B * production in Z decays

The decayB*→Bγ has been observed with the DELPHI detector at LEP, where theB* meson is produced inZ boson decays. The combination of inclusively reconstructedB mesons with well-measured converted photons yields a measurement of the flavour-averagedB*-B mass difference of 45.5±0.3 (stat.) ±0.8 (syst.) MeV/c2. 95% confidence level upper limits at 6 MeV/c2 are placed on both the isospin (i.e.B+-B0) and theB s -B ud splitting of the mass difference. The production ratio ofB* toB mesons inZ decays is measured to be 0.72±0.03 (stat.) ±0.06 (syst.). Limits on the production cross-section of other hypothetical excitedB hadron states decaying radiatively are established. The differentialB* cross section has been measured to be in good agreement with the averageb fragmentation, yielding an average fractionalB* energy of 〈x E 〉=0.695±0.009 (stat.) ±0.013 (syst.). From the decay angular distribution the relative contribution of longitudinalB* polarisation states is measured to be σL/(σL + σT) = 0.32 ± 0.04 (stat.) ±0.03 (syst.).