CMS-SMP-19-010 ; CERN-EP-2020-250 | ||
Measurements of the differential cross sections of the production of Z$+$jets and $\gamma +$jets and of Z boson emission collinear with a jet in pp collisions at $\sqrt{s} = $ 13 TeV | ||
CMS Collaboration | ||
3 February 2021 | ||
JHEP 05 (2021) 285 | ||
Abstract: Measurements of the differential cross sections of Z$+$jets and $\gamma +$jets production, and their ratio, are presented as a function of the boson transverse momentum. Measurements are also presented of the angular distribution between the Z boson and the closest jet. The analysis is based on pp collisions at a center-of-mass energy of 13 TeV corresponding to an integrated luminosity of 35.9 fb$^{-1}$ recorded by the CMS experiment at the LHC. The results, corrected for detector effects, are compared with various theoretical predictions. In general, the predictions at higher orders in perturbation theory show better agreement with the measurements. This work provides the first measurement of the ratio of the differential cross sections of Z$+$jets and $\gamma +$jets production at 13 TeV, as well as the first direct measurement of Z bosons emitted collinearly with a jet. | ||
Links: e-print arXiv:2102.02238 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; CADI line (restricted) ; |
Figures | |
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Figure 1:
A fit to the ${\sigma _{\eta \eta}}$ distribution using signal and background templates to extract a value for the purity in the photon ${p_{\mathrm {T}}}$ bin of 300-350 GeV. The signal region is to the left of the vertical dashed line (left). Purity as a function of photon ${p_{\mathrm {T}}}$, as extracted from a fit to the ${\sigma _{\eta \eta}}$ distribution in each ${p_{\mathrm {T}}}$ bin. The error bars show the total statistical and systematic uncertainty and the solid line is the fit to the data points (right). |
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Figure 1-a:
A fit to the ${\sigma _{\eta \eta}}$ distribution using signal and background templates to extract a value for the purity in the photon ${p_{\mathrm {T}}}$ bin of 300-350 GeV. The signal region is to the left of the vertical dashed line. |
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Figure 1-b:
Purity as a function of photon ${p_{\mathrm {T}}}$, as extracted from a fit to the ${\sigma _{\eta \eta}}$ distribution in each ${p_{\mathrm {T}}}$ bin. The error bars show the total statistical and systematic uncertainty and the solid line is the fit to the data points. |
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Figure 2:
Measured differential cross sections as a function of the boson ${p_{\mathrm {T}}}$ for Z$+$jets (left) and $\gamma +$jets (right) and their comparisons with several theoretical predictions. The LO MadGraph 5_aMC@NLO prediction for Z$+$jets has been normalized to the NNLO cross section (denoted by k$_{\textrm {NNLO}}$). The vertical bars in the upper panels represent the statistical uncertainty in the measurement and the hatched band in the lower and upper panels is the sum in quadrature of the statistical and systematic uncertainty components in the measurement. The lower panels show the ratios of the theoretical predictions to the unfolded data. The shaded band in the LO MadGraph 5_aMC@NLO and SHERPA + OpenLoops calculations shows the statistical uncertainty. The dark (light) shaded band on the NLO prediction from MadGraph 5_aMC@NLO and the JetPhox prediction represents the PDF (scale) uncertainties, whereas the statistical uncertainties are barely visible. |
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Figure 2-a:
Measured differential cross section as a function of the boson ${p_{\mathrm {T}}}$ for Z$+$jets and comparisons with several theoretical predictions. The LO MadGraph 5_aMC@NLO prediction for Z$+$jets has been normalized to the NNLO cross section (denoted by k$_{\textrm {NNLO}}$). The vertical bars represent the statistical uncertainty in the measurement and the hatched band is the sum in quadrature of the statistical and systematic uncertainty components in the measurement. |
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Figure 2-b:
Measured differential cross section as a function of the boson ${p_{\mathrm {T}}}$ for $\gamma +$jets |
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Figure 2-c:
Measured differential cross section as a function of the boson ${p_{\mathrm {T}}}$ for Z$+$jets and comparisons with several theoretical predictions. The panel shows the ratios of the theoretical predictions to the unfolded data. The dark (light) shaded band on the NLO prediction from MadGraph 5_aMC@NLO and the JetPhox prediction represents the PDF (scale) uncertainties, whereas the statistical uncertainties are barely visible. The hatched band is the sum in quadrature of the statistical and systematic uncertainty components in the measurement. |
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Figure 2-d:
Measured differential cross section as a function of the boson ${p_{\mathrm {T}}}$ for $\gamma +$jets and comparisons with several theoretical predictions. The panel shows the ratios of the theoretical predictions to the unfolded data. The dark (light) shaded band on the NLO prediction from MadGraph 5_aMC@NLO and the JetPhox prediction represents the PDF (scale) uncertainties, whereas the statistical uncertainties are barely visible. The hatched band is the sum in quadrature of the statistical and systematic uncertainty components in the measurement. |
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Figure 3:
Differential cross section ratio of Z$+$jets to $\gamma +$jets as a function of the vector boson (V) transverse momentum compared with the theoretical prediction from MadGraph 5_aMC@NLO and SHERPA + OpenLoops. Only vector bosons produced centrally, with $ {| y |} < $ 1.4, in association with one or more jets are considered. The lower panel shows the ratio of the theoretical prediction to the unfolded data. The vertical bars in the upper panel represent the statistical uncertainty in the measurement and the hatched band in the lower and upper panels is the sum in quadrature of the statistical and systematic uncertainty components in the measurement. The dark (light) shaded band on the NLO prediction from MadGraph 5_aMC@NLO represents the PDF (scale) uncertainties, which are treated as uncorrelated between Z$+$jets and $\gamma +$jets, whereas the statistical uncertainties are barely visible. The shaded band on the SHERPA + OpenLoops calculation is the statistical uncertainty. |
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Figure 3-a:
Differential cross section ratio of Z$+$jets to $\gamma +$jets as a function of the vector boson (V) transverse momentum compared with the theoretical prediction from MadGraph 5_aMC@NLO and SHERPA + OpenLoops. Only vector bosons produced centrally, with $ {| y |} < $ 1.4, in association with one or more jets are considered. The vertical bars represent the statistical uncertainty in the measurement. The hatched band is the sum in quadrature of the statistical and systematic uncertainty components in the measurement. |
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Figure 3-b:
Differential cross section ratio of Z$+$jets to $\gamma +$jets as a function of the vector boson (V) transverse momentum compared with the theoretical prediction from MadGraph 5_aMC@NLO and SHERPA + OpenLoops. Only vector bosons produced centrally, with $ {| y |} < $ 1.4, in association with one or more jets are considered. The panel shows the ratio of the theoretical prediction to the unfolded data. The hatched band is the sum in quadrature of the statistical and systematic uncertainty components in the measurement. The dark (light) shaded band on the NLO prediction from MadGraph 5_aMC@NLO represents the PDF (scale) uncertainties, which are treated as uncorrelated between Z$+$jets and $\gamma +$jets, whereas the statistical uncertainties are barely visible. The shaded band on the SHERPA + OpenLoops calculation is the statistical uncertainty. |
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Figure 4:
Measured differential cross section of Z$+$jets as a function of the angular separation between the Z boson and the closest jet, compared with theoretical predictions from MadGraph 5_aMC@NLO and SHERPA + OpenLoops, where the leading jet ${p_{\mathrm {T}}}$ is above 300 (left) and 500 (right) GeV. The vertical bars in the upper panel represent the statistical uncertainty in the measurement and the hatched band in the lower and upper panels is the sum in quadrature of the statistical and systematic uncertainty components in the measurement. The lower panels show the ratio of the theoretical predictions to the unfolded data. The shaded band on the LO MadGraph 5_aMC@NLO and SHERPA + OpenLoops calculations is the statistical uncertainty. The dark (light) shaded band on the NLO prediction from MadGraph 5_aMC@NLO represents the PDF (scale) uncertainties. |
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Figure 4-a:
Measured differential cross section of Z$+$jets as a function of the angular separation between the Z boson and the closest jet, compared with theoretical predictions from MadGraph 5_aMC@NLO and SHERPA + OpenLoops, where the leading jet ${p_{\mathrm {T}}}$ is above 300 GeV. The vertical bars represent the statistical uncertainty in the measurement. The hatched band is the sum in quadrature of the statistical and systematic uncertainty components in the measurement. |
png pdf |
Figure 4-b:
Measured differential cross section of Z$+$jets as a function of the angular separation between the Z boson and the closest jet, compared with theoretical predictions from MadGraph 5_aMC@NLO and SHERPA + OpenLoops, where the leading jet ${p_{\mathrm {T}}}$ is above 300 GeV. The vertical bars represent the statistical uncertainty in the measurement. The hatched band is the sum in quadrature of the statistical and systematic uncertainty components in the measurement. |
png pdf |
Figure 4-c:
Measured differential cross section of Z$+$jets as a function of the angular separation between the Z boson and the closest jet, compared with theoretical predictions from MadGraph 5_aMC@NLO and SHERPA + OpenLoops, where the leading jet ${p_{\mathrm {T}}}$ is above 300 GeV. The panel shows the ratio of the theoretical predictions to the unfolded data. The hatched band is the sum in quadrature of the statistical and systematic uncertainty components in the measurement. The shaded band on the LO MadGraph 5_aMC@NLO and SHERPA + OpenLoops calculations is the statistical uncertainty. The dark (light) shaded band on the NLO prediction from MadGraph 5_aMC@NLO represents the PDF (scale) uncertainties. |
png pdf |
Figure 4-d:
Measured differential cross section of Z$+$jets as a function of the angular separation between the Z boson and the closest jet, compared with theoretical predictions from MadGraph 5_aMC@NLO and SHERPA + OpenLoops, where the leading jet ${p_{\mathrm {T}}}$ is above 300 GeV. The panel shows the ratio of the theoretical predictions to the unfolded data. The hatched band is the sum in quadrature of the statistical and systematic uncertainty components in the measurement. The shaded band on the LO MadGraph 5_aMC@NLO and SHERPA + OpenLoops calculations is the statistical uncertainty. The dark (light) shaded band on the NLO prediction from MadGraph 5_aMC@NLO represents the PDF (scale) uncertainties. |
Tables | |
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Table 1:
The contributions to the uncertainty in the differential cross section measurements for the Z$+$jets and $\gamma +$jets processes, the Z/$\gamma$ ratio, and the ${{{\Delta R}}_{\mathrm{Z},\text {j}}}$ region. The uncertainties are expressed in percent, and a range represents the minimum and maximum effect observed. |
Summary |
This paper presents measurements of standard model processes that probe regions of phase space characterized by the production of Z$+$jets and $\gamma +$jets at large boson transverse momentum (${p_{\mathrm{T}}}$), and of a Z boson in association with at least one very high ${p_{\mathrm{T}}}$ jet. The measurements utilize data recorded with the CMS detector in pp collisions at $\sqrt{s}$ = 13 TeV at the LHC that correspond to an integrated luminosity of 35.9 fb$^{-1}$. Comparisons are made between the unfolded data and several theory predictions. The Z$+$jets and $\gamma +$jets cross sections as a function of boson ${p_{\mathrm{T}}}$ are presented for ${p_{\mathrm{T}}}$ above 200 GeV and compared with predictions from (i) the leading-order (LO) and next-to-leading-order (NLO) calculations from MadGraph5+MCatNLO, and (ii) the NLO quantum chromodynamics and electroweak (QCD+EW) calculation from SHERPA + OpenLoops . In addition, the $\gamma +$jets measurement is compared with NLO JetPhox predictions. The data are consistent with theory for both the $\gamma$ and Z boson final states, although in some regions of phase space a few tens of percent deviations are observed. In general, the perturbative NLO corrections exhibit a better agreement with the measurements. This is the first measurement at 13 TeV of the ratio of cross sections for Z$+$jets to $\gamma +$jets as a function of boson ${p_{\mathrm{T}}}$. This ratio is compared with the NLO calculation from MadGraph5+MCatNLO and the NLO QCD+EW prediction from SHERPA + OpenLoops ; and it probes the region up to 1.5 TeV in boson ${p_{\mathrm{T}}}$. The data are generally in agreement with theory within the uncertainties over the full range of boson ${p_{\mathrm{T}}}$. This ratio provides an important theoretical input for the estimation, based on the $\gamma +$jets process, of the ${\mathrm{Z}\to\mathrm{\nu\bar{nu}}} $ background relevant in searches for new physics. The measurement of the emission of a Z boson collinear to a jet represents the first explicit study of this topology at the LHC. It is accessed through the production of a Z boson in association with at least one high-${p_{\mathrm{T}}}$ jet ($ > $300 or $ > $500 GeV), and the differential cross section is measured as a function of the angular separation between the Z boson and the closest jet (${{{\Delta R} }_{\mathrm{Z},\text{j}}} $). The unfolded data are compared with the LO and NLO calculations from MadGraph5+MCatNLO, and the NLO QCD+EW prediction from SHERPA + OpenLoops . The NLO {MadGraph} shows agreement over most of the measured distribution, but underpredicts it for the ${{{\Delta R} }_{\mathrm{Z},\text{j}}} $ region below 0.8, which is dominated by events with the emission of a Z boson in close proximity to a jet. The prediction from SHERPA is also generally consistent with the measurement. The measurements presented in this paper will become increasingly important in current and future runs of the LHC, where the higher $\sqrt{s}$ and larger integrated luminosity will push the LHC program into new territory, necessitating an understanding of standard model processes in regions of previously unexplored phase space. |
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