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Study of forward Z+jet production in pp collisions at $\sqrt{s}$ = 7 TeV

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Abstract

A measurement of the $Z(\rightarrow\mu^+\mu^-)$+jet production cross-section in $pp$ collisions at a centre-of-mass energy $\sqrt{s} = 7$ TeV is presented. The analysis is based on an integrated luminosity of $1.0 \text{fb}^{-1}$ recorded by the LHCb experiment. Results are shown with two jet transverse momentum thresholds, 10 and 20 GeV, for both the overall cross-section within the fiducial volume, and for six differential cross-section measurements. The fiducial volume requires that both the jet and the muons from the Z boson decay are produced in the forward direction ($2.0<\eta<4.5$). The results show good agreement with theoretical predictions at the second-order expansion in the coupling of the strong interaction.

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Jet identification efficiency as a function of the true jet $p_\text{T}$. The uncertainties shown are statistical. The zero on the vertical axis is suppressed.

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Comparison between data (black points) and simulation (red line) in the $p_\text{T}^\text{jet} / p_\text{T}^{ Z }$ distribution for selected $ Z $+1-jet events where the $ Z $ boson and the jet are emitted azimuthally opposed. The uncertainties shown are statistical.

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Ratio of the Z+jet cross-section to the inclusive cross-section, for (top) $p_\text{T}^\text{jet}> 20\text{ GeV}$ and (bottom) $p_\text{T}^\text{jet} > 10\text{ GeV}$. The bands show the LHCb measurement (with the inner band showing the statistical uncertainty and the outer band showing the total uncertainty). The points correspond to different theoretical predictions with the error bars indicating their uncertainties as described in the main text. These results are corrected for FSR from the final state muons from the $ Z $ boson decay.

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Cross-section for Z+jet production, differential in the leading jet $p_\text{T}$, for $p_\text{T}^\text{jet} > 10\text{ GeV}$. The bands show the LHCb measurement (with the inner band showing the statistical uncertainty and the outer band showing the total uncertainty). The points correspond to different theoretical predictions with the error bars indicating their uncertainties as described in the main text. Predictions are displaced horizontally for presentation. These results are not corrected for FSR from the final state muons from the $ Z $ boson decay.

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Cross-section for Z+jet production, differential in the leading jet pseudorapidity, for (left) $p_\text{T}^\text{jet}> 20\text{ GeV}$ and (right) $p_\text{T}^\text{jet} > 10\text{ GeV}$. The bands show the LHCb measurement (with the inner band showing the statistical uncertainty and the outer band showing the total uncertainty). Superimposed are predictions as described in Fig. 4.

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Cross-section for Z+jet production, differential in the $ Z $ boson rapidity, $y^ Z $, for (left) $p_\text{T}^\text{jet}> 20\text{ GeV}$ and (right) $p_\text{T}^\text{jet} > 10\text{ GeV}$. The bands show the LHCb measurement (with the inner band showing the statistical uncertainty and the outer band showing the total uncertainty). Superimposed are predictions as described in Fig. 4.

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Cross-section for Z+jet production, differential in the $ Z $ boson transverse momentum, for (left) $p_\text{T}^\text{jet}> 20\text{ GeV}$ and (right) $p_\text{T}^\text{jet} > 10\text{ GeV}$. The bands show the LHCb measurement (with the inner band showing the statistical uncertainty and the outer band showing the total uncertainty). Superimposed are predictions as described in Fig. 4.

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Cross-section for Z+jet production, differential in the difference in $\phi$ between the $ Z $ boson and the leading jet, for (left) $p_\text{T}^\text{jet}> 20\text{ GeV}$ and (right) $p_\text{T}^\text{jet} > 10\text{ GeV}$. The bands show the LHCb measurement (with the inner band showing the statistical uncertainty and the outer band showing the total uncertainty). Superimposed are predictions as described in Fig. 4.

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Cross-section for Z+jet production, differential in the difference in rapidity between the $ Z $ boson and the leading jet, for (left) $p_\text{T}^\text{jet}> 20\text{ GeV}$ and (right) $p_\text{T}^\text{jet} > 10\text{ GeV}$. The bands show the LHCb measurement (with the inner band showing the statistical uncertainty and the outer band showing the total uncertainty). Superimposed are predictions as described in Fig. 4.

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Tables and captions

The relative uncertainty arising from each source of possible systematic uncertainties considered for the Z+jet cross-section for $p_\text{T}^\text{jet}>20\text{ GeV}$. The relative uncertainties are similar for the 10 GeV threshold. The contributions from the different sources are combined in quadrature.

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Supplementary Material [file]

The supplementary material is documented in the pdf: Supp.pdf

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Created on 11 July 2020.