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

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Abstract

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

Figures and captions

$ M_{\text{corr}}$ distribution for (left) $ p_{\rm T} (\text{jet})>10\mathrm{\,GeV} $ and (right) $ p_{\rm T} (\text{jet})>20\mathrm{\,GeV} $. Data (black points) are compared to the template fit results. The uncertainties shown are statistical only.

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Efficiency of b-tagging as function of the jet transverse momentum. The uncertainties shown are statistical only.

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Z+b-jet cross-section for two $ p_{\rm T} (\text{jet})$ thresholds. The colour band shows the LHCb measurement (with the inner orange band showing the statistical uncertainty, and the outer yellow band showing the total uncertainty). The points with error bars correspond to the theoretical predictions with the inner error bars indicating their PDF uncertainties. These cross-sections are evaluated within the fiducial region $ p_{\rm T} (\mu) > 20\mathrm{\,GeV} $, $60 \mathrm{\,GeV} < M(\mu ^- \mu ^+ ) < 120 \mathrm{\,GeV} $, $2 < \eta(\text{jet}) < 4.5$, $2 < \eta(\mu) < 4.5$ and $\Delta R(\text{jet}, \mu) > 0.4$.

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Animated gif made out of all figures.

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Tables and captions

Relative systematic uncertainty considered for the Z+b-jet cross-section for $ p_{\rm T} ($jet) $>$ 20 $\mathrm{\,GeV}$ . The relative uncertainties are similar for the 10 $\mathrm{\,GeV}$ threshold. The first four contributions are from Ref. [18].

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Created on 09 December 2018.Citation count from INSPIRE on 18 December 2018.