The polarization-asymmetry correlation of107In and parity violation

We report on the first measurements of the longitudinal polarization of positrons emitted by polarized nuclei, using cryogenically polarized¹⁰⁷In. This so-called polarization-asymmetry correlation is very sensitive to the mass of a possible right-handed gauge boson, which is invoked by parity symmetric extensions of the standard V-A electroweak model to explain the experimentally observed strong violation of parity which, however, may not be complete. The positron polarization is deduced from the time-resolved decay spectrum of positronium hyperfine states. Our preliminary result points to a lower limit of about 210 GeV for the mass of an eventual right-handed charged W gauge boson. This result can still be improved.