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| CMS-SMP-14-004 ; CERN-PH-EP-2015-295 | ||
| Forward-backward asymmetry of Drell-Yan lepton pairs in pp collisions at $\sqrt{s} = $ 8 TeV | ||
| CMS Collaboration | ||
| 18 January 2016 | ||
| Eur. Phys. J. C 76 (2016) 325 | ||
| Abstract: A measurement of the forward-backward asymmetry $A_{\mathrm{FB}}$ of oppositely charged lepton pairs ($\mu\mu$ and $\mathrm{ e }\mathrm{ e }$) produced via $\mathrm{Z}/\gamma^*$ boson exchange in pp collisions at $\sqrt{s} = $ 8 TeV is presented. The data sample corresponds to an integrated luminosity of 19.7 fb$^{-1}$ collected with the CMS detector at the LHC. The measurement of $A_{\mathrm{FB}}$ is performed for dilepton masses between 40 GeV and 2 TeV and for dilepton rapidity up to 5. The $A_{\mathrm{FB}}$ measurements as a function of dilepton mass and rapidity are compared with the standard model predictions. | ||
| Links: e-print arXiv:1601.04768 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1-a:
The invariant mass distributions for $\mu \mu $ (a), $\mathrm{ e } \mathrm{ e } $ (b) events with $ {| y | }< $ 2.4, and $\mathrm{ e } \mathrm{ e } $ (c) events with 2.4 $ < {| y | }< $ 5. Only statistical uncertainties are shown. The stacked histograms represent the sum of the background contributions and the signal. |
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Figure 1-b:
The invariant mass distributions for $\mu \mu $ (a), $\mathrm{ e } \mathrm{ e } $ (b) events with $ {| y | }< $ 2.4, and $\mathrm{ e } \mathrm{ e } $ (c) events with 2.4 $ < {| y | }< $ 5. Only statistical uncertainties are shown. The stacked histograms represent the sum of the background contributions and the signal. |
png pdf |
Figure 1-c:
The invariant mass distributions for $\mu \mu $ (a), $\mathrm{ e } \mathrm{ e } $ (b) events with $ {| y | }< $ 2.4, and $\mathrm{ e } \mathrm{ e } $ (c) events with 2.4 $ < {| y | }< $ 5. Only statistical uncertainties are shown. The stacked histograms represent the sum of the background contributions and the signal. |
png pdf |
Figure 2-a:
The $\cos\theta ^{*}_\mathrm {CS}$ distributions for $\mu \mu $ ($\mathrm{ e } \mathrm{ e } $) events are presented in the a,b (c,d) panels. Only statistical uncertainties are shown. The stacked histograms represent the sum of the background contribution and the signal. The plots on the a,c (b,d) panels correspond to events with dilepton invariant mass 50 $ < M < $ 60 GeV (133 $ < M < $ 150 GeV ). |
png pdf |
Figure 2-b:
The $\cos\theta ^{*}_\mathrm {CS}$ distributions for $\mu \mu $ ($\mathrm{ e } \mathrm{ e } $) events are presented in the a,b (c,d) panels. Only statistical uncertainties are shown. The stacked histograms represent the sum of the background contribution and the signal. The plots on the a,c (b,d) panels correspond to events with dilepton invariant mass 50 $ < M < $ 60 GeV (133 $ < M < $ 150 GeV ). |
png pdf |
Figure 2-c:
The $\cos\theta ^{*}_\mathrm {CS}$ distributions for $\mu \mu $ ($\mathrm{ e } \mathrm{ e } $) events are presented in the a,b (c,d) panels. Only statistical uncertainties are shown. The stacked histograms represent the sum of the background contribution and the signal. The plots on the a,c (b,d) panels correspond to events with dilepton invariant mass 50 $ < M < $ 60 GeV (133 $ < M < $ 150 GeV ). |
png pdf |
Figure 2-d:
The $\cos\theta ^{*}_\mathrm {CS}$ distributions for $\mu \mu $ ($\mathrm{ e } \mathrm{ e } $) events are presented in the a,b (c,d) panels. Only statistical uncertainties are shown. The stacked histograms represent the sum of the background contribution and the signal. The plots on the a,c (b,d) panels correspond to events with dilepton invariant mass 50 $ < M < $ 60 GeV (133 $ < M < $ 150 GeV ). |
png pdf |
Figure 3-a:
The unfolded ${A_\mathrm {FB}}$ distributions for muons (open squares) and electrons (solid circles) for the four central rapidity regions. The statistical (thick vertical bar) and statistical plus systematics (thin vertical bar) uncertainties are presented. The solid circles are shifted slightly to compare the result better. The lower panel in each plot shows the difference of the unfolded ${A_\mathrm {FB}}$ in muons and electrons divided by the total uncertainty (stat. $\oplus $ syst.). |
png pdf |
Figure 3-b:
The unfolded ${A_\mathrm {FB}}$ distributions for muons (open squares) and electrons (solid circles) for the four central rapidity regions. The statistical (thick vertical bar) and statistical plus systematics (thin vertical bar) uncertainties are presented. The solid circles are shifted slightly to compare the result better. The lower panel in each plot shows the difference of the unfolded ${A_\mathrm {FB}}$ in muons and electrons divided by the total uncertainty (stat. $\oplus $ syst.). |
png pdf |
Figure 3-c:
The unfolded ${A_\mathrm {FB}}$ distributions for muons (open squares) and electrons (solid circles) for the four central rapidity regions. The statistical (thick vertical bar) and statistical plus systematics (thin vertical bar) uncertainties are presented. The solid circles are shifted slightly to compare the result better. The lower panel in each plot shows the difference of the unfolded ${A_\mathrm {FB}}$ in muons and electrons divided by the total uncertainty (stat. $\oplus $ syst.). |
png pdf |
Figure 3-d:
The unfolded ${A_\mathrm {FB}}$ distributions for muons (open squares) and electrons (solid circles) for the four central rapidity regions. The statistical (thick vertical bar) and statistical plus systematics (thin vertical bar) uncertainties are presented. The solid circles are shifted slightly to compare the result better. The lower panel in each plot shows the difference of the unfolded ${A_\mathrm {FB}}$ in muons and electrons divided by the total uncertainty (stat. $\oplus $ syst.). |
png pdf |
Figure 4-a:
The combined ($\mu^+ \mu^- $ and $\mathrm{ e }^- \mathrm{ e }^+ $ ) unfolded ${A_\mathrm {FB}}$ distributions in the four central rapidity regions. The statistical (thick vertical bar) and statistical plus systematics (thin vertical bar) uncertainties are presented. The measurements are compared with the prediction of POWHEG. The total uncertainties (considering the statistical, PDF, and scale uncertainties) in the POWHEG prediction are shown as shaded bands. The lower panel in each plot shows the difference of ${A_\mathrm {FB}}$ in data and prediction divided by the total uncertainty of data and prediction. |
png pdf |
Figure 4-b:
The combined ($\mu^+ \mu^- $ and $\mathrm{ e }^- \mathrm{ e }^+ $ ) unfolded ${A_\mathrm {FB}}$ distributions in the four central rapidity regions. The statistical (thick vertical bar) and statistical plus systematics (thin vertical bar) uncertainties are presented. The measurements are compared with the prediction of POWHEG. The total uncertainties (considering the statistical, PDF, and scale uncertainties) in the POWHEG prediction are shown as shaded bands. The lower panel in each plot shows the difference of ${A_\mathrm {FB}}$ in data and prediction divided by the total uncertainty of data and prediction. |
png pdf |
Figure 4-c:
The combined ($\mu^+ \mu^- $ and $\mathrm{ e }^- \mathrm{ e }^+ $ ) unfolded ${A_\mathrm {FB}}$ distributions in the four central rapidity regions. The statistical (thick vertical bar) and statistical plus systematics (thin vertical bar) uncertainties are presented. The measurements are compared with the prediction of POWHEG. The total uncertainties (considering the statistical, PDF, and scale uncertainties) in the POWHEG prediction are shown as shaded bands. The lower panel in each plot shows the difference of ${A_\mathrm {FB}}$ in data and prediction divided by the total uncertainty of data and prediction. |
png pdf |
Figure 4-d:
The combined ($\mu^+ \mu^- $ and $\mathrm{ e }^- \mathrm{ e }^+ $ ) unfolded ${A_\mathrm {FB}}$ distributions in the four central rapidity regions. The statistical (thick vertical bar) and statistical plus systematics (thin vertical bar) uncertainties are presented. The measurements are compared with the prediction of POWHEG. The total uncertainties (considering the statistical, PDF, and scale uncertainties) in the POWHEG prediction are shown as shaded bands. The lower panel in each plot shows the difference of ${A_\mathrm {FB}}$ in data and prediction divided by the total uncertainty of data and prediction. |
png pdf |
Figure 5:
The unfolded ${A_\mathrm {FB}}$ distribution for the forward rapidity region (2.4 $ < {| y | }< $ 5 ) using one central electron ($ {| \eta | }< $ 2.4 ) and one HF electron (3 $ < {| \eta | }< $ 5 ). The inner thick vertical bars correspond to the statistical uncertainty and the outer thin vertical bars to the total uncertainties. The measurements are compared with the prediction of POWHEG. The total uncertainties (considering the statistical, PDF, and scale uncertainties) in the POWHEG prediction are shown as shaded bands. The lower panel shows the difference of ${A_\mathrm {FB}}$ in data and prediction divided by the total uncertainty of data and prediction. |
| Tables | |
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Table 1:
The maximum value of the systematic uncertainty in ${A_\mathrm {FB}}$ as a function of $M$ from each source for different regions of $ {| y | }$. |
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Table 2:
The combined ($\mathrm{ e } \mathrm{ e } $ and $\mu \mu $) ${A_\mathrm {FB}}$ measurements, with statistical and systematic uncertainties for the four rapidity regions with $ {| y | }< $ 2.4. The ${A_\mathrm {FB}}$ quantity for $\mathrm{ e } \mathrm{ e } $ events is also shown for 2.4 $ < {| y | }< $ 5. |
| Summary |
| We report a measurement of the forward-backward asymmetry of oppositely charged $\mu\mu$ and $\mathrm{ e }\mathrm{ e }$ pairs produced via a $\mathrm{Z}/\gamma^*$ boson exchange at $\sqrt{s} = $ 8 TeV with a data sample corresponding to an integrated luminosity of 19.7 fb$^{-1}$. The $A_{\mathrm{FB}}$ measurement is performed as a function of the dilepton invariant mass between 40 GeV and 2 TeV for $\mu\mu$ and $\mathrm{ e }\mathrm{ e }$ events in 4 dilepton rapidity bins up to $| y | = $ 2.4. For $\mathrm{ e }\mathrm{ e }$ events with 2.4 $ < | y | < $ 5, the $A_{\mathrm{FB}}$ measurement is performed for dielectron masses between 40 and 320 GeV. The large data sample collected at 8 TeV extends the measurement of $A_{\mathrm{FB}}$ in the high mass region compared to previous results. The final $A_{\mathrm{FB}}$ values are corrected for detector resolution, acceptance, and final state radiation effects. The measurements of $A_{\mathrm{FB}}$M are consistent with standard model predictions. |
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