Measurement of the in-medium ϕ-meson width in proton-nucleus collisions

The production of ϕ mesons in the collisions of 2.83 GeV protons with C, Cu, Ag, and Au at forward angles has been measured via the ϕ→K+K− decay using the COSY-ANKE magnetic spectrometer. The ϕ meson production cross section follows a target mass dependence of A0.56±0.03 in the momentum region of 0.6-1.6 GeV/c. The comparison of the data with model calculations suggests that the in-medium ϕ width is about an order of magnitude larger than its free value.