B* production in Z decays

Abreu, P. [--] Cortina Gil, Eduardo [UCL] DELPHI Collaboration [--] et al.

The decay /3* --* /3"7 has been observed with the DELPHI detector at LEP, where the /3* meson is produced in Z boson decays. The combination of inclusively reconstructed/3 mesons with well-measured converted photons yields a measurement of the flavour-averaged/3* -/3 mass difference of 45.5 4- 0.3 (stat.) -4- 0.8 (syst.) MeV/c 2. 95% confidence level upper limits at 6 MeV/c 2 are placed on both the isospin (i.e. B+-B ~ and the Bs-/3~d splitting of the mass difference. The production ratio of B* to B mesons in Z decays is measured to be 0.72 +0.03 (stat.) • (syst.). Limits on the production cross-section of other hypothetical excited B hadron states decaying radiatively are established. The differential/3* cross section has been measured to be in good agreement with the average b fragmentation, yielding an average fractional B* energy of (:rE) =0.695 • 0.009 (stat.) -I- 0.013 (syst.) . From the decay angular distribution the relative contribution of longitudinal t3" polarisation states is measured to be aLl(eL + ~rT) = 0.32 4- 0.04 (stat.) 4-0.03 (syst.).