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| CMS-EXO-15-005 ; CERN-EP-2016-209 | ||
| Search for narrow resonances in dilepton mass spectra in proton-proton collisions at $ \sqrt{s} = $ 13 TeV and combination with 8 TeV data | ||
| CMS Collaboration | ||
| 18 September 2016 | ||
| Phys. Lett. B 768 (2017) 57 | ||
| Abstract: A search for narrow resonances in dielectron and dimuon invariant mass spectra has been performed using data obtained from proton-proton collisions at $ \sqrt{s} = $ 13 TeV collected with the CMS detector. The integrated luminosity for the dielectron sample is 2.7 fb$^{-1}$ and for the dimuon sample 2.9 fb$^{-1}$. The sensitivity of the search is increased by combining these data with a previously analysed set of data obtained at $ \sqrt{s} = $ 8 TeV and corresponding to a luminosity of 20 fb$^{-1}$. No evidence for non-standard-model physics is found, either in the 13 TeV data set alone, or in the combined data set. Upper limits on the product of production cross section and branching fraction have also been calculated in a model-independent manner to enable interpretation in models predicting a narrow dielectron or dimuon resonance structure. Limits are set on the masses of hypothetical particles that could appear in new-physics scenarios. For the $\mathrm{Z}'_{\text{SSM}}$ particle, which arises in the sequential standard model, and for the superstring inspired $\mathrm{Z}'_{\psi}$ particle, 95% confidence level lower mass limits for the combined data sets and combined channels are found to be 3.37 and 2.82 TeV, respectively. The corresponding limits for Kaluza-Klein gravitons arising in the Randall-Sundrum model of extra dimensions with coupling parameters 0.01 and 0.10 are 1.46 and 3.11 TeV, respectively. These results significantly extend previous limits. | ||
| Links: e-print arXiv:1609.05391 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; CADI line (restricted) ; | ||
| Figures | |
png pdf |
Figure 1:
The invariant mass spectrum of (left) dielectron and (right) dimuon events at $ \sqrt{s} = $ 13 TeV. The points with error bars represent the data. The histograms represent the expectations from SM processes. The bins have equal width in logarithmic scale but the width in GeV becomes larger with increasing mass. Example signal shapes for a narrow resonance with a mass of 2 TeV are shown by the stacked open histograms. |
png pdf |
Figure 1-a:
The invariant mass spectrum of dielectron events at $ \sqrt{s} = $ 13 TeV. The points with error bars represent the data. The histograms represent the expectations from SM processes. The bins have equal width in logarithmic scale but the width in GeV becomes larger with increasing mass. Example signal shapes for a narrow resonance with a mass of 2 TeV are shown by the stacked open histograms. |
png pdf |
Figure 1-b:
The invariant mass spectrum of dimuon events at $ \sqrt{s} = $ 13 TeV. The points with error bars represent the data. The histograms represent the expectations from SM processes. The bins have equal width in logarithmic scale but the width in GeV becomes larger with increasing mass. Example signal shapes for a narrow resonance with a mass of 2 TeV are shown by the stacked open histograms. |
png pdf |
Figure 2:
The 95% CL upper limits on the product of production cross section and branching fraction for a spin-1 resonance with a width equal to 0.6% of the resonance mass, relative to the product of production cross section and branching fraction for a Z boson, for the (left) dielectron and (right) dimuon channels in the 13 TeV data. The shaded bands correspond to the 68 and 95% quantiles for the expected limits. Theoretical predictions for the spin-1 $\mathrm{Z}'_{\text{SSM}}$ and $\mathrm{Z}'_{\psi}$ resonances are shown for comparison. |
png pdf |
Figure 2-a:
The 95% CL upper limits on the product of production cross section and branching fraction for a spin-1 resonance with a width equal to 0.6% of the resonance mass, relative to the product of production cross section and branching fraction for a Z boson, for the dielectron channel in the 13 TeV data. The shaded bands correspond to the 68 and 95% quantiles for the expected limits. Theoretical predictions for the spin-1 $\mathrm{Z}'_{\text{SSM}}$ and $\mathrm{Z}'_{\psi}$ resonances are shown for comparison. |
png pdf |
Figure 2-b:
The 95% CL upper limits on the product of production cross section and branching fraction for a spin-1 resonance with a width equal to 0.6% of the resonance mass, relative to the product of production cross section and branching fraction for a Z boson, for the dimuon channel in the 13 TeV data. The shaded bands correspond to the 68 and 95% quantiles for the expected limits. Theoretical predictions for the spin-1 $\mathrm{Z}'_{\text{SSM}}$ and $\mathrm{Z}'_{\psi}$ resonances are shown for comparison. |
png pdf |
Figure 3:
The 95% CL upper limits on the product of production cross section and branching fraction for a spin-1 resonance for widths equal to 0, 0.6, and 3.0% of the resonance mass, relative to the product of production cross section and branching fraction for a Z boson, for the (left) dielectron and (right) dimuon channels in the 13 TeV data. Theoretical predictions for the spin-1 $\mathrm{Z}'_{\text{SSM}}$ and $\mathrm{Z}'_{\psi}$ resonances are also shown. |
png pdf |
Figure 3-a:
The 95% CL upper limits on the product of production cross section and branching fraction for a spin-1 resonance for widths equal to 0, 0.6, and 3.0% of the resonance mass, relative to the product of production cross section and branching fraction for a Z boson, for the dielectron channel in the 13 TeV data. Theoretical predictions for the spin-1 $\mathrm{Z}'_{\text{SSM}}$ and $\mathrm{Z}'_{\psi}$ resonances are also shown. |
png pdf |
Figure 3-b:
The 95% CL upper limits on the product of production cross section and branching fraction for a spin-1 resonance for widths equal to 0, 0.6, and 3.0% of the resonance mass, relative to the product of production cross section and branching fraction for a Z boson, for the dimuon channel in the 13 TeV data. Theoretical predictions for the spin-1 $\mathrm{Z}'_{\text{SSM}}$ and $\mathrm{Z}'_{\psi}$ resonances are also shown. |
png pdf |
Figure 4:
The 95% CL upper limits on the product of production cross section and branching fraction for a spin-1 resonance, relative to the product of production cross section and branching fraction for a Z boson, for the combined dielectron and dimuon channels in the 13 TeV data, (left) for a resonance width equal to 0.6% of the resonance mass and (right) for resonance widths equal to 0, 0.6, and 3.0% of the resonance mass. The shaded bands correspond to the 68 and 95% quantiles for the expected limits. Theoretical predictions for the spin-1 $\mathrm{Z}'_{\text{SSM}}$ and $\mathrm{Z}'_{\psi}$ resonances are also shown. |
png pdf |
Figure 4-a:
The 95% CL upper limits on the product of production cross section and branching fraction for a spin-1 resonance, relative to the product of production cross section and branching fraction for a Z boson, for the combined dielectron and dimuon channels in the 13 TeV data, for a resonance width equal to 0.6% of the resonance mass. The shaded bands correspond to the 68 and 95% quantiles for the expected limits. Theoretical predictions for the spin-1 $\mathrm{Z}'_{\text{SSM}}$ and $\mathrm{Z}'_{\psi}$ resonances are also shown. |
png pdf |
Figure 4-b:
The 95% CL upper limits on the product of production cross section and branching fraction for a spin-1 resonance, relative to the product of production cross section and branching fraction for a Z boson, for the combined dielectron and dimuon channels in the 13 TeV data, for resonance widths equal to 0, 0.6, and 3.0% of the resonance mass. Theoretical predictions for the spin-1 $\mathrm{Z}'_{\text{SSM}}$ and $\mathrm{Z}'_{\psi}$ resonances are also shown. |
png pdf |
Figure 5:
The 95% CL upper limits on the product of production cross section and branching fraction for a spin-1 resonance with a width equal to 0.6% of the resonance mass, relative to the product of production cross section and branching fraction for a Z boson, for the combined 8 and 13 TeV data in the (left) dielectron and (right) dimuon channel. The shaded bands correspond to the 68 and 95% quantiles for the expected limits. Theoretical predictions for the spin-1 $\mathrm{Z}'_{\text{SSM}}$ and $\mathrm{Z}'_{\psi}$ resonances are also shown. |
png pdf |
Figure 5-a:
The 95% CL upper limits on the product of production cross section and branching fraction for a spin-1 resonance with a width equal to 0.6% of the resonance mass, relative to the product of production cross section and branching fraction for a Z boson, for the combined 8 and 13 TeV data in the dielectron channel. The shaded bands correspond to the 68 and 95% quantiles for the expected limits. Theoretical predictions for the spin-1 $\mathrm{Z}'_{\text{SSM}}$ and $\mathrm{Z}'_{\psi}$ resonances are also shown. |
png pdf |
Figure 5-b:
The 95% CL upper limits on the product of production cross section and branching fraction for a spin-1 resonance with a width equal to 0.6% of the resonance mass, relative to the product of production cross section and branching fraction for a Z boson, for the combined 8 and 13 TeV data in the dimuon channel. The shaded bands correspond to the 68 and 95% quantiles for the expected limits. Theoretical predictions for the spin-1 $\mathrm{Z}'_{\text{SSM}}$ and $\mathrm{Z}'_{\psi}$ resonances are also shown. |
png pdf |
Figure 6:
The 95% CL upper limits on the product of production cross section and branching fraction for (left) a spin-1 resonance with a width equal to 0.6% of the resonance mass and (right) for a spin-2 RS graviton, both relative to the product of production cross section and branching fraction for a Z boson, for the combined dielectron and dimuon channels and combined 8 and 13 TeV data. For the spin-1 results (left plot), the shaded bands correspond to the 68 and 95% quantiles for the expected limits, and theoretical predictions are shown for the spin-1 $\mathrm{Z}'_{\text{SSM}}$ and $\mathrm{Z}'_{\psi}$ resonances. For the spin-2 results (right plot), observed limits, expected limits, and theoretical predictions are shown for values of the coupling parameter $k/\overline {M}_\mathrm {Pl}= $ 0.01 and 0.10. |
png pdf |
Figure 6-a:
The 95% CL upper limits on the product of production cross section and branching fraction for a spin-1 resonance with a width equal to 0.6% of the resonance mass, relative to the product of production cross section and branching fraction for a Z boson, for the combined dielectron and dimuon channels and combined 8 and 13 TeV data. The shaded bands correspond to the 68 and 95% quantiles for the expected limits, and theoretical predictions are shown for the spin-1 $\mathrm{Z}'_{\text{SSM}}$ and $\mathrm{Z}'_{\psi}$ resonances. |
png pdf |
Figure 6-b:
The 95% CL upper limits on the product of production cross section and branching fraction for a spin-2 RS graviton, relative to the product of production cross section and branching fraction for a Z boson, for the combined dielectron and dimuon channels and combined 8 and 13 TeV data. Observed limits, expected limits, and theoretical predictions are shown for values of the coupling parameter $k/\overline {M}_\mathrm {Pl}= $ 0.01 and 0.10. |
| Tables | |
png pdf |
Table 1:
The observed and expected 95% CL lower limits on the masses of spin-1 $\mathrm{Z}'_{\text{SSM}}$ and $\mathrm{Z}'_{\psi}$ bosons for the combination of the 8 and 13 TeV data, assuming a signal width of 0.6% of the resonance mass for $\mathrm{Z}'_{\psi}$ and 3% for $\mathrm{Z}'_{\text{SSM}}$ . |
png pdf |
Table 2:
The observed and expected 95% CL lower limits on the masses of spin-2 Kaluza-Klein gravitons in the Randall-Sundrum model, for two values of the coupling parameter, $k/\overline {M}_\mathrm {Pl}$. |
| Summary |
| A search for narrow resonances in dielectron and dimuon invariant mass spectra has been performed using data obtained from proton-proton collisions at $ \sqrt{s} = $ 13 TeV. The integrated luminosity for the dielectron sample is 2.7 fb$^{-1}$ and for the dimuon sample 2.9 fb$^{-1}$. The sensitivity of the search is increased by combining these data with a previously analysed set of data obtained at $ \sqrt{s} = $ 8 TeV and corresponding to a luminosity of 20 fb$^{-1}$. No evidence for non-standard-model physics is found, either in the 13 TeV data set alone, or in the combined data set. Upper limits at 95% confidence level on the product of production cross section and branching fraction have also been calculated in a model-independent manner to enable interpretation in models predicting a narrow dielectron or dimuon resonance structure. Limits are set on the masses of hypothetical particles that could appear in new-physics scenarios. For the $\mathrm{Z}'_{\text{SSM}}$ particle, which arises in the sequential standard model, and for the superstring inspired $\mathrm{Z}'_{\psi}$ particle, 95% confidence level lower mass limits for the combined data sets and combined channels are found to be 3.37 and 2.82 TeV, respectively. The corresponding limits for Kaluza-Klein gravitons arising in the Randall-Sundrum model of extra dimensions with coupling parameters 0.01 and 0.10 are 1.46 and 3.11 TeV, respectively. These results significantly extend previous limits. |
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