Laser-driven optically-pumped Cs magnetometer array for a nEDM experiment

The Standard Model of Particle Physics predicts a static electric dipole moment for the neutron (nEDM) breaking time reversal and parity symmetry. This prediction is several orders of magnitude below the current best experimental limit dn < 2.9 . 10-26 ecm (90 % CL). We are currently setting up a new experiment at the new ultra-cold neutron (UCN) source at the Paul Scherrer Institut, Switzerland, with the ultimate goal to improve the sensitivity limit by almost two orders of magnitude. Besides passive and active compensation of external magnetic fields we will use an array of laser-driven optically-pumped atomic cesium magnetometers to control and monitor the stability and homogeneity of the magnetic field at the neutron precession chamber. A first array of eight cesium magnetometers was used to obtain the field distribution and stability over the neutron precession volume on a sub-pT level. The setup and first results are presented.