Tests for coherence in neutral B meson decays - art. no. 054006

A density-matrix method for the study of tagged states of neutral B masons with arbitrary coherence properties is applied to several examples, includi ng e(+) e(-) production, both at and above the Y(4S) resonance, and hadroni c production. In the absence of coherence the only term modulating the expo nential decay of a neutral B mason behaves as cos Delta mt, while a sin Del ta mt modulation is a signal of partial or full coherence. Decays to CP eig enstates ale needed to fully specify the density matrix. We relate these re sults to more familiar expressions far the cases of the Y(4S) and incoheren t production.