Nuclear-matter modification of decay widths in the $\ddot{I}•\to e^{+}{e}^{-}$ and $\ddot{I}•\to K^{+}{K}^{-}$ channels

Abstract

The invariant mass spectra of $\ddot{I}•\to K^{+}{K}^{-}$ are measured in 12 GeV $p+A$ reactions in order to search for the in-medium modification of $\ddot{I}•$ mesons. The observed $K^{+}{K}^{-}$ spectra are well reproduced by the relativistic Breit-Wigner function with a combinatorial background shape in three ${\hat{I}}^2{\hat{I}}^3$ 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 $\ddot{I}ƒ(A)=\ddot{I}{ƒ}_0\times A^{\hat{I}}\pm$ and obtain $\hat{I}{\pm }_{\ddot{I}•\to K^{+}{K}^{-}}-\hat{I}{\pm }_{\ddot{I}•\to e^{+}{e}^{-}}$ to be 0.14 $\pm$ 0.12. Limits are obtained for the partial decay widths of $\ddot{I}•$ mesons in nuclear matter.

5 pages, 4 figures