Pairing-Symmetry Selection Rules for the Cooper-Pair Mass Anomaly from A5 Microsector Representation Theory

The Cooper-pair mass in niobium, measured by Tate et al. (1989) via the London moment, exceeds twice the free-electron mass by δ = 92 ± 21 ppm — a 4.4σ anomaly unexplained for 36 years. Working within the A5 microsector of Density Field Dynamics (DFD), we establish three results at decreasing levels of rigor. First (exact within the pair-space construction): two pairing-symmetry selection rules. (a) An angular-cancellation rule: the quintet exchange channel in S²(V*) = 1 ⊕ 5 couples maximally to s-wave condensates but vanishes for d-wave condensates, whose sign-changing gap produces destructive interference. (b) An orthogonality rule: spin-triplet pairs live in Λ²(V*) = 3, which is orthogonal to the quintet by representation theory alone, independent of gap structure. Second (mechanism conjecture): the physical Cooper pair carries quintet weight 2/3, accessing an exchange channel unavailable to uncorrelated single electrons, at the natural scale O(α²). Third (numerical conjecture): a motivated coefficient δ = √3 α² = 92.23 ppm, with √3 from the three-generation structure of CP² × S³. The match to Tate's measurement is 0.01σ with zero free parameters. Unlike the BCS-exchange correction of Lipavský (2016), which is material-dependent, the framework predicts universality for conventional s-wave superconductors — a distinction testable with existing London-moment technology. Sharp falsifier: if δ varies across s-wave materials tracking Δ/E_F, the framework is ruled out.