Nuclear-Matter Modification Of Decay Widths In The Phi -> E(+)E(-) And Phi -> K+K- Channels

The invariant mass spectra of phi -> K+ K- are measured in 12 GeV p + A reactions in order to search for the in-medium modification of phi mesons. The observed K+ K- spectra are well reproduced by the relativistic Breit-Wigner function with a combinatorial background shape in three beta gamma 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 sigma(A) = sigma(0)A(alpha) and obtain alpha(phi -> K+K-) - alpha(phi -> e+e-) to be 0: 14 +/- 0: 12. Limits are obtained for the partial decay widths of the phi mesons in nuclear matter.