Measurement of the production cross section for $Z/\gamma *$ in association with jets in $pp$ collisions at $\sqrt{s}=7\mathrm{TeV}$ with the ATLAS detector

Results are presented on the production of jets of particles in association with a $Z/{\gamma }^{*}$ boson, in proton-proton collisions at $\sqrt{s}=7\mathrm{TeV}$ with the ATLAS detector. The analysis includes the full 2010 data set, collected with a low rate of multiple proton-proton collisions in the accelerator, corresponding to an integrated luminosity of $36{\mathrm{pb}}^{-1}$. Inclusive jet cross sections in $Z/{\gamma }^{*}$ events, with $Z/{\gamma }^{*}$ decaying into electron or muon pairs, are measured for jets with transverse momentum $p_T>30\mathrm{GeV}$ and jet rapidity $|y|<4.4$. The measurements are compared to next-to-leading-order perturbative QCD calculations, and to predictions from different Monte Carlo generators implementing leading-order matrix elements supplemented by parton showers.

Figure 1

Uncorrected dilepton invariant mass in (top) $Z/{\gamma }^{*}\to e^{+}{e}^{-}$ and (bottom) $Z/{\gamma }^{*}\to {\mu }^{+}{\mu }^{-}$ events with at least one jet in the final state, shown in a wider dilepton mass region than the one selected (left), and uncorrected inclusive jet multiplicity (right), for jets with $p_T>30\mathrm{GeV}$ and $|y|<4.4$ (black dots), and in the mass range $66\mathrm{GeV}<m_{{\ell }^{+}{\ell }^{-}}<116\mathrm{GeV}$ ($\ell =e$, $\mu$). Only statistical uncertainties are shown. The data are compared to predictions for signal (ALPGEN and Sherpa, both normalized to the FEWZ value for the total cross section) and background processes (filled histograms).

Figure 2

Relative systematic uncertainties from different sources in the (top) $Z/{\gamma }^{*}(\to e^{+}{e}^{-})+\mathrm{\text{jets}}$ and (bottom) $Z/{\gamma }^{*}(\to {\mu }^{+}{\mu }^{-})+\mathrm{\text{jets}}$ analyses for the measured cross section as a function of inclusive jet multiplicity, and the inclusive differential cross sections as a function of $p_T$, for events with at least one jet with $p_T>30\mathrm{GeV}$ and $|y|<4.4$ in the final state (see Sec. 10). The total systematic uncertainty is obtained by summing all contributions in quadrature.

Figure 3

Measured cross section ${\sigma }_{N_{\mathrm{jet}}}$ (black dots) for (left) $Z/{\gamma }^{*}(\to e^{+}{e}^{-})+\mathrm{\text{jets}}$ and (right) $Z/{\gamma }^{*}(\to {\mu }^{+}{\mu }^{-})+\mathrm{\text{jets}}$ production as a function of the inclusive jet multiplicity, for events with at least one jet with $p_T>30\mathrm{GeV}$ and $|y|<4.4$ in the final state. In this and subsequent Figs. 4 and 14 the error bars indicate the statistical uncertainty and the dashed areas the statistical and systematic uncertainties added in quadrature. The measurements are compared to NLO pQCD predictions from BlackHat, as well as the predictions from ALPGEN and Sherpa (both normalized to the FEWZ value for the total cross section), and PYTHIA (normalized to the data as discussed in Sec. 12).

Figure 4

Measured ratio of cross sections (${\sigma }_{N_{\mathrm{jet}}}/{\sigma }_{N_{\mathrm{jet}}-1}$) (black dots) for (left) $Z/{\gamma }^{*}(\to e^{+}{e}^{-})+\mathrm{\text{jets}}$ and (right) $Z/{\gamma }^{*}(\to {\mu }^{+}{\mu }^{-})+\mathrm{\text{jets}}$ production as a function of the inclusive jet multiplicity, for events with at least one jet with $p_T>30\mathrm{GeV}$ and $|y|<4.4$ in the final state.

Figure 5

Measured normalized inclusive jet cross section $(1/{\sigma }_{Z/{\gamma }^{*}\to {\ell }^{+}{\ell }^{-}})d\sigma /d{p}_T$ (black dots) in (left) $Z/{\gamma }^{*}(\to e^{+}{e}^{-})+\mathrm{\text{jets}}$ and (right) $Z/{\gamma }^{*}(\to {\mu }^{+}{\mu }^{-})+\mathrm{\text{jets}}$ production as a function of $p_T$, in events with at least one jet with $p_T>30\mathrm{GeV}$ and $|y|<4.4$ in the final state, and normalized by ${\sigma }_{Z/{\gamma }^{*}\to e^{+}{e}^{-}}$ and ${\sigma }_{Z/{\gamma }^{*}\to {\mu }^{+}{\mu }^{-}}$ Drell-Yan cross sections, respectively.

Figure 6

Measured normalized jet cross section $(1/{\sigma }_{Z/{\gamma }^{*}\to {\ell }^{+}{\ell }^{-}})d\sigma /d{p}_T$ (black dots) in (left) $Z/{\gamma }^{*}(\to e^{+}{e}^{-})+\mathrm{\text{jets}}$ and (right) $Z/{\gamma }^{*}(\to {\mu }^{+}{\mu }^{-})+\mathrm{\text{jets}}$ production as a function of the leading jet $p_T$, in events with at least one jet with $p_T>30\mathrm{GeV}$ and $|y|<4.4$ in the final state, and normalized by ${\sigma }_{Z/{\gamma }^{*}\to e^{+}{e}^{-}}$ and ${\sigma }_{Z/{\gamma }^{*}\to {\mu }^{+}{\mu }^{-}}$ Drell-Yan cross sections, respectively.

Figure 7

Measured normalized jet cross section $(1/{\sigma }_{Z/{\gamma }^{*}\to {\ell }^{+}{\ell }^{-}})d\sigma /d{p}_T$ (black dots) in (left) $Z/{\gamma }^{*}(\to e^{+}{e}^{-})+\mathrm{\text{jets}}$ and (right) $Z/{\gamma }^{*}(\to {\mu }^{+}{\mu }^{-})+\mathrm{\text{jets}}$ production as a function of the second-leading jet $p_T$, in events with at least two jets with $p_T>30\mathrm{GeV}$ and $|y|<4.4$ in the final state, and normalized by ${\sigma }_{Z/{\gamma }^{*}\to e^{+}{e}^{-}}$ and ${\sigma }_{Z/{\gamma }^{*}\to {\mu }^{+}{\mu }^{-}}$ Drell-Yan cross sections, respectively.

Figure 8

Measured normalized inclusive jet cross section $(1/{\sigma }_{Z/{\gamma }^{*}\to {\ell }^{+}{\ell }^{-}})d\sigma /d|y|$ (black dots) in (left) $Z/{\gamma }^{*}(\to e^{+}{e}^{-})+\mathrm{\text{jets}}$ and (right) $Z/{\gamma }^{*}(\to {\mu }^{+}{\mu }^{-})+\mathrm{\text{jets}}$ production as a function of $|y|$, in events with at least one jet with $p_T>30\mathrm{GeV}$ and $|y|<4.4$ in the final state, and normalized by ${\sigma }_{Z/{\gamma }^{*}\to e^{+}{e}^{-}}$ and ${\sigma }_{Z/{\gamma }^{*}\to {\mu }^{+}{\mu }^{-}}$ Drell-Yan cross sections, respectively.

Figure 9

Measured normalized jet cross section $(1/{\sigma }_{Z/{\gamma }^{*}\to {\ell }^{+}{\ell }^{-}})d\sigma /d|y|$ (black dots) in (left) $Z/{\gamma }^{*}(\to e^{+}{e}^{-})+\mathrm{\text{jets}}$ and (right) $Z/{\gamma }^{*}(\to {\mu }^{+}{\mu }^{-})+\mathrm{\text{jets}}$ production as a function of the leading jet $|y|$, in events with at least one jet with $p_T>30\mathrm{GeV}$ and $|y|<4.4$ in the final state, and normalized by ${\sigma }_{Z/{\gamma }^{*}\to e^{+}{e}^{-}}$ and ${\sigma }_{Z/{\gamma }^{*}\to {\mu }^{+}{\mu }^{-}}$ Drell-Yan cross sections, respectively.

Figure 10

Measured normalized jet cross section $(1/{\sigma }_{Z/{\gamma }^{*}\to {\ell }^{+}{\ell }^{-}})d\sigma /d|y|$ (black dots) in (left) $Z/{\gamma }^{*}(\to e^{+}{e}^{-})+\mathrm{\text{jets}}$ and (right) $Z/{\gamma }^{*}(\to {\mu }^{+}{\mu }^{-})+\mathrm{\text{jets}}$ production as a function of the second-leading jet $|y|$, in events with at least two jets with $p_T>30\mathrm{GeV}$ and $|y|<4.4$ in the final state, and normalized by ${\sigma }_{Z/{\gamma }^{*}\to e^{+}{e}^{-}}$ and ${\sigma }_{Z/{\gamma }^{*}\to {\mu }^{+}{\mu }^{-}}$ Drell-Yan cross sections, respectively.

Figure 11

Measured normalized dijet cross section $(1/{\sigma }_{Z/{\gamma }^{*}\to {\ell }^{+}{\ell }^{-}})d\sigma /d{m}^{jj}$ (black dots) in (left) $Z/{\gamma }^{*}(\to e^{+}{e}^{-})+\mathrm{\text{jets}}$ and (right) $Z/{\gamma }^{*}(\to {\mu }^{+}{\mu }^{-})+\mathrm{\text{jets}}$ production as a function of the invariant mas of the two leading jets $m^{jj}$, in events with at least two jets with $p_T>30\mathrm{GeV}$ and $|y|<4.4$ in the final state, and normalized by ${\sigma }_{Z/{\gamma }^{*}\to e^{+}{e}^{-}}$ and ${\sigma }_{Z/{\gamma }^{*}\to {\mu }^{+}{\mu }^{-}}$ Drell-Yan cross sections, respectively.

Figure 12

Measured normalized dijet cross section $(1/{\sigma }_{Z/{\gamma }^{*}\to {\ell }^{+}{\ell }^{-}})d\sigma /d|\Delta y^{jj}|$ (black dots) in (left) $Z/{\gamma }^{*}(\to e^{+}{e}^{-})+\mathrm{\text{jets}}$ and (right) $Z/{\gamma }^{*}(\to {\mu }^{+}{\mu }^{-})+\mathrm{\text{jets}}$ production as a function of the rapidity separation of the two leading jets $|\Delta y^{jj}|$, in events with at least two jets with $p_T>30\mathrm{GeV}$ and $|y|<4.4$ in the final state, and normalized by ${\sigma }_{Z/{\gamma }^{*}\to e^{+}{e}^{-}}$ and ${\sigma }_{Z/{\gamma }^{*}\to {\mu }^{+}{\mu }^{-}}$ Drell-Yan cross sections, respectively.

Figure 13

Measured normalized dijet cross section $(1/{\sigma }_{Z/{\gamma }^{*}\to {\ell }^{+}{\ell }^{-}})d\sigma /d|\Delta {\varphi }^{jj}|$ (black dots) in (left) $Z/{\gamma }^{*}(\to e^{+}{e}^{-})+\mathrm{\text{jets}}$ and (right) $Z/{\gamma }^{*}(\to {\mu }^{+}{\mu }^{-})+\mathrm{\text{jets}}$ production as a function of the azimuthal separation of the two leading jets $|\Delta {\varphi }^{jj}|$, in events with at least two jets with $p_T>30\mathrm{GeV}$ and $|y|<4.4$ in the final state, and normalized by ${\sigma }_{Z/{\gamma }^{*}\to e^{+}{e}^{-}}$ and ${\sigma }_{Z/{\gamma }^{*}\to {\mu }^{+}{\mu }^{-}}$ Drell-Yan cross sections, respectively.

Figure 14

Measured normalized dijet cross section $(1/{\sigma }_{Z/{\gamma }^{*}\to {\ell }^{+}{\ell }^{-}})d\sigma /d\Delta R^{jj}$ (black dots) in (left) $Z/{\gamma }^{*}(\to e^{+}{e}^{-})+\mathrm{\text{jets}}$ and (right) $Z/{\gamma }^{*}(\to {\mu }^{+}{\mu }^{-})+\mathrm{\text{jets}}$ production as a function of the angular separation ($y-\varphi$ space) of the two leading jets $\Delta R^{jj}$, in events with at least two jets with $p_T>30\mathrm{GeV}$ and $|y|<4.4$ in the final state, and normalized by ${\sigma }_{Z/{\gamma }^{*}\to e^{+}{e}^{-}}$ and ${\sigma }_{Z/{\gamma }^{*}\to {\mu }^{+}{\mu }^{-}}$ Drell-Yan cross sections, respectively.

Figure 15

Measured cross section ${\sigma }_{N_{\mathrm{jet}}}$ (black dots) in $Z/{\gamma }^{*}(\to {\ell }^{+}{\ell }^{-})+\mathrm{\text{jets}}$ production as a function of the inclusive jet multiplicity, for events with at least one jet with $p_T>30\mathrm{GeV}$ and $|y|<4.4$ in the final state. In this and subsequent Figs. 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26 the error bands indicate the total uncertainty from the combination of electron and muon results. The measurements are compared to NLO pQCD predictions from BlackHat, as well as the predictions from ALPGEN and Sherpa (both normalized to the FEWZ value for the total cross section).

Figure 16

Measured ratio of cross sections (${\sigma }_{N_{\mathrm{jet}}}/{\sigma }_{N_{\mathrm{jet}}-1}$) (black dots) in $Z/{\gamma }^{*}(\to {\ell }^{+}{\ell }^{-})+\mathrm{\text{jets}}$ production as a function of the inclusive jet multiplicity, for events with at least one jet with $p_T>30\mathrm{GeV}$ and $|y|<4.4$ in the final state.

Figure 17

Measured inclusive jet cross section $d\sigma /d{p}_T$ (black dots) in $Z/{\gamma }^{*}(\to {\ell }^{+}{\ell }^{-})+\mathrm{\text{jets}}$ production as a function of $p_T$, in events with at least one jet with $p_T>30\mathrm{GeV}$ and $|y|<4.4$ in the final state.

Figure 18

Measured jet cross section $d\sigma /d{p}_T$ (black dots) in $Z/{\gamma }^{*}(\to {\ell }^{+}{\ell }^{-})+\mathrm{\text{jets}}$ production as a function of the leading jet $p_T$, in events with at least one jet with $p_T>30\mathrm{GeV}$ and $|y|<4.4$ in the final state.

Figure 19

Measured jet cross section $d\sigma /d{p}_T$ (black dots) in $Z/{\gamma }^{*}(\to {\ell }^{+}{\ell }^{-})+\mathrm{\text{jets}}$ production as a function of the second-leading jet $p_T$, in events with at least two jets with $p_T>30\mathrm{GeV}$ and $|y|<4.4$ in the final state.

Figure 20

Measured inclusive jet cross section $d\sigma /d|y|$ (black dots) in $Z/{\gamma }^{*}(\to {\ell }^{+}{\ell }^{-})+\mathrm{\text{jets}}$ production as a function of $|y|$, in events with at least one jet with $p_T>30\mathrm{GeV}$ and $|y|<4.4$ in the final state.

Figure 21

Measured jet cross section $d\sigma /d|y|$ (black dots) in $Z/{\gamma }^{*}(\to {\ell }^{+}{\ell }^{-})+\mathrm{\text{jets}}$ production as a function of the leading jet $|y|$, in events with at least one jet with $p_T>30\mathrm{GeV}$ and $|y|<4.4$ in the final state.

Figure 22

Measured jet cross section $d\sigma /d|y|$ (black dots) in $Z/{\gamma }^{*}(\to {\ell }^{+}{\ell }^{-})+\mathrm{\text{jets}}$ production as a function of the second-leading jet $|y|$, in events with at least two jets with $p_T>30\mathrm{GeV}$ and $|y|<4.4$ in the final state.

Figure 23

Measured dijet cross section $d\sigma /d{m}^{jj}$ (black dots) in $Z/{\gamma }^{*}(\to {\ell }^{+}{\ell }^{-})+\mathrm{\text{jets}}$ production as a function of the invariant mass of the two leading jets $m^{jj}$, in events with at least two jets with $p_T>30\mathrm{GeV}$ and $|y|<4.4$ in the final state.

Figure 24

Measured dijet cross section $d\sigma /d|\Delta y^{jj}|$ (black dots) in $Z/{\gamma }^{*}(\to {\ell }^{+}{\ell }^{-})+\mathrm{\text{jets}}$ production as a function of the rapidity separation of the two leading jets $|\Delta y^{jj}|$, in events with at least two jets with $p_T>30\mathrm{GeV}$ and $|y|<4.4$ in the final state.

Figure 25

Measured dijet cross section $d\sigma /d|\Delta {\varphi }^{jj}|$ (black dots) in $Z/{\gamma }^{*}(\to {\ell }^{+}{\ell }^{-})+\mathrm{\text{jets}}$ production as a function of the azimuthal separation of the two leading jets $|\Delta {\varphi }^{jj}|$, in events with at least two jets with $p_T>30\mathrm{GeV}$ and $|y|<4.4$ in the final state.

Figure 26

Measured dijet cross section $d\sigma /d\Delta R^{jj}$ (black dots) in $Z/{\gamma }^{*}(\to {\ell }^{+}{\ell }^{-})+\mathrm{\text{jets}}$ production as a function of the angular separation ($y-\varphi$ space) of the two leading jets $\Delta R^{jj}$, in events with at least two jets with $p_T>30\mathrm{GeV}$ and $|y|<4.4$ in the final state.