Measurement of the spectroscopy of orbitally excited $B$ mesons with the L3 detector

We measure the mass, decay width and production rate of orbitally excited B mesons in 1.25 million hadronic Z decays registered by the L3 detector in 1994 and 1995. B meson candidates are inclusively reconstructed and combined with charged pions produced at the event primary vertex. An excess of events above the expected background is observed in the B\pi mass spectrum near 5.7 GeV. These events are interpreted as resulting from the decay B^** -> B^(*)pi, where B^** denotes a mixture of L=1 B meson spin states. The masses and decay widths of the B^*_2 (j_q = 3/2) and B^*_1 (j_q = 1/2) resonances and the relative production rate for the combination of all spin states are extracted from a fit to the mass spectrum.