Observation of orbitally excitedBmesons inpp¯collisions ats=1.8 TeV

We measure the relative rate of production of orbitally excited (L = 1) states of B mesons (B**) by observing their decays into B pi (+/-). We reconstruct B mesons through semileptonic decay channels using data collected in p(p) over bar collisions at roots = 1.8 TeV. The fraction of light B mesons that are produced as L = 1B** states is measured to be 0.28 +/- 0.06(stat) +/- 0.03(syst). We also measure the collective mass of the B** states, and quantify the result by quoting the (model-dependent) mass of the lowest B** state to be m(B-1) = 5.71 +/- 0.02 GeV/c(2).