Strength of intermediate-range forces coupling to isospin.

An experimental search for new forces coupling to nuclear isospin with a range of {ge}3 m was conducted using a torsion balance driven in resonance by a set of masses configured to generate a nearly pure isospin source field. The strength of any such coupling {xi} in units of gravity per atomic mass unit is found to be bounded by {minus}2.3{times}10{sup {minus}4}{le}{xi}{le}+2.7{times}10{sup {minus}5}, where the positive sign represents an attractive force between like isospin charges.