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| CMS-EXO-20-007 ; CERN-EP-2021-238 | ||
| Search for high-mass resonances decaying to a jet and a Lorentz-boosted resonance in proton-proton collisions at $\sqrt{s} = $ 13 TeV | ||
| CMS Collaboration | ||
| 6 January 2022 | ||
| Phys. Lett. B 832 (2022) 137263 | ||
| Abstract: A search is reported for high-mass hadronic resonances that decay to a parton and a Lorentz-boosted resonance, which in turn decays into a pair of partons. The search is based on data collected with the CMS detector at the LHC in proton-proton collisions at $\sqrt{s} = $ 13 TeV, corresponding to an integrated luminosity of 138 fb$^{-1}$. The boosted resonance is reconstructed as a single wide jet with substructure consistent with a two-body decay. The high-mass resonance is thus considered as a dijet system. The jet substructure information and the kinematic properties of cascade resonance decays are exploited to disentangle the signal from the large quantum chromodynamics multijet background. The dijet mass spectrum is analyzed for the presence of new high-mass resonances, and is found to be consistent with the standard model background predictions. Results are interpreted in a warped extra dimension model where the high-mass resonance is a Kaluza-Klein gluon, the boosted resonance is a radion, and the final state partons are all gluons. Limits on the production cross section are set as a function of the Kaluza-Klein gluon and radion masses. These limits exclude at 95% confidence level models with Kaluza-Klein gluon masses in the range from 2.0 to 4.3 TeV and radion masses in the range from 0.20 to 0.74 TeV. By exploring a novel experimental signature, the observed limits on the Kaluza-Klein gluon mass are extended by up to about 1 TeV compared to previous searches. | ||
| Links: e-print arXiv:2201.02140 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; | ||
| Figures | Summary | Additional Figures | References | CMS Publications |
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| Figures | |
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Figure 1:
Feynman diagram of leading order production of the process $ {\mathrm {R}_1} \to {\mathrm {R}_2} + {\mathrm {P}_3} \to ({\mathrm {P}_1} + {\mathrm {P}_2}) + {\mathrm {P}_3} $ involving cascade decays of two new massive resonances ${\mathrm {R}_1}$ and ${\mathrm {R}_2}$ to partons ${\mathrm {P}_1}$, ${\mathrm {P}_2}$, and ${\mathrm {P}_3}$ in the final state. |
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Figure 2:
In the simulation, reconstructed mass of the ${\mathrm {R}_2}$ jet candidate vs. the reconstructed mass of the ${\mathrm {P}_3}$ jet candidate (points) for ${\mathrm {R}_1}$ resonance events originating from two different mass hypotheses. The left plot is for a ${\mathrm {G}_{\mathrm {KK}}}$ with a mass $ {m\, ( {\mathrm {G}_{\mathrm {KK}}} ) } = {m\, ( {\mathrm {R}_1} ) } = $ 4 TeV, decaying to a radion with a mass $ {m\, ( \phi ) } = {m\, ( {\mathrm {R}_2} ) } = $ 0.4 TeV and a gluon. The 22 event categories in this plane, within which the search in the dijet mass distribution is conducted, are shown with red boxes. The right plot is for the same decay sequence, with masses $ {m\, ( {\mathrm {G}_{\mathrm {KK}}} ) } = $ 5 TeV and $ {m\, ( \phi ) } = $ 1 TeV, for which the number of event categories is 9. For both plots, the cross-like shape is approximately centered on the second resonance pole mass ${m\, ( {\mathrm {R}_2} ) }$ for both the horizontal and the vertical axes. |
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Figure 2-a:
In the simulation, reconstructed mass of the ${\mathrm {R}_2}$ jet candidate vs. the reconstructed mass of the ${\mathrm {P}_3}$ jet candidate (points) for ${\mathrm {R}_1}$ resonance events originating from two different mass hypotheses. The left plot is for a ${\mathrm {G}_{\mathrm {KK}}}$ with a mass $ {m\, ( {\mathrm {G}_{\mathrm {KK}}} ) } = {m\, ( {\mathrm {R}_1} ) } = $ 4 TeV, decaying to a radion with a mass $ {m\, ( \phi ) } = {m\, ( {\mathrm {R}_2} ) } = $ 0.4 TeV and a gluon. The 22 event categories in this plane, within which the search in the dijet mass distribution is conducted, are shown with red boxes. The right plot is for the same decay sequence, with masses $ {m\, ( {\mathrm {G}_{\mathrm {KK}}} ) } = $ 5 TeV and $ {m\, ( \phi ) } = $ 1 TeV, for which the number of event categories is 9. For both plots, the cross-like shape is approximately centered on the second resonance pole mass ${m\, ( {\mathrm {R}_2} ) }$ for both the horizontal and the vertical axes. |
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Figure 2-b:
In the simulation, reconstructed mass of the ${\mathrm {R}_2}$ jet candidate vs. the reconstructed mass of the ${\mathrm {P}_3}$ jet candidate (points) for ${\mathrm {R}_1}$ resonance events originating from two different mass hypotheses. The left plot is for a ${\mathrm {G}_{\mathrm {KK}}}$ with a mass $ {m\, ( {\mathrm {G}_{\mathrm {KK}}} ) } = {m\, ( {\mathrm {R}_1} ) } = $ 4 TeV, decaying to a radion with a mass $ {m\, ( \phi ) } = {m\, ( {\mathrm {R}_2} ) } = $ 0.4 TeV and a gluon. The 22 event categories in this plane, within which the search in the dijet mass distribution is conducted, are shown with red boxes. The right plot is for the same decay sequence, with masses $ {m\, ( {\mathrm {G}_{\mathrm {KK}}} ) } = $ 5 TeV and $ {m\, ( \phi ) } = $ 1 TeV, for which the number of event categories is 9. For both plots, the cross-like shape is approximately centered on the second resonance pole mass ${m\, ( {\mathrm {R}_2} ) }$ for both the horizontal and the vertical axes. |
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Figure 3:
Distribution of the reconstructed mass of the ${\mathrm {R}_2}$ jet candidate vs. the reconstructed mass of the ${\mathrm {P}_3}$ jet candidate for events in data, which are expected to arise primarily from QCD multijet events. |
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Figure 4:
Dijet mass spectrum, from the combination of the spectra within 22 categories, from the search for a resonance with mass $ {m\, ( {\mathrm {R}_1} ) } = {m\, ( {\mathrm {G}_{\mathrm {KK}}} ) } = $ 2.9 TeV decaying to a second resonance with mass $ {m\, ( {\mathrm {R}_2} ) } = {m\, ( \phi ) } = $ 0.4 TeV and a gluon. The figure shows the data (black points), the resulting background-only fit (solid line) and its uncertainty (barely visible gray hatched area), and the signal normalized to a cross section equal to the 95% CL observed limit (dashed line). The data shown in each bin are the weighted sum of the number of events within each category, divided by the bin width, as a function of the dijet mass, with vertical bars representing the statistical uncertainty ($\sigma _{\text {stat}}$). The weights are the signal event fraction for each category, assuming a signal cross section equal to the 95% CL observed upper limit. The same quantities are also shown for the background-only fits in each category, and for the signal. The lower panel shows the difference between the data and the background prediction (points), and the background uncertainty (hatched gray area), divided by the statistical uncertainty. |
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Figure 5:
Observed upper limits on the product of signal cross section and branching fraction, as a function of ${\rho _{m}}$ vs. ${m\, ( {\mathrm {R}_1} ) }$, for a resonance model with three gluons in the final state. The excluded regions from this search (black hatched) are optimized for the $ {\mathrm {G}_{\mathrm {KK}}} \to \phi + \mathrm{g} \to \mathrm{g} \mathrm{g} \mathrm{g} $ decay with $ {g_{\text {grav}}} = $ 6.0 and $ {g_{\mathrm {GKK}}} = $ 3.0. These excluded regions are compared with those obtained from a reinterpretation of the inclusive CMS dijet resonance search (JHEP 05 (2020) 033, [2]), which is more sensitive to the decay channel $ {\mathrm {G}_{\mathrm {KK}}} \to \mathrm{q} \mathrm{\bar{q}} $ (red hatched). The vertical band between the ${m\, ( {\mathrm {R}_1} ) }$ values of $\approx $3.0 and $\approx $3.1 TeV, for $ {\rho _{m}} \lesssim $0.19, is not excluded by the dijet search because of an upward statistical fluctuation in the observed limit. The white, dashed lines represent a sample of curves corresponding to fixed ${m\, ( {\mathrm {R}_2} ) }$ values. |
| Summary |
| A search for high-mass hadronic resonances that decay to a parton and a Lorentz-boosted resonance, which in turn decays into a pair of partons, has been presented. This is the first dedicated search for resonances decaying into three final state partons at the LHC in events with a boosted resonance. No statistically significant excess above the background predictions is observed. Results are interpreted in a model with a warped extra dimension where the high-mass resonance is a Kaluza-Klein gluon, the boosted resonance is a radion, and the final-state partons are all gluons. By exploring a novel experimental signature, we significantly extend the excluded region in the parameter space of this benchmark model of new physics. In particular, the observed limits on the Kaluza-Klein gluon mass are extended by up to about 1 TeV compared to previous searches for dijet resonances. |
| Additional Figures | |
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Additional Figure 1:
In the simulation, reconstructed mass of the $\mathrm {R}_2$ jet candidate vs. the reconstructed mass of the $\mathrm {P}_3$ jet candidate (points) for $\mathrm {R}_1$ resonance events originating from a $\mathrm {G}_{\text {KK}}$ with a mass $m\, (\mathrm {G}_{\text {KK}} )=m\, (\mathrm {R}_1 ) = $ 7 TeV, decaying to a radion with a mass $m\, (\phi )=m\, (\mathrm {R}_2 ) = $ 1.4 TeV and a gluon. The event category in this plane, within which the search in the dijet mass distribution is conducted, is delimited by black lines. The cross-like shape is approximately centered on the second resonance pole mass $m\, (\mathrm {R}_2 )$ for both the horizontal and the vertical axes. |
png pdf |
Additional Figure 2:
Dijet mass spectrum, from the combination of the spectra within 22 categories, from the search for a resonance with mass $m\, (\mathrm {R}_1 ) = m\, (\mathrm {G}_{\text {KK}} ) = $ 2.9 TeV decaying to a second resonance with mass $m\, (\mathrm {R}_2 ) = m\, (\phi ) = $ 0.4 TeV and a gluon. This mass hypothesis corresponds to the largest excess observed, with a local significance of 3.2 standard deviations, and a global significance of 1.8 standard deviations. The figure shows the data (black points), the resulting background component of the signal+background fit (solid line) and its uncertainty (barely visible gray hatched area), and the signal normalized to the cross section resulting from the fit (dashed line). The data shown in each bin are the weighted sum of the number of events within each category, divided by the bin width, as a function of the dijet mass, with vertical bars representing the statistical uncertainty ($\sigma _{\text {stat}}$). The weights are the signal event fraction for each category, assuming a signal cross section equal to the 95% CL observed upper limit. The same quantities are also shown for the background and signal component of the fit. The lower panel shows the difference between the data and the background prediction (points), and the background uncertainty (hatched gray area), divided by the statistical uncertainty. |
png pdf |
Additional Figure 3:
Dijet mass spectrum, from the combination of the spectra within 22 categories, from the search for a resonance with mass $m\, (\mathrm {R}_1 ) = m\, (\mathrm {G}_{\text {KK}} ) = $ 4.2 TeV decaying to a second resonance with mass $m\, (\mathrm {R}_2 ) = m\, (\phi ) = $ 0.6 TeV and a gluon. This mass hypothesis corresponds to the second largest excess observed, with a local significance of 2.6 standard deviations, and a global significance below 1 standard deviation. The figure shows the data (black points), the resulting background-only fit (solid line) and its uncertainty (barely visible gray hatched area), and the signal normalized to a cross section equal to the 95% CL observed limit (dashed line). The data shown in each bin are the weighted sum of the number of events within each category, divided by the bin width, as a function of the dijet mass, with vertical bars representing the statistical uncertainty ($\sigma _{\text {stat}}$). The weights are the signal event fraction for each category, assuming a signal cross section equal to the 95% CL observed upper limit. The same quantities are also shown for the background-only fits in each category, and for the signal. The lower panel shows the difference between the data and the background prediction (points), and the background uncertainty (hatched gray area), divided by the statistical uncertainty. |
png pdf |
Additional Figure 4:
Dijet mass spectrum, from the combination of the spectra within 22 categories, from the search for a resonance with mass $m\, (\mathrm {R}_1 ) = m\, (\mathrm {G}_{\text {KK}} ) = $ 4.2 TeV decaying to a second resonance with mass $m\, (\mathrm {R}_2 ) = m\, (\phi ) = $ 0.6 TeV and a gluon. This mass hypothesis corresponds to the second largest excess observed, with a local significance of 2.6 standard deviations, and a global significance below 1 standard deviation. The figure shows the data (black points), the resulting background component of the signal+backgound fit (solid line) and its uncertainty (barely visible gray hatched area), and the signal normalized to the cross section resulting from the fit (dashed line). The data shown in each bin are the weighted sum of the number of events within each category, divided by the bin width, as a function of the dijet mass, with vertical bars representing the statistical uncertainty ($\sigma _{\text {stat}}$). The weights are the signal event fraction for each category, assuming a signal cross section equal to the 95% CL observed upper limit. The same quantities are also shown for the background and signal components of the fit. The lower panel shows the difference between the data and the background prediction (points), and the background uncertainty (hatched gray area), divided by the statistical uncertainty. |
png pdf |
Additional Figure 5:
Total signal efficiency for each signal hypothesis tested plotted as a function of the ratio between the masses of the two resonances $\rho _{m} = m\, (\mathrm {R}_2 )/m\, (\mathrm {R}_1 )$ and the mass of the first resonance $m\, (\mathrm {R}_1 )$. The total signal efficiency is defined as the total number of signal events that falls inside the event categories defined in the analysis, divided by the number of generated signal events. |
png pdf |
Additional Figure 6:
Expected 95% CL upper limits on signal cross section times branching fraction, as a function of the ratio $m\, (\mathrm {R}_2 )\, /\, m\, (\mathrm {R}_1 )$ vs. $m\, (\mathrm {R}_1 )$, for a trijet resonance model with 3 gluons in the final state. The limits are optimized for the decay of a Kaluza-Klein gluon ($\mathrm {G}_{\text {KK}}$) to a radion ($\phi $) and a gluon ($\mathrm {g}$) where the radion itself decays to 2 gluons, leading to a final state with 3 gluons ($\mathrm {ggg}$). The coupling parameters of the graviton and of the KK gluon (which are free paremeter of the theory) are respectively set to $g_{\text {grav}} = $ 6.0 and $g_{\mathrm {GKK}} = $ 3.0. |
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