Kinetic Energy Flow in $\mathrm{Nb}\left(400A \mathrm{MeV}\right)+\mathrm{Nb}$: Evidence for Hydrodynamic Compression of Nuclear Matter

A kinetic-energy—flow analysis of multiplicity-selected collisions of ${}_{}{}^{93}{}_{}{}^{}\mathrm{Nb}(E_{\mathrm{lab}}=400A \mathrm{MeV})+{}_{}{}^{93}{}_{}{}^{}\mathrm{Nb}$ is performed on the basis of the nuclear fluid dynamical model. The effects of finite particle numbers on the flow tensor are explicitly taken into account. Strong sidewards peaks are predicted in $d\frac{N}{d}cos{\theta }_F$, the distribution of event by event flow angles. This is in qualitative agreement with recent data from the "Plastic Ball" electronic detection system. Cascade simulations fail to reproduce the data.