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

Abstract

The associated production of a Z boson or an off-shell photon $γ^*$ with a bottom quark in the forward region is studied using proton-proton collisions at a centre-of-mass energy of $7\mathrm{Te}\mathrm{V}$. The Z bosons are reconstructed in the ${\text{Z}/γ^*}\!\rightarrow{μ^{+}μ^{-}}$ final state from muons with a transverse momentum larger than $20\mathrm{Ge}\mathrm{V}$, while two transverse momentum thresholds are considered for jets ($10\mathrm{Ge}\mathrm{V}$ and $20\mathrm{Ge}\mathrm{V}$). Both muons and jets are reconstructed in the pseudorapidity range $2.0<\hat{I}\cdot <4.5$. The results are based on data corresponding to $1.0{\,\mbox{fb}^{-1}}$ 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*} σ(\text{$\text{Z}/γ^*(μ^{+}μ^{-})$+b-jet}) = 295 \pm 60~(\text{stat}) \pm 51~(\text{syst}) \pm 10~(\text{lumi}) {\,\mbox{fb}} \end{equation*} for $p_{\mathrm{T}}$(jet)$>10\mathrm{Ge}\mathrm{V}$, and \begin{equation*} σ(\text{$\text{Z}/γ^*(μ^{+}μ^{-})$+b-jet}) = 128 \pm 36~(\text{stat}) \pm 22~(\text{syst}) \pm 5~(\text{lumi}) {\,\mbox{fb}} \end{equation*} for $p_{\mathrm{T}}$(jet)$>20\mathrm{Ge}\mathrm{V}$.