Results from the Y(5S) engineering run (BELLE)

Abstract

We report results based on a 1.86 fb$^{-1}$ data sample collected on the $Υ$(5S) resonance by the Belle detector at the KEKB asymmetric energy $e^+ e^-$ collider. The inclusive production of $D_s$, $D^0$ and $J/ψ$ mesons at the $Υ$(5S) is studied. From the $D_s$ inclusive branching fraction the ratio $f_s = (16.4 \pm 1.4 \pm 4.1)%$ of $B_s^{(*)} \bar{B}_s^{(*)}$ to the total $b\bar{b}$ quark pair production at the $Υ$(5S) energy is obtained in a model dependent way. The exclusive decays $B_s \to D_s^{(*)+} π^- (/ρ^-)$ and $B_s \to J/Ψϕ(/η)$ are studied and a significant $B_s$ signal is observed combining these modes. The $B_s$ meson production is found to proceed predominantly through the creation of $B^*_s \bar{B}^*_s$ pairs. Upper limits on $B_s \to K^+ K^-$, $B_s \to ϕγ$, $B_s \to γγ$ and $B_s \to D_s^{(*)+} D_s^{(*)-}$ decays are reported.