Azimuthal correlations in Z +jets events in proton-proton collisions at s=13TeV

Abstract

The production of Z bosons associated with jets is measured in $\text{pp}$ collisions at $\sqrt{s}=13\text{Te}\text{V}$ with data recorded with the CMS experiment at the LHC corresponding to an integrated luminosity of 36.3${\text{fb}}^{-1}$. The multiplicity of jets with transverse momentum $p_{\text{T}}>30\text{Ge}\text{V}$ is measured for different regions of the Z boson's $p_{\text{T}}\left(\text{Z}\right)$, from lower than 10$\text{Ge}\text{V}$ to higher than 100$\text{Ge}\text{V}$. The azimuthal correlation $\Delta \varphi$ between the Z boson and the leading jet, as well as the correlations between the two leading jets are measured in three regions of $p_{\text{T}}\left(\text{Z}\right)$. The measurements are compared with several predictions at leading and next-to-leading orders, interfaced with parton showers. Predictions based on transverse-momentum dependent parton distributions and corresponding parton showers give a good description of the measurement in the regions where multiple parton interactions and higher jet multiplicities are not important. The effects of multiple parton interactions are shown to be important to correctly describe the measured spectra in the low $p_{\text{T}}\left(\text{Z}\right)$ regions.

Fig. 1

The exclusive jet multiplicity distribution before unfolding in three different regions of $p_{\text{T}}(\text{Z})$: $p_{\text{T}}(\text{Z})<10\text{Ge}\text{V}$ (upper), $30<p_{\text{T}}(\text{Z})<50\text{Ge}\text{V}$ (middle), $p_{\text{T}}(\text{Z})>100\text{Ge}\text{V}$ (lower) for the ${\mathrm{\mu }}^{+}$ ${\mathrm{\mu }}^{-}$ channel (left) and the ${\text{e}}^{+}{\text{e}}^{-}$ channel (right). The error bars around the data points represent the statistical uncertainties

Fig. 2

Jet multiplicity in three different regions of $p_{\text{T}}(\text{Z})$: $p_{\text{T}}(\text{Z})<10\text{Ge}\text{V}$ (upper left), $30<p_{\text{T}}(\text{Z})<50\text{Ge}\text{V}$ (upper right), $p_{\text{T}}(\text{Z})>100\text{Ge}\text{V}$ (lower). The error bars on the data points represent the statistical uncertainty of the measurement, and the hatched band shows the total statistical and systematic uncertainties added in quadrature. Predictions using MG5_aMC+Py8 ($\le 2j$ NLO) with and without MPI are shown

Fig. 3

Jet multiplicity in three different regions of $p_{\text{T}}(\text{Z})$: $p_{\text{T}}(\text{Z})<10\text{Ge}\text{V}$ (upper left), $30<p_{\text{T}}(\text{Z})<50\text{Ge}\text{V}$ (upper right), $p_{\text{T}}(\text{Z})>100\text{Ge}\text{V}$ (lower). The error bars on the data points represent the statistical uncertainty of the measurement, and the hatched band shows the total statistical and systematic uncertainties added in quadrature. Predictions from MG5_aMC+CA3 (Z +1 NLO), MG5_aMC+CA3 (Z +2 NLO) and Geneva (Z +0 NNLO) are shown. An overall normalization factor of 1.2 is applied to MG5_aMC+CA3 (Z +1 NLO) and MG5_aMC+CA3 (Z +2 NLO)

Fig. 4

Jet multiplicity in three different regions of $p_{\text{T}}(\text{Z})$: $p_{\text{T}}(\text{Z})<10\text{Ge}\text{V}$ (upper left), $30<p_{\text{T}}(\text{Z})<50\text{Ge}\text{V}$ (upper right), $p_{\text{T}}(\text{Z})>100\text{Ge}\text{V}$ (lower). The error bars on the data points represent the statistical uncertainty of the measurement, and the hatched band shows the total statistical and systematic uncertainties added in quadrature. Predictions from MG5_aMC+Py8 ($\le 4j$ LO) and MG5_aMC+CA3 (Z $\le 3j$ LO) are shown. Different normalization factors are applied, as described in the text

Fig. 5

Cross section as a function of $\Delta \varphi (\text{Z}{j}_1)$ between the Z boson and the leading jet in the three $p_{\text{T}}(\text{Z})$ bins: $p_{\text{T}}(\text{Z})<10\text{Ge}\text{V}$ (upper left), $30<p_{\text{T}}(\text{Z})<50\text{Ge}\text{V}$ (upper right), $p_{\text{T}}(\text{Z})>100\text{Ge}\text{V}$ (lower). The error bars on the data points represent the statistical uncertainty of the measurement, and the hatched band shows the total statistical and systematic uncertainties added in quadrature. Predictions using MG5_aMC+Py8 ($\le 2j$ NLO) with and without multi-parton interactions are shown

Fig. 6

Cross section as a function of $\Delta \varphi (\text{Z}{j}_1)$ between the Z boson and the leading jet in the three $p_{\text{T}}(\text{Z})$ bins: $p_{\text{T}}(\text{Z})<10\text{Ge}\text{V}$ (upper left), $30<p_{\text{T}}(\text{Z})<50\text{Ge}\text{V}$ (upper right), $p_{\text{T}}(\text{Z})>100\text{Ge}\text{V}$ (lower). The error bars on the data points represent the statistical uncertainty of the measurement, and the hatched band shows the total statistical and systematic uncertainties added in quadrature. Predictions from Geneva (Z +0 NNLO), MG5_aMC+CA3 (Z +1 NLO) and MG5_aMC+CA3 (Z +2 NLO) are shown. An overall normalization factor of 1.2 is applied to MG5_aMC+CA3 (Z +1 NLO) and MG5_aMC+CA3 (Z +2 NLO)

Fig. 7

Cross section as a function of $\Delta \varphi (\text{Z}{j}_1)$ between the Z boson and the leading jet in three $p_{\text{T}}(\text{Z})$ bins: $p_{\text{T}}(\text{Z})<10\text{Ge}\text{V}$ (upper left), $30<p_{\text{T}}(\text{Z})<50\text{Ge}\text{V}$ (upper right), $p_{\text{T}}(\text{Z})>100\text{Ge}\text{V}$ (lower). The error bars on the data points represent the statistical uncertainty of the measurement, and the hatched band shows the total statistical and systematic uncertainties added in quadrature. Predictions from MG5_aMC+Py8 ($\le 4j$ LO) and MG5_aMC+CA3 (Z $\le 3j$ LO) are shown. Different normalization factors are applied, as described in the text

Fig. 8

Cross section as a function of $\Delta \varphi (j_1{j}_2)$ between two leading jets in three $p_{\text{T}}(\text{Z})$ regions: $p_{\text{T}}(\text{Z})<10\text{Ge}\text{V}$ (upper left), $30<p_{\text{T}}(\text{Z})<50\text{Ge}\text{V}$ (upper right), $p_{\text{T}}(\text{Z})>100\text{Ge}\text{V}$ (lower). The error bars on the data points represent the statistical uncertainty of the measurement, and the hatched band shows the total statistical and systematic uncertainties added in quadrature. Predictions using MG5_aMC+Py8 ($\le 2j$ NLO) with and without multiparton interactions are shown

Fig. 9

Cross section as a function of $\Delta \varphi (j_1{j}_2)$ between two leading jets in three $p_{\text{T}}(\text{Z})$ regions: $p_{\text{T}}(\text{Z})<10\text{Ge}\text{V}$ (upper left), $30<p_{\text{T}}(\text{Z})<50\text{Ge}\text{V}$ (upper right), $p_{\text{T}}(\text{Z})>100\text{Ge}\text{V}$ (lower). The error bars on the data points represent the statistical uncertainty of the measurement, and the hatched band shows the total statistical and systematic uncertainties added in quadrature. Predictions from MG5_aMC+CA3 (Z +1 NLO), MG5_aMC+CA3 (Z +2 NLO) and Geneva (Z +0 NNLO) are shown. An overall normalization factor of 1.2 is applied to the MG5_aMC+CA3 (Z +1 NLO) and MG5_aMC+CA3 (Z +2 NLO) predictions

Fig. 10

Cross section as a function of $\Delta \varphi (j_1{j}_2)$ between two leading jets in three $p_{\text{T}}(\text{Z})$ regions: $p_{\text{T}}(\text{Z})<10\text{Ge}\text{V}$ (upper left), $30<p_{\text{T}}(\text{Z})<50\text{Ge}\text{V}$ (upper right), $p_{\text{T}}(\text{Z})>100\text{Ge}\text{V}$ (lower). The error bars on the data points represent the statistical uncertainty of the measurement, and the hatched band shows the total statistical and systematic uncertainties added in quadrature. Predictions from MG5_aMC+Py8 ($\le 4j$ LO) and MG5_aMC+CA3 (Z $\le 3j$ LO) are shown. Different normalization factors are applied, as described in the text