# Measurement of forward $W$ and $Z$ boson production in association with jets in proton-proton collisions at $\sqrt{s}=8$ TeV

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## Abstract

The production of $W$ and $Z$ bosons in association with jets is studied in the forward region of proton-proton collisions collected at a centre-of-mass energy of 8 TeV by the LHCb experiment, corresponding to an integrated luminosity of 1.98 $\pm$ 0.02 fb$^{-1}$. The $W$ boson is identified using its decay to a muon and a neutrino, while the $Z$ boson is identified through its decay to a muon pair. Total cross-sections are measured and combined into charge ratios, asymmetries, and ratios of $W+$jet and $Z$+jet production cross-sections. Differential measurements are also performed as a function of both boson and jet kinematic variables. All results are in agreement with Standard Model predictions.

## Figures and captions

 The contributions to the selected (left) $W ^+ {j}$ and (right) $W ^- {j}$ samples are shown, where the QCD background is obtained by a fit to the $p_{\textrm{T}}^{\mu}$ / $p_{\textrm{T}}^{\mu\textrm{-jet} }$ spectrum and the electroweak background is determined as described in the text. The contributions shown are the sum of the individual contributions in bins of $\eta^{\textrm{jet}}$ , where the charge asymmetry typical of $W {j}$ production in $pp$ collisions is evident. Fig1l.pdf [15 KiB] HiDef png [160 KiB] Thumbnail [149 KiB] *.C file Fig1r.pdf [15 KiB] HiDef png [155 KiB] Thumbnail [146 KiB] *.C file Summary of the measurements performed in the fiducial region, as defined in Sec. 1. The measurements are shown as bands, while the theoretical predictions are presented as points. For the experimental measurements, the inner band represents the statistical uncertainty, while the outer band represents the total uncertainty. For the theory points, the inner error bar represents the scale uncertainty, while the outer bar represents the total uncertainty. The cross-sections and ratios are shown normalised to the measurement, while the asymmetry is presented separately. Fig2.pdf [15 KiB] HiDef png [151 KiB] Thumbnail [130 KiB] *.C file $W {j}$ bin-averaged differential cross-sections as a function of $\eta^{\mu}$ (left) and $\eta^{\textrm{jet}}$ (right). The measurements are shown as bands representing the statistical and total uncertainties, while the theoretical predictions are shown as points (displaced horizontally for presentation) representing the same bin-averaged cross-sections as the data. The inner error bar represents the scale uncertainty, and the outer error bar represents the total uncertainty. The ratio of the predicted to measured cross-sections is shown below the distribution. The $W ^+ {j}$ and $W ^- {j}$ cross-sections are seen to overlap in the final bin in $\eta^{\mu}$ . Fig3l.pdf [18 KiB] HiDef png [218 KiB] Thumbnail [198 KiB] *.C file Fig3r.pdf [18 KiB] HiDef png [229 KiB] Thumbnail [215 KiB] *.C file $W {j}$ bin-averaged differential cross-sections as a function of $p_{\textrm{T}}^{\textrm{jet}}$ . The experimental and theoretical components are shown as in Fig. 3. The ratio of the predicted to measured cross-sections is shown below the distribution. Fig4.pdf [19 KiB] HiDef png [243 KiB] Thumbnail [212 KiB] *.C file The measured bin-averaged differential $Z {j}$ production cross-section is shown as a function of (left) $\eta^{\textrm{jet}}$ and (right) $p_{\textrm{T}}^{\textrm{jet}}$ . The experimental measurements are shown as bands, while the theoretical predictions are shown as points, horizontally displaced for presentation. The ratio of the predicted to measured cross-sections is shown below the distribution. Fig5l.pdf [15 KiB] HiDef png [157 KiB] Thumbnail [152 KiB] *.C file Fig5r.pdf [16 KiB] HiDef png [175 KiB] Thumbnail [163 KiB] *.C file The measured bin-averaged differential $Z {j}$ production cross-section is shown as a function of (left) $y^{ Z }$ and (right) azimuthal separation between the $Z$ boson and the jet. The experimental measurements are shown as bands, while the theoretical predictions are shown as points, horizontally displaced for presentation. The ratio of the predicted to measured cross-sections is shown below the distribution. Fig6l.pdf [15 KiB] HiDef png [153 KiB] Thumbnail [149 KiB] *.C file Fig6r.pdf [16 KiB] HiDef png [157 KiB] Thumbnail [147 KiB] *.C file Ratio (left) and asymmetry (right) of $W ^+ {j}$ to $W ^- {j}$ production as a function of the lepton pseudorapidity. The experimental measurements are shown as bands, while the theoretical predictions are shown as points, horizontally displaced for presentation. The ratio of the predictions to the experimentally measured values is shown below the distribution for the charge ratio, while their difference is shown for the charge asymmetry. Fig7l.pdf [15 KiB] HiDef png [131 KiB] Thumbnail [126 KiB] *.C file Fig7r.pdf [15 KiB] HiDef png [156 KiB] Thumbnail [155 KiB] *.C file Ratio (left) and asymmetry (right) of $W ^+ {j}$ to $W ^- {j}$ production as a function of the lepton pseudorapidity compared to NLO calculations performed with the Fewz generator and three different PDF sets. The experimental measurements are shown as bands, while the theoretical predictions are shown as points, horizontally displaced for presentation. The same comparisons are shown below the distribution as described in Fig. 7. Fig8l.pdf [15 KiB] HiDef png [136 KiB] Thumbnail [127 KiB] *.C file Fig8r.pdf [16 KiB] HiDef png [161 KiB] Thumbnail [155 KiB] *.C file Animated gif made out of all figures. PAPER-2016-011.gif Thumbnail

## Tables and captions

 Summary of the different contributions to the total uncertainty on $\sigma_{ W ^+ {j} }$ , $\sigma_{ W ^- {j} }$ , $\sigma_{ Z {j} }$ and their ratios given as a percentage of the measured observable. Table_1.pdf [47 KiB] HiDef png [110 KiB] Thumbnail [55 KiB] tex code

## Supplementary Material [file]

 Supplementary material full pdf supple[..].pdf [118 KiB]

Created on 11 January 2020.