Positive muon Knight shift and spin relaxation in heavy fermion superconductors UPt3 and UBe13

We report muon spin rotation/relaxation (μSR) measurements of the heavy fermion superconductors UBe13 and UPt3. In both materials we find that the muon Knight shift is unchanged in the superconducting state, consistent with odd-parity pairing (such as p-wave). The magnetic field penetration depths in UPt3 and UBe13 are extremely long, greater than 10000 Å. We find no evidence of a magnetic transition in UBe13 below 10 K.