CMS-PAS-EXO-24-007

CMS-PAS-EXO-24-007
Search for low mass vector and scalar resonances decaying into quark-antiquark pairs
CMS Collaboration
19 July 2024

Abstract: A search for low mass resonances decaying into quark-antiquark pairs is presented. The analysis uses proton-proton collision data at $ \sqrt{s}= $ 13 TeV collected by the CMS detector at the CERN LHC, corresponding to an integrated luminosity of 138 fb$ ^{-1} $. The search targets resonances with masses from 50 to 300 GeV, produced in association with large initial-state radiation. Two coupling scenarios are considered, with the resonances coupling either equally to all flavors of quark or preferentially to bottom quarks. The resonances are reconstructed as large-radius jets with two-pronged substructure and are identified using the ParticleNet algorithm. Separate signal regions are defined to target resonances decaying to light- or heavy-flavor quarks. The invariant jet mass spectrum is scrutinized for narrow excesses over a smoothly falling background. No evidence for such resonances is observed, and limits are set on the couplings of new scalar and vector resonances to quarks. For dijet resonances with masses from 50-300 GeV, these are the most sensitive limits to date.
Links: CDS record (PDF) ; Physics Briefing ; CADI line (restricted) ;

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Representative $ m_{\rm SD} $ distributions for the $ \mathrm{W}(\mathrm{q}\overline{\mathrm{q}}') $ control region, for events passing (left) and failing (right) the $ p_{\textrm{2-prong}} $ requirement. The data and fitted templates are shown for the 2018 data-taking period. The matched component (orange) corresponds to jets matched to boosted W bosons from $ \mathrm{t}\overline{\mathrm{t}} $ events, while the unmatched component (blue) comprises nonresonant backgrounds.
png pdf	Figure 1-a: Representative $ m_{\rm SD} $ distributions for the $ \mathrm{W}(\mathrm{q}\overline{\mathrm{q}}') $ control region, for events passing (left) and failing (right) the $ p_{\textrm{2-prong}} $ requirement. The data and fitted templates are shown for the 2018 data-taking period. The matched component (orange) corresponds to jets matched to boosted W bosons from $ \mathrm{t}\overline{\mathrm{t}} $ events, while the unmatched component (blue) comprises nonresonant backgrounds.
png pdf	Figure 1-b: Representative $ m_{\rm SD} $ distributions for the $ \mathrm{W}(\mathrm{q}\overline{\mathrm{q}}') $ control region, for events passing (left) and failing (right) the $ p_{\textrm{2-prong}} $ requirement. The data and fitted templates are shown for the 2018 data-taking period. The matched component (orange) corresponds to jets matched to boosted W bosons from $ \mathrm{t}\overline{\mathrm{t}} $ events, while the unmatched component (blue) comprises nonresonant backgrounds.
png pdf	Figure 2: The jet $ m_{\rm SD} $ distributions in the high-$ p_{\textrm{bvl}} $ (left) and low-$ p_{\textrm{bvl}} $ (right) signal regions, fitted with a signal-plus-background hypothesis corresponding to a Z' boson with a mass of $ m(\mathrm{Z}')= $ 220 GeV. The distributions are summed across all five $ p_{\mathrm{T}} $ bins and the four data-taking periods. The dashed lines represent the expected Z' signal yields for $ g_{\mathrm{q}}= $ 0.25 multiplied by a factor of two for visibility, while the fitted signal itself is shown as a hatched area. The lower panel shows the residual difference between the data and the overall background, divided by the statistical uncertainty in the data.
png pdf	Figure 2-a: The jet $ m_{\rm SD} $ distributions in the high-$ p_{\textrm{bvl}} $ (left) and low-$ p_{\textrm{bvl}} $ (right) signal regions, fitted with a signal-plus-background hypothesis corresponding to a Z' boson with a mass of $ m(\mathrm{Z}')= $ 220 GeV. The distributions are summed across all five $ p_{\mathrm{T}} $ bins and the four data-taking periods. The dashed lines represent the expected Z' signal yields for $ g_{\mathrm{q}}= $ 0.25 multiplied by a factor of two for visibility, while the fitted signal itself is shown as a hatched area. The lower panel shows the residual difference between the data and the overall background, divided by the statistical uncertainty in the data.
png pdf	Figure 2-b: The jet $ m_{\rm SD} $ distributions in the high-$ p_{\textrm{bvl}} $ (left) and low-$ p_{\textrm{bvl}} $ (right) signal regions, fitted with a signal-plus-background hypothesis corresponding to a Z' boson with a mass of $ m(\mathrm{Z}')= $ 220 GeV. The distributions are summed across all five $ p_{\mathrm{T}} $ bins and the four data-taking periods. The dashed lines represent the expected Z' signal yields for $ g_{\mathrm{q}}= $ 0.25 multiplied by a factor of two for visibility, while the fitted signal itself is shown as a hatched area. The lower panel shows the residual difference between the data and the overall background, divided by the statistical uncertainty in the data.
png pdf	Figure 3: Upper limits at 95% CL on the coupling $ g_{\mathrm{q}} $ between the Z' boson and quarks. The Z' boson is assumed to couple equally to quarks of all flavors, and to decay to quark-antiquark pairs with 100% branching fraction. The solid line represents the observed limits, while the dashed line and the green and yellow bands represent the expected limits and its variation at the one and two standard deviation levels.
png pdf	Figure 4: Upper limits at 95% CL on the coupling parameters $ g_{\mathrm{q}\phi} $ (left) and $ g_{\mathrm{q}\mathrm{A}} $ (right). The $ \phi $ or A bosons couple to quarks with a coupling given by $ g_{\mathrm{q}\phi} $ or $ g_{\mathrm{q}\mathrm{A}} $ times the SM Yukawa couplings, respectively, and decay dominantly to bottom quark-antiquark pairs. The solid line represents the observed limits, while the dashed line and the green and yellow bands represent the expected limits and its variation at the one and two standard deviation levels.
png pdf	Figure 4-a: Upper limits at 95% CL on the coupling parameters $ g_{\mathrm{q}\phi} $ (left) and $ g_{\mathrm{q}\mathrm{A}} $ (right). The $ \phi $ or A bosons couple to quarks with a coupling given by $ g_{\mathrm{q}\phi} $ or $ g_{\mathrm{q}\mathrm{A}} $ times the SM Yukawa couplings, respectively, and decay dominantly to bottom quark-antiquark pairs. The solid line represents the observed limits, while the dashed line and the green and yellow bands represent the expected limits and its variation at the one and two standard deviation levels.
png pdf	Figure 4-b: Upper limits at 95% CL on the coupling parameters $ g_{\mathrm{q}\phi} $ (left) and $ g_{\mathrm{q}\mathrm{A}} $ (right). The $ \phi $ or A bosons couple to quarks with a coupling given by $ g_{\mathrm{q}\phi} $ or $ g_{\mathrm{q}\mathrm{A}} $ times the SM Yukawa couplings, respectively, and decay dominantly to bottom quark-antiquark pairs. The solid line represents the observed limits, while the dashed line and the green and yellow bands represent the expected limits and its variation at the one and two standard deviation levels.

Tables
png pdf	Table 1: Summary of scale factors extracted from the $ \mathrm{W}(\mathrm{q}\overline{\mathrm{q}}') $ control region. The $ f_{\textrm{2-prong}} $ parameter corrects the efficiency of the 2-prong tagger requirement, $ \delta_m $ corrects the $ m_{\rm SD} $ scale, and $ \delta_{\sigma} $ corrects the $ m_{\rm SD} $ resolution. Separate scale factors are derived for each data-taking period.
png pdf	Table 2: Summary of transfer factor orders $ TF_{MC} $ and $ TF_{res} $ in order ($ p_{\mathrm{T}} $, $ \rho $) per year. $ TF_{MC} $ is derived with QCD MC dataset, while $ TF_{res} $ is derived with data.

Summary

A search for new dijet resonances with masses from 50-300 GeV has been presented. The search targets spin-1 resonances decaying equally to quark-antiquark pairs of all flavors and spin-0 resonances decaying to bottom quark-antiquark pairs. To circumvent trigger bandwidth limitations, the resonances are required to be produced with significant initial state radiation, and, thus, have large transverse momentum. Because of the large transverse momentum, the resonances are reconstructed as single large-radius jets with 2-pronged substructure. The resonances are distinguished from the backgrounds using the ParticleNet algorithm and identified as narrow peaks in the jet soft-drop mass spectra. No significant excesses above the standard model expectations are observed, and limits are set on the couplings of the resonances to quarks, assuming that the resonances decay only to quarks. For spin-1 resonances coupling equally to all quark flavors, the upper limits on $ g_{\mathrm{q}} $ range from 0.04-0.15. For spin-0 resonances coupling dominantly to bottom quarks, the upper limits on $ g_{\mathrm{q}\phi} $ ($ g_{\mathrm{q}\mathrm{A}} $) range from 1.5-5.8 (1.0-3.8). These are the most sensitive limits to date on dijet resonances with masses from 50-300 GeV.

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