In this paper, we present a comprehensive study of $Upsilon$ inclusive production in $Z$ boson decay, including the first complete next-to-leading-order calculations of the color-octet (CO) contributions. With the inclusion of the newly-calculated remarkable QCD corrections, the CO processes exhibit crucially phenomenological influence on the existing predictions built on the color-singlet mechanism. We also include the exhaustive evaluations of the feed-down contributions, which remained ignored in the literature, and find them to be considerable. Summing up all the contributions, the $mathcal{B}_{Z to Upsilon(nS)+X}$ still notably undershoot the data released by the L3 Collaboration.
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