Absence of zero field muon spin relaxation induced by superconductivity in the B phase of UPt3_3

We present muon spin relaxation measurements performed on crystals of the heavy fermion superconductor UPt$_3$. In zero applied field, contrary to a previous report, we do not observe an increase of the internal magnetic field in the lower superconducting phase (the B phase). Our result gives an experimental upper bound of the magnetic field that could be associated with the superconducting state.Comment: 4 pages, REVTeX 3.0, 2 PostScript figure