Measurement of jet production in $Z^0/\gamma^*\rightarrow\mu^+\mu^-$ events at LHCb in $\sqrt s = 7$ TeV pp collisions

The first LHCb measurement of $Z^0/\gamma^*$ + jet production is presented. This measurement is performed in the $Z^0/\gamma^*\rightarrow\mu^+\mu^-$ channel, and is normalised to the total inclusive $Z^0/\gamma^*\rightarrow\mu^+\mu^-$ cross-section, based on $1.02\pm0.04$ fb$^{-1}$ of data collected in 2011. The results are given for a fiducial acceptance inside the LHCb acceptance, defined as $2.0~\le~\eta(\mu)~\le~4.5$, $p_\text{T}(\mu)~\ge~20$ GeV, and with the reconstructed dimuon mass in the range $60~\le~M~\le~120$ GeV. Jets are reconstructed using the anti-$k_\text{T}$ algorithm with $R~=~0.5$, and corrected to the hadron level. Jets in our fiducial acceptance are required to have $2.0~\le~\eta~\le 4.5$ and $p_\text{T}~\ge~ 10$ GeV, and be separated from decay muons of the $Z^0/\gamma^*$ by a distance $\Delta R (\mu,\text{jet})\ge0.4$ in $\eta-\phi$ space. The cross-section ratio of $Z^0/\gamma^*(\rightarrow\mu^+\mu^-)$ + jet(s) events to $Z^0/\gamma^*\rightarrow\mu^+\mu^-$ events is measured as $0.229\pm0.011$. We also present the jet multiplicity distribution, and the $Z^0/\gamma^*$ rapidity and $p_\text{T}$ distributions for the $Z^0/\gamma^*$ + jet(s) events. Comparisons are made to NLO predictions. Our results are consistent with Standard Model predictions.