Nuclear-Matter Modification of Decay Widths in the $\ensuremath{\phi}\ensuremath{\rightarrow}{e}^{+}{e}^{\ensuremath{-}}$ and $\ensuremath{\phi}\ensuremath{\rightarrow}{K}^{+}{K}^{\ensuremath{-}}$ Channels

Nuclear-Matter Modification of Decay Widths in the $ϕ \to e^{+} e^{-}$ and $ϕ \to K^{+} K^{-}$ Channels

F. Sakuma et al. (KEK-PS E325 Collaboration)

Phys. Rev. Lett. 98, 152302 – Published 13 April 2007

Abstract

The invariant mass spectra of $ϕ \to K^{+} K^{-}$ are measured in 12 GeV $p + A$ reactions in order to search for the in-medium modification of $ϕ$ mesons. The observed $K^{+} K^{-}$ spectra are well reproduced by the relativistic Breit-Wigner function with a combinatorial background shape in three $β γ$ regions between 1.0 and 3.5. The nuclear mass number dependence of the yields of the $K^{+} K^{-}$ decay channel is compared to the simultaneously measured $e^{+} e^{-}$ decay channel for carbon and copper targets. We parameterize the production yields as $σ (A) = σ_{0} A^{α}$ and obtain $α_{ϕ \to K^{+} K^{-}} - α_{ϕ \to e^{+} e^{-}}$ to be $0.14 \pm 0.12$ . Limits are obtained for the partial decay widths of the $ϕ$ mesons in nuclear matter.