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| CMS-PAS-SMP-19-010 | ||
| Measurement of the differential Z+jets and $\gamma$+jets cross sections, their ratio, and collinear Z boson emission in pp collisions at $\sqrt{s}=$ 13 TeV | ||
| CMS Collaboration | ||
| May 2020 | ||
| Abstract: Measurements of the differential cross sections of Z+jets, $\gamma$+jets, and their ratio, are presented as a function of the boson transverse momentum. Measurements are also presented of the Z boson angular distribution in events where the Z boson is emitted collinear to a jet with very high transverse momentum. The analysis is based on a data sample of proton-proton 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 data are compared to different theoretical predictions after correcting for detector effects and show varying levels of agreement. In general, the predictions at higher orders in perturbation theory show better agreement with the data. | ||
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These preliminary results are superseded in this paper, JHEP 05 (2021) 285. The superseded preliminary plots can be found here. |
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| 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 (left). The purity value 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 (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 (left). The purity value 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 (right). |
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Figure 1-b:
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 (left). The purity value 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 (right). |
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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 error bars in the upper panels represent the statistical uncertainty on the measurement and the hatched band in the lower and upper panels is the sum in quadrature of the statistical and systematic uncertainty on the measurement. The lower panels show the ratio of the theory predictions to the unfolded data. The shaded error band on the LO MadGraph 5_aMC@NLO calculation is the statistical uncertainty. The dark (light) shaded error band on the NLO prediction from MadGraph 5_aMC@NLO and the JetPhox prediction represents the PDF (scale) uncertainties. |
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Figure 2-a:
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 error bars in the upper panels represent the statistical uncertainty on the measurement and the hatched band in the lower and upper panels is the sum in quadrature of the statistical and systematic uncertainty on the measurement. The lower panels show the ratio of the theory predictions to the unfolded data. The shaded error band on the LO MadGraph 5_aMC@NLO calculation is the statistical uncertainty. The dark (light) shaded error band on the NLO prediction from MadGraph 5_aMC@NLO and the JetPhox prediction represents the PDF (scale) uncertainties. |
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Figure 2-b:
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 error bars in the upper panels represent the statistical uncertainty on the measurement and the hatched band in the lower and upper panels is the sum in quadrature of the statistical and systematic uncertainty on the measurement. The lower panels show the ratio of the theory predictions to the unfolded data. The shaded error band on the LO MadGraph 5_aMC@NLO calculation is the statistical uncertainty. The dark (light) shaded error band on the NLO prediction from MadGraph 5_aMC@NLO and the JetPhox prediction represents the PDF (scale) uncertainties. |
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Figure 2-c:
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 error bars in the upper panels represent the statistical uncertainty on the measurement and the hatched band in the lower and upper panels is the sum in quadrature of the statistical and systematic uncertainty on the measurement. The lower panels show the ratio of the theory predictions to the unfolded data. The shaded error band on the LO MadGraph 5_aMC@NLO calculation is the statistical uncertainty. The dark (light) shaded error band on the NLO prediction from MadGraph 5_aMC@NLO and the JetPhox prediction represents the PDF (scale) uncertainties. |
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Figure 2-d:
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 error bars in the upper panels represent the statistical uncertainty on the measurement and the hatched band in the lower and upper panels is the sum in quadrature of the statistical and systematic uncertainty on the measurement. The lower panels show the ratio of the theory predictions to the unfolded data. The shaded error band on the LO MadGraph 5_aMC@NLO calculation is the statistical uncertainty. The dark (light) shaded error band on the NLO prediction from MadGraph 5_aMC@NLO and the JetPhox prediction represents the PDF (scale) uncertainties. |
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Figure 3:
Differential cross section ratio of Z+jets over $\gamma$+jets as a function of the vector boson transverse momentum compared to the theoretical prediction from MadGraph 5_aMC@NLO. Only vector bosons produced centrally, with $|y| < $ 1.4, in association with one or more jets, are considered. The error bars in the upper panel represent the statistical uncertainty on the measurement and the hatched band in the lower and upper panels is the sum in quadrature of the statistical and systematic uncertainty on the measurement. The lower panels show the ratio of the theory prediction to the unfolded data. The dark (light) shaded error 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. |
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Figure 3-a:
Differential cross section ratio of Z+jets over $\gamma$+jets as a function of the vector boson transverse momentum compared to the theoretical prediction from MadGraph 5_aMC@NLO. Only vector bosons produced centrally, with $|y| < $ 1.4, in association with one or more jets, are considered. The error bars in the upper panel represent the statistical uncertainty on the measurement and the hatched band in the lower and upper panels is the sum in quadrature of the statistical and systematic uncertainty on the measurement. The lower panels show the ratio of the theory prediction to the unfolded data. The dark (light) shaded error 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. |
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Figure 3-b:
Differential cross section ratio of Z+jets over $\gamma$+jets as a function of the vector boson transverse momentum compared to the theoretical prediction from MadGraph 5_aMC@NLO. Only vector bosons produced centrally, with $|y| < $ 1.4, in association with one or more jets, are considered. The error bars in the upper panel represent the statistical uncertainty on the measurement and the hatched band in the lower and upper panels is the sum in quadrature of the statistical and systematic uncertainty on the measurement. The lower panels show the ratio of the theory prediction to the unfolded data. The dark (light) shaded error 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. |
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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 and the comparison with theory predictions from MadGraph 5_aMC@NLO where the leading jet ${p_{\mathrm {T}}}$ is $ > $ 300 GeV (left) and 500 GeV (right). The error bars in the upper panel represent the statistical uncertainty on the measurement and the hatched band in the lower and upper panels is the sum in quadrature of the statistical and systematic uncertainty on the measurement. The lower panel shows the ratio of the theory predictions to the unfolded data. The dark (light) shaded error band on the NLO prediction from MadGraph 5_aMC@NLO represents the PDF (scale) uncertainties. |
png pdf |
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 and the comparison with theory predictions from MadGraph 5_aMC@NLO where the leading jet ${p_{\mathrm {T}}}$ is $ > $ 300 GeV (left) and 500 GeV (right). The error bars in the upper panel represent the statistical uncertainty on the measurement and the hatched band in the lower and upper panels is the sum in quadrature of the statistical and systematic uncertainty on the measurement. The lower panel shows the ratio of the theory predictions to the unfolded data. The dark (light) shaded error band on the NLO prediction from MadGraph 5_aMC@NLO represents the PDF (scale) uncertainties. |
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 and the comparison with theory predictions from MadGraph 5_aMC@NLO where the leading jet ${p_{\mathrm {T}}}$ is $ > $ 300 GeV (left) and 500 GeV (right). The error bars in the upper panel represent the statistical uncertainty on the measurement and the hatched band in the lower and upper panels is the sum in quadrature of the statistical and systematic uncertainty on the measurement. The lower panel shows the ratio of the theory predictions to the unfolded data. The dark (light) shaded error band on the NLO prediction from MadGraph 5_aMC@NLO represents the PDF (scale) uncertainties. |
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 and the comparison with theory predictions from MadGraph 5_aMC@NLO where the leading jet ${p_{\mathrm {T}}}$ is $ > $ 300 GeV (left) and 500 GeV (right). The error bars in the upper panel represent the statistical uncertainty on the measurement and the hatched band in the lower and upper panels is the sum in quadrature of the statistical and systematic uncertainty on the measurement. The lower panel shows the ratio of the theory predictions to the unfolded data. The dark (light) shaded error 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 and the comparison with theory predictions from MadGraph 5_aMC@NLO where the leading jet ${p_{\mathrm {T}}}$ is $ > $ 300 GeV (left) and 500 GeV (right). The error bars in the upper panel represent the statistical uncertainty on the measurement and the hatched band in the lower and upper panels is the sum in quadrature of the statistical and systematic uncertainty on the measurement. The lower panel shows the ratio of the theory predictions to the unfolded data. The dark (light) shaded error 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 on the differential cross section measurements for the Z+jets, $\gamma$+jets, the Z$/\gamma $ ratio and collinear Z boson regions. The uncertainties are expressed in percent and a range represents the mininimum and maximum effect observed. |
| Summary |
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The results reported in this note extend the measurements of standard model processes to probe extreme regions of phase space characterized by the production of Z+jets and ${\gamma}$+jets at large boson ${p_{\mathrm{T}}}$ and the boosted production of a ${\text{Z}} $ boson in association with at least one very high ${p_{\mathrm{T}}}$ jet. The measurements utilize data recorded by the CMS detector from pp collisions at $\sqrt{s} =$ 13 TeV at the LHC, corresponding to an integrated luminosity of 35.9 fb$^{-1}$. Comparisons are made between the unfolded data distributions and a variety of predictions from theoretical calculations. The differential measurement of the Z+jets cross section versus boson ${p_{\mathrm{T}}}$ is presented for ${p_{\mathrm{T}}}$ above 200 GeV and compared to the LO and NLO theoretical predictions from MadGraph. A similar measurement of the ${\gamma}$+jets cross section is performed and compared to theoretical predictions from MadGraph and JetPhox . The differential cross section ratio of Z+jets and ${\gamma}$+jets as a function of boson ${p_{\mathrm{T}}}$ is the first measurement of this quantity at 13 TeV at the LHC. The ratio is compared to the NLO calculation from MadGraph and probes boson ${p_{\mathrm{T}}}$ values beyond a TeV. The data is in agreement with the theoretical prediction within uncertainties for the full boson ${p_{\mathrm{T}}}$ range. The measurement of the collinear emission of a Z boson represents the first explicit study of this topology at the LHC. It is accessed by requiring the production of a Z boson in association with at least one very high ${p_{\mathrm{T}}}$ jet (above 300 GeV and 500 GeV) and measuring the differential cross section as a function of the angular separation between the Z boson and the closest jet. The region ${\Delta \text{R}_{Z,\text{closest jet}}} > $ 2.5 is dominated by the back-to-back production of a Z boson and jets while ${\Delta \text{R}_{Z,\text{closest jet}}} < $ 2.5 is enhanced in the collinear production. The unfolded data is compared with the LO and NLO calculations from MadGraph. The NLO MadGraph prediction shows agreement within uncertainties for the bulk of the distribution but underpredicts it for the low ${\Delta \text{R}_{Z,\text{closest jet}}} $ region below 0.8, which is dominated by events with the real emission of a Z boson in close proximity to a jet. Measurements such as the ones presented in this note will become increasingly important in current and future runs of the LHC, where the high center-of-mass energy and larger integrated luminosity will push the LHC physics programme into new territories, necessitating an understanding of standard model processes in regions of previously unexplored parameter space. |
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