Noncyclic Pancharatnam phase for mixed state SU(2) evolution in neutron polarimetry

We have measured the Pancharatnam relative phase for spin-1/2 states. In a neutron polarimetry experiment the minima and maxima of intensity modulations, giving the Pancharatnam phase, were determined. We also considered general SU(2) evolution for mixed states. The results are in good agreement with theory.