Bottomonium production associated with a photon at a high luminosity $e^+e^-$ collider with next-to-leading order QCD corrections

Abstract

We make a detailed discussion on the one-loop QCD correction to the bottomonium production associated with a photon, i.e. via the channel $e^{+}e^{-} \to\gamma^*/Z^0 \to |H_{b\bar{b}}\rangle + \gamma$, where $|H_{b\bar{b}}\rangle$ stands for the color-singlet bottomonium state as $\eta_b$, $\Upsilon$, $h_b$ or $\chi_{bJ}$ ($J$=0, 1 or 2), respectively. At the super $Z$ factory with the collision energy $E_{cm} \sim m_Z$, by summing up the cross sections for all bottomonium states, we obtain a large one-loop QCD correction, i.e. $|R|\sim 30\%$. This ensures the necessity and importance of the one-loop QCD corrections for the present processes. Further more, for the $\eta_b$, $h_b$ and $\chi_{bJ}$ production, their cross sections are dominated by the $s$-channel diagrams and are enhanced by the $Z^0$ boson resonance effect when $E_{cm}\sim m_Z$. While, for the $\Upsilon$ production, such resonance effect shall be smeared by a large $t(u)$-channel contribution that dominant over the $s$-channel one. Theoretical uncertainties caused by slight change of $E_{cm}$, the $b$-quark mass, the renormalization scale and etc. have been presented. At the super $Z$ factory with a high luminosity up to ${\cal L}=10^{36}{\rm cm}^{-2}{\rm s}^{-1}$, the bottomonium plus one photon events are sizable, especially for $\eta_b$ and $\Upsilon$, which have large signal significance. Summing up all bottomonium states, we shall totally have $\sim 3.8\times10^{5}$ bottomonium events in one operation year. So, the super $Z$ factory shall provide a good platform for studying the bottomonium properties.