Measurement of the Z+b-jet cross-section in pp collisions at $\sqrt{s}=7\mathrm{T}\mathrm{e}\mathrm{V}$ in the forward region

The associated production of a Z boson or an off-shell photon ${\gamma }^{\ast }$ with a bottom quark in the forward region is studied using proton-proton collisions at a centre-of-mass energy of $7\mathrm{T}\mathrm{e}\mathrm{V}$. The Z bosons are reconstructed in the $\text{Z}\mathrm{/}{\gamma }^{\ast }\text{\hspace{0.17em}⁣}\to {\mu }^{+}{\mu }^{-}$ final state from muons with a transverse momentum larger than $20\mathrm{G}\mathrm{e}\mathrm{V}$, while two transverse momentum thresholds are considered for jets ($10\mathrm{G}\mathrm{e}\mathrm{V}$ and $20\mathrm{G}\mathrm{e}\mathrm{V}$). Both muons and jets are reconstructed in the pseudorapidity range $2.0<\eta <4.5$. The results are based on data corresponding to $1.0f{b}^{-1}$ recorded in 2011 with the LHCb detector. The measurement of the Z+b-jet cross-section is normalized to the Z+jet cross-section. The measured cross-sections are \begin{equation*} \sigma($\text{Z}\mathrm{/}{\gamma }^{\ast }({\mu }^{+}{\mu }^{-})\text{+b-jet}$) = 295 \pm 60~($\text{stat}$) \pm 51~($\text{syst}$) \pm 10~($\text{lumi}$) {,\mbox{fb}} \end{equation*} for $p_{\mathrm{T}}$(jet)$>10\mathrm{G}\mathrm{e}\mathrm{V}$, and \begin{equation*} \sigma($\text{Z}\mathrm{/}{\gamma }^{\ast }({\mu }^{+}{\mu }^{-})\text{+b-jet}$) = 128 \pm 36~($\text{stat}$) \pm 22~($\text{syst}$) \pm 5~($\text{lumi}$) {,\mbox{fb}} \end{equation*} for $p_{\mathrm{T}}$(jet)$>20\mathrm{G}\mathrm{e}\mathrm{V}$.