Modification of the $\ddot{I}‰$-Meson Lifetime in Nuclear Matter

Abstract

The photo production of $\ddot{I}‰$ mesons on the nuclei C, Ca, Nb and Pb has been measured using the Crystal Barrel/TAPS detector at the ELSA tagged photon facility in Bonn. The dependence of the $\ddot{I}‰$ meson cross section on the nuclear mass number has been compared with three different types of models, a Glauber analysis, a BUU analysis of the Giessen theory group and a calculation by the Valencia theory group. In all three cases, the inelastic $\ddot{I}‰$ width is found to be $130-150MeV/{\mathrm{c}}^2$ at normal nuclear matter density for an average 3-momentum of 1.1 GeV/c. In the restframe of the $\ddot{I}‰$ meson, this inelastic $\ddot{I}‰$ width corresponds to a reduction of the $\ddot{I}‰$ lifetime by a factor $\approx 30$. For the first time, the momentum dependent $\ddot{I}‰$N cross section has been extracted from the experiment and is in the range of 70 mb.

5 pages, 4 figures