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| CMS-PAS-EXO-18-012 | ||
| Search for low mass vector resonances decaying into quark-antiquark pairs with 77.0 fb$^{-1}$ of proton-proton collisions at $\sqrt{s}= $ 13 TeV | ||
| CMS Collaboration | ||
| May 2019 | ||
| Abstract: A search for low mass vector resonances decaying into quark-antiquark pairs is presented. The analysis is based on data collected in proton-proton collisions in 2017 and combined with data collected in 2016 at $\sqrt{s}= $ 13 TeV with the CMS detector at the CERN LHC, corresponding to a total integrated luminosity of 77.0 fb$^{-1}$. Resonance candidates are identified as large-radius jets with two pronged substructure at high transverse momentum. The jet invariant mass spectrum is probed for a potential peak over a smoothly falling background. No evidence for such a resonance is observed within the mass range of 50-450 GeV. Upper limits at the 95% confidence level are set on the mass-coupling parameter space. The 2017 results extend the search region for the first time to masses between 300 GeV and 450 GeV in the boosted regime. | ||
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Links:
CDS record (PDF) ;
CADI line (restricted) ;
These preliminary results are superseded in this paper, PRD 100 (2019) 112007. The superseded preliminary plots can be found here. |
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| Figures | |
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Figure 1:
Trigger efficiency as a function of $m_\text {SD}$ for AK8 jets with ${p_{\mathrm {T}}} > $ 525 GeV (blue) and CA15 jets with ${p_{\mathrm {T}}} > $ 575 GeV (red). The trigger selection is $ > $ 95% efficient for 2017 data for both cone sizes. At high jet masses, the trigger efficiency for the larger CA15 jet decreases slightly. This is due to events for which the offline CA15 jet is not reconstructed as an online AK8 jet, and thus it does not fire triggers with AK8 jet ${p_{\mathrm {T}}}$ and trimmed jet mass thresholds. |
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Figure 2:
The $m_{\text {SD}}$ distribution in data for AK8 jets for each ${p_{\mathrm {T}}}$ category of the fit. Data are shown as black points. The multijet background prediction, including uncertainties, is shown by the shaded bands. Contributions from the W and Z boson, and top quark background processes are shown. A hypothetical Z' boson signal with a mass of 110 GeV is also indicated. The signal is scaled by a factor of 8 for clarity. In the bottom panel, the ratio of the data to its statistical uncertainty, after subtracting the nonresonant backgrounds, is shown. The signal is stacked on top of the peak formed by merged W and Z profiles. |
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Figure 2-a:
The $m_{\text {SD}}$ distribution in data for AK8 jets for the 525-575 GeV ${p_{\mathrm {T}}}$ category of the fit. Data are shown as black points. The multijet background prediction, including uncertainties, is shown by the shaded bands. Contributions from the W and Z boson, and top quark background processes are shown. A hypothetical Z' boson signal with a mass of 110 GeV is also indicated. The signal is scaled by a factor of 8 for clarity. In the bottom panel, the ratio of the data to its statistical uncertainty, after subtracting the nonresonant backgrounds, is shown. The signal is stacked on top of the peak formed by merged W and Z profiles. |
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Figure 2-b:
The $m_{\text {SD}}$ distribution in data for AK8 jets for the 575-625 GeV ${p_{\mathrm {T}}}$ category of the fit. Data are shown as black points. The multijet background prediction, including uncertainties, is shown by the shaded bands. Contributions from the W and Z boson, and top quark background processes are shown. A hypothetical Z' boson signal with a mass of 110 GeV is also indicated. The signal is scaled by a factor of 8 for clarity. In the bottom panel, the ratio of the data to its statistical uncertainty, after subtracting the nonresonant backgrounds, is shown. The signal is stacked on top of the peak formed by merged W and Z profiles. |
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Figure 2-c:
The $m_{\text {SD}}$ distribution in data for AK8 jets for the 625-700 GeV ${p_{\mathrm {T}}}$ category of the fit. Data are shown as black points. The multijet background prediction, including uncertainties, is shown by the shaded bands. Contributions from the W and Z boson, and top quark background processes are shown. A hypothetical Z' boson signal with a mass of 110 GeV is also indicated. The signal is scaled by a factor of 8 for clarity. In the bottom panel, the ratio of the data to its statistical uncertainty, after subtracting the nonresonant backgrounds, is shown. The signal is stacked on top of the peak formed by merged W and Z profiles. |
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Figure 2-d:
The $m_{\text {SD}}$ distribution in data for AK8 jets for the 700-800 GeV ${p_{\mathrm {T}}}$ category of the fit. Data are shown as black points. The multijet background prediction, including uncertainties, is shown by the shaded bands. Contributions from the W and Z boson, and top quark background processes are shown. A hypothetical Z' boson signal with a mass of 110 GeV is also indicated. The signal is scaled by a factor of 8 for clarity. In the bottom panel, the ratio of the data to its statistical uncertainty, after subtracting the nonresonant backgrounds, is shown. The signal is stacked on top of the peak formed by merged W and Z profiles. |
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Figure 2-e:
The $m_{\text {SD}}$ distribution in data for AK8 jets for the 800-1500 GeV ${p_{\mathrm {T}}}$ category of the fit. Data are shown as black points. The multijet background prediction, including uncertainties, is shown by the shaded bands. Contributions from the W and Z boson, and top quark background processes are shown. A hypothetical Z' boson signal with a mass of 110 GeV is also indicated. The signal is scaled by a factor of 8 for clarity. In the bottom panel, the ratio of the data to its statistical uncertainty, after subtracting the nonresonant backgrounds, is shown. The signal is stacked on top of the peak formed by merged W and Z profiles. |
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Figure 3:
The $m_{\text {SD}}$ distribution in data for CA15 jets for the different ${p_{\mathrm {T}}}$ ranges of the fit from 575 to 1500 GeV. Data are shown as black points. The multijet background prediction, including uncertainties, is shown by the shaded bands. Smaller contributions from the W and Z boson, and top quark background processes are shown. A hypothetical Z' boson signal with a mass of 210 GeV is also indicated. The signal is scaled by a factor of 3 for clarity. In the bottom panel, the ratio of the data to its statistical uncertainty, after subtracting the nonresonant backgrounds, is shown. |
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Figure 3-a:
The $m_{\text {SD}}$ distribution in data for CA15 jets for the 575-625 GeV ${p_{\mathrm {T}}}$ range of the fit. Data are shown as black points. The multijet background prediction, including uncertainties, is shown by the shaded bands. Smaller contributions from the W and Z boson, and top quark background processes are shown. A hypothetical Z' boson signal with a mass of 210 GeV is also indicated. The signal is scaled by a factor of 3 for clarity. In the bottom panel, the ratio of the data to its statistical uncertainty, after subtracting the nonresonant backgrounds, is shown. |
png pdf |
Figure 3-b:
The $m_{\text {SD}}$ distribution in data for CA15 jets for the 625-700 GeV ${p_{\mathrm {T}}}$ range of the fit. Data are shown as black points. The multijet background prediction, including uncertainties, is shown by the shaded bands. Smaller contributions from the W and Z boson, and top quark background processes are shown. A hypothetical Z' boson signal with a mass of 210 GeV is also indicated. The signal is scaled by a factor of 3 for clarity. In the bottom panel, the ratio of the data to its statistical uncertainty, after subtracting the nonresonant backgrounds, is shown. |
png pdf |
Figure 3-c:
The $m_{\text {SD}}$ distribution in data for CA15 jets for the 700-800 GeV ${p_{\mathrm {T}}}$ range of the fit. Data are shown as black points. The multijet background prediction, including uncertainties, is shown by the shaded bands. Smaller contributions from the W and Z boson, and top quark background processes are shown. A hypothetical Z' boson signal with a mass of 210 GeV is also indicated. The signal is scaled by a factor of 3 for clarity. In the bottom panel, the ratio of the data to its statistical uncertainty, after subtracting the nonresonant backgrounds, is shown. |
png pdf |
Figure 3-d:
The $m_{\text {SD}}$ distribution in data for CA15 jets for the 800-1500 GeV ${p_{\mathrm {T}}}$ range of the fit. Data are shown as black points. The multijet background prediction, including uncertainties, is shown by the shaded bands. Smaller contributions from the W and Z boson, and top quark background processes are shown. A hypothetical Z' boson signal with a mass of 210 GeV is also indicated. The signal is scaled by a factor of 3 for clarity. In the bottom panel, the ratio of the data to its statistical uncertainty, after subtracting the nonresonant backgrounds, is shown. |
png pdf |
Figure 4:
The upper limits at 95% CL on the quark coupling $g^{\prime}_{\rm q}$ as a function of resonance mass for a leptophobic Z' resonance that only couples to quarks. The result corresponds to data collected in 2017. The observed limits (solid), expected limits (dashed) and their variation at the 1 and 2 standard deviation levels (shaded bands) are shown. The vertical line at 175 GeV corresponds to the transition between the AK8 and CA15 jet selections. |
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Figure 5:
The upper limits at 95% CL on the coupling $g^{\prime}_{\rm q}$ as a function of resonance mass for a leptophobic Z' resonance that only couples to quarks. For masses between 50 and 220 GeV the limits correspond to a Z' resonance reconstructed in AK8 jets using 77.0 fb$^{-1}$ of statistically combined data from 2016 and 2017. The excess in the observed limit over the expected limit near 120 GeV is a remnant of the analysis of the data collected in 2016. For masses above 220 GeV up to 450 GeV the results correspond to a Z' resonance reconstructed in CA15 jets using 41.1 fb$^{-1}$ of data collected in 2017. |
| Tables | |
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Table 1:
Summary of the systematic uncertainties for signal (\mathrm{Z'}) and \mathrm{W} /\mathrm{Z} background processes. The reported ranges denote a variation of the uncertainty across $ {p_{\mathrm {T}}} $ bins, from 525 to 1500 GeV (AK8 jets) and from 575 to 1500 GeV (CA15 jets). The symbol $^\triangle $ denotes uncorrelated uncertainties for each $ {p_{\mathrm {T}}} $ bin. For the uncertainties related to the jet mass scale and resolution, the reported percentage reflects a one standard deviation effect on the nominal jet mass shape. A long dash ({\text {--}}) indicates that the uncertainty does not apply. |
| Summary |
| A search for a vector resonance (Z') decaying into a quark-antiquark pair and reconstructed as a single jet was presented, using a data set comprised of proton-proton collisions at $\sqrt{s} = $ 13 TeV collected in 2017 at the CERN LHC, corresponding to an integrated luminosity of 41.1 fb$^{-1}$. The results are statistically combined with those obtained with data collected in 2016 to achieve more sensitive exclusion limits with a total integrated luminosity of 77.0 fb$^{-1}$. Jet substructure techniques are employed to identify a jet containing a Z' boson candidate over a smoothly falling soft-drop jet mass distribution in data. No significant excess above the SM prediction is observed. Upper limits at a 95% confidence level are set on the Z' boson coupling to quarks, $g^{\prime}_{\rm q}$, as a function of the Z' boson mass. Coupling values of $g^{\prime}_{\rm q} > $ 0.4 are excluded over the Z' mass range from 50 to 450 GeV, with strong constraints for masses less than 200 GeV The results obtained for masses from 300 to 450 GeV represent the first direct limits to be published in this range for a leptophobic Z' signal reconstructed as a single large-radius jet. |
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