Study of the $pd\to ^3\textrm{He} K^+K^-$ and $pd\to ^3\textrm{He} ϕ$ reactions close to threshold

Abstract

Two--kaon production in proton--deuteron collisions has been studied at three energies close to threshold using a calibrated magnetic spectrograph to measure the final $^3$He and a vertex detector to measure the $K^+K^-$ pair. Differential and total cross sections are presented for the production of $ϕ$--mesons, decaying through $ϕ\to K^+K^-$, as well as for prompt $K^+K^-$ production. The prompt production seems to follow phase space in both its differential distributions and in its energy dependence. The amplitude for the $pd\to ^3${He}$ ϕ$ reaction varies little for excess energies below 22 MeV and the value is consistent with that obtained from a threshold measurement. The angular distribution of the $K^+K^-$ decay pair shows that near threshold the $ϕ$--mesons are dominantly produced with polarization $m=0$ along the initial proton direction. No conclusive evidence for $f_0(980)$ production is found in the data.