OBSERVATION OF ORBITALLY EXCITED B-MESONS

Experimental evidence for the existence of orbitally excited B meson states is presented in an analysis of the B pi and B*pi distribution of Q = m(B**) - m(B(*)) - m(pi) using Z(0) decay data taken with the DELPHI detector at LEP. The mean Q-value of the decays B** --> B(*)pi is measured to be 284 +/-5 (stat.) +/- 15 (syst.) MeV/c(2), and the Gaussian width of the signal is 79 +/- 5 (stat.) +/- 8 (syst) MeV/c(2). This signal can be described as a single resonance of mass m = 5732+/-5 (stat.) +/- 20(syst.) MeV/c(2) and full width Gamma = 145 +/- 28 MeV/c(2). The observed shape is also consistent with the production of several broad and narrow states as predicted by the quark model and partly observed in the D-meson sector. The production rate of B** per b-jet is found to be 0.27 +/- 0.02(stat.) +/- 0.06 (syst.).