Hyperfine splitting ofBmesons andBsproduction at the Υ(5S)

Abstract

Using the Columbia University–Stony Brook (CUSB-II) detector we have studied the inclusive photon spectrum from 2.9×${10}^4$ Υ(5S) decays. We observe a strong signal due to ${\mathit{B}}^{\mathrm{*}}$→Bγ decays. From this we obtain (i) the average ${\mathit{B}}^{\mathrm{*}}$-B mass difference, 46.7±0.4 MeV, (ii) the photon yield per Υ(5S) decay, 〈γ/Υ(5S)〉=1.09±0.06, and (iii) the average velocity of the ${\mathit{B}}^{\mathrm{*}}$’s, 〈β〉=0.156±0.010, for a mix of nonstrange (B) and strange (${\mathit{B}}_{\mathit{s}}$) ${\mathit{B}}^{\mathrm{*}}$ mesons from Υ(5S) decays. From the shape of the photon line, we find that both B and ${\mathit{B}}_{\mathit{s}}$ mesons are produced with nearly equal values for the hyperfine splitting of the B and ${\mathit{B}}_{\mathit{s}}$ meson systems.