  The new antiferromagnetic (AF) compound BaCu_2Si_2O_7 is studied by magnetic
susceptibility and neutron scattering techniques. The observed behavior is
dominated by the presence of loosely coupled S=1/2 chains with the intrachain
AF exchange constant J = 24.1 meV. Long-range Neel ordering is observed below
Tn = 9.2 K. The results are discussed within the framework of the Mean
Field-RPA model for weakly interacting quantum spin chains.
