed by the DELPHI Collaboration. The measured masses and widths are $1274\pm4$ and $29\pm12$ MeV for the first peak and $1426\pm4$ and $51\pm14$ MeV for the second. A partial-wave analysis has been performed on the $(K\bar K\pi)^0$ spectrum in this mass range; the first peak is consistent with the quantum numbers $I^G(J^{PC})=0^+(0^{-+}/1^{++})$ and the second with $I^G(J^{PC})=0^+(1^{++})$. These measurements, as well as their total hadronic production rates per hadronic $Z$ decay, are consistent with the mesons of the type $n\bar n$, where $n=\{u,d\}$. They are very likely to be the $f_1(1285)$ and the $f_1(1420)$, respectively.