Measurement of the B_s oscillation frequency via B_s mixing analyses provides
a powerful constraint on the CKM matrix elements. The study of B_d oscillations
is an important step towards B_s mixing and a preliminary measurement of Delta
m_d has been made with ~250 pb^-1 of data collected with the upgraded Run II D0
detector. Different flavor tagging algorithms have been developed and are being
optimized for use on a large set of B_s mesons that have been reconstructed in
different semileptonic decay modes.Comment: Poster presented at the XXIV Physics in Collisions Conference
(PIC04), Boston, USA, June 2004, 4 pages, LaTeX, 2 eps figure