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| CMS-EXO-16-057 ; CERN-EP-2018-007 | ||
| Search for narrow resonances in the b-tagged dijet mass spectrum in proton-proton collisions at $\sqrt{s} = $ 8 TeV | ||
| CMS Collaboration | ||
| 17 February 2018 | ||
| Phys. Rev. Lett. 120 (2018) 201801 | ||
| Abstract: A search for narrow resonances decaying to bottom quark-antiquark pairs is presented, using a data sample of proton-proton collisions at $\sqrt{s} = $ 8 TeV corresponding to an integrated luminosity of 19.7 fb$^{-1}$. The search is extended to masses lower than those reached in typical searches for resonances decaying into jet pairs at the LHC, by taking advantage of triggers that identify jets originating from bottom quarks. No significant excess of events is observed above the background predictions. Limits are set on the product of cross section and branching fraction to bottom quarks for spin 0, 1, and 2 resonances in the mass range of 325-1200 GeV. These results significantly improve on the limits for resonances decaying into jet pairs in the 325-500 GeV mass range. | ||
| Links: e-print arXiv:1802.06149 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
The products of acceptance and efficiency for simulated signal events in SR1 and SR2, separately for the scalar, Z', and RS graviton signal models. The shaded bands represent the statistical uncertainties. |
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Figure 2:
The dijet invariant mass distributions in SR1 (left) and SR2 (right), shown with the background prediction derived from a fit using an empirical function under the background-only hypothesis. Representative examples of signal distributions are also shown, each normalized to a visible cross section of 1 pb. The bottom panels show the difference between the data and the background estimate, divided by the statistical uncertainty in the estimated background. |
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Figure 2-a:
The dijet invariant mass distribution in SR1, shown with the background prediction derived from a fit using an empirical function under the background-only hypothesis. Representative examples of signal distributions are also shown, each normalized to a visible cross section of 1 pb. The bottom panel shows the difference between the data and the background estimate, divided by the statistical uncertainty in the estimated background. |
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Figure 2-b:
The dijet invariant mass distribution in SR2, shown with the background prediction derived from a fit using an empirical function under the background-only hypothesis. Representative examples of signal distributions are also shown, each normalized to a visible cross section of 1 pb. The bottom panel shows the difference between the data and the background estimate, divided by the statistical uncertainty in the estimated background. |
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Figure 3:
Observed and expected 95% CL upper limits on the product of cross section and branching fraction to bottom quark-antiquark pairs for a scalar resonance (left), Z' boson (middle), and RS graviton (right) signal models, as functions of resonance mass. The discontinuity in the limits at 700 GeV is associated with a change in the acceptance from SR1 to SR2. |
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Figure 3-a:
Observed and expected 95% CL upper limits on the product of cross section and branching fraction to bottom quark-antiquark pairs for a scalar resonance signal model, as functions of resonance mass. The discontinuity in the limits at 700 GeV is associated with a change in the acceptance from SR1 to SR2. |
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Figure 3-b:
Observed and expected 95% CL upper limits on the product of cross section and branching fraction to bottom quark-antiquark pairs for a Z' boson signal model, as functions of resonance mass. The discontinuity in the limits at 700 GeV is associated with a change in the acceptance from SR1 to SR2. |
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Figure 3-c:
Observed and expected 95% CL upper limits on the product of cross section and branching fraction to bottom quark-antiquark pairs for a RS graviton signal model, as functions of resonance mass. The discontinuity in the limits at 700 GeV is associated with a change in the acceptance from SR1 to SR2. |
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Figure 4:
Left: The 95% CL upper limits (solid line) on the universal coupling ${g'_ {\mathrm {q}}} $ between the leptophobic Z' boson and quarks. Limits from other experiments [2,8,9,18] and earlier CMS analyses [33,34,37], are also shown, along with an indirect constraint from the Z boson width [74]. Right: Expected (dashed lines) and observed (solid lines) 95% CL upper limits on the simplified model variable $\zeta $. The limits are shown for $ {\mathrm {u}} {\overline {\mathrm {u}}} \to {\mathrm {Z}'}$ and $ {\mathrm {d}} {\overline {\mathrm {d}}} \to {\mathrm {Z}'}$ individually, as well as for $ {\mathrm {p}} {\mathrm {p}}\to {\mathrm {Z}'}$, assuming a universal quark coupling. The $\zeta $ values for the Z' boson model with $ {g'_ {\mathrm {q}}} = $ 0.25 are also shown. The hatched red band represents the envelope of limits for theoretical models that predict an $s$-channel production of a Z' resonance with arbitrary couplings to up and down quarks. The discontinuity in the limits at 700 GeV is associated with a change in the acceptance from SR1 to SR2. |
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Figure 4-a:
The 95% CL upper limits (solid line) on the universal coupling ${g'_ {\mathrm {q}}} $ between the leptophobic Z' boson and quarks. Limits from other experiments [2,8,9,18] and earlier CMS analyses [33,34,37], are also shown, along with an indirect constraint from the Z boson width [74]. The discontinuity in the limits at 700 GeV is associated with a change in the acceptance from SR1 to SR2. |
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Figure 4-b:
Expected (dashed lines) and observed (solid lines) 95% CL upper limits on the simplified model variable $\zeta $. The limits are shown for $ {\mathrm {u}} {\overline {\mathrm {u}}} \to {\mathrm {Z}'}$ and $ {\mathrm {d}} {\overline {\mathrm {d}}} \to {\mathrm {Z}'}$ individually, as well as for $ {\mathrm {p}} {\mathrm {p}}\to {\mathrm {Z}'}$, assuming a universal quark coupling. The $\zeta $ values for the Z' boson model with $ {g'_ {\mathrm {q}}} = $ 0.25 are also shown. The hatched red band represents the envelope of limits for theoretical models that predict an $s$-channel production of a Z' resonance with arbitrary couplings to up and down quarks. The discontinuity in the limits at 700 GeV is associated with a change in the acceptance from SR1 to SR2. |
| Summary |
| In summary, a search for new resonances decaying to bottom quark-antiquark pairs produced in 8 TeV proton-proton collisions has been presented. Using triggers that identify jets originating from bottom quarks, the search probes signal masses as low as 325 GeV. No statistically significant excesses above the background predictions are observed in the entire invariant mass range studied, 325--1200 GeV. Upper limits are set on the production cross section of scalar, vector, and tensor resonances. The limits are also interpreted in the context of a simplified model of a leptophobic Z' boson with a universal coupling ${g'_ {\mathrm {q}}} $ to quarks. Values of ${g'_ {\mathrm {q}}} $ above 0.11--0.18 are excluded for Z' boson masses below 500 GeV, improving on the previous best limits in this mass range, which date back to the CDF experiment. The first experimental limits on the parameter $\zeta$ of a simplified $s$-channel resonance framework [80] have been obtained, making possible the reinterpretation of the limits in a variety of theoretical models corresponding to different resonance production and decay mechanisms. |
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