CMS-PAS-EXO-22-016

CMS-PAS-EXO-22-016
Search for a high mass dimuon resonance associated with b quark jets at $\sqrt{s}=$ 13 TeV
CMS Collaboration
21 May 2023

Abstract: A search for high-mass dimuon resonance production in association with one or more b quark jets is presented. The study uses proton-proton collision data collected with the CMS detector at the LHC corresponding to an integrated luminosity of 138 fb $^{-1}$ at a center-of-mass energy of 13 TeV. Model-independent limits are derived on the number of events with b quark jets. Results are also interpreted in a lepton flavor-universal model with Z' boson couplings to a $\mathrm{bb}$ quark pair ( $g_{\mathrm{b}}$ ), an $\mathrm{sb}$ quark pair ( $g_{\mathrm{b}}\delta_{\mathrm{bs}}$ ), and any same-flavor charged lepton ( $g_{\ell}$ ) or neutrino pair ( $g_{\nu}$ ), with $g_{\nu}=g_{\ell}$ . For a Z' boson with a mass of 350 GeV (2 TeV) and $\delta_{\mathrm{bs}}\leq$ 0.25, the majority of the parameter space with 0.0057 $< g_{\ell} <$ 0.35 (0.25 $< g_{\ell} <$ 0.43) and 0.0079 $< g_{\mathrm{b}} <$ 0.46 (0.34 $< g_{\mathrm{b}} <$ 0.57) is excluded at 95% confidence level. Finally, constraints are set on a specific Z' model with parameters consistent with low-energy $\mathrm{b}\to\mathrm{s}\ell\ell$ measurements. In this scenario, most of the allowed parameter space is excluded for a Z' boson with a mass $\leq$ 500 GeV while the constraints are less stringent for higher Z' mass hypotheses.
Links: CDS record (PDF) ; Physics Briefing ; CADI line (restricted) ; These preliminary results are superseded in this paper, JHEP 10 (2023) 043. The superseded preliminary plots can be found here.

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Feynman diagrams of ${\mathrm{Z}^{'}} \to \mu^{+} \mu^{-}$ with a Z' produced via $\mathrm{b} \overline{\mathrm{b}} \to {\mathrm{Z}^{'}}$ or $\mathrm{s} \overline{\mathrm{b}} \to {\mathrm{Z}^{'}}$ , and at least one b quark in the final state. While a ${\mathrm{Z}^{'}} \mathrm{b}\mathrm{b}$ coupling may be present in any generic model, a ${\mathrm{Z}^{'}} \mathrm{s}\mathrm{b}$ coupling could arise through flavor mixing between second and third generation quarks.
png pdf	Figure 1-a: Feynman diagrams of ${\mathrm{Z}^{'}} \to \mu^{+} \mu^{-}$ with a Z' produced via $\mathrm{b} \overline{\mathrm{b}} \to {\mathrm{Z}^{'}}$ or $\mathrm{s} \overline{\mathrm{b}} \to {\mathrm{Z}^{'}}$ , and at least one b quark in the final state. While a ${\mathrm{Z}^{'}} \mathrm{b}\mathrm{b}$ coupling may be present in any generic model, a ${\mathrm{Z}^{'}} \mathrm{s}\mathrm{b}$ coupling could arise through flavor mixing between second and third generation quarks.
png pdf	Figure 1-b: Feynman diagrams of ${\mathrm{Z}^{'}} \to \mu^{+} \mu^{-}$ with a Z' produced via $\mathrm{b} \overline{\mathrm{b}} \to {\mathrm{Z}^{'}}$ or $\mathrm{s} \overline{\mathrm{b}} \to {\mathrm{Z}^{'}}$ , and at least one b quark in the final state. While a ${\mathrm{Z}^{'}} \mathrm{b}\mathrm{b}$ coupling may be present in any generic model, a ${\mathrm{Z}^{'}} \mathrm{s}\mathrm{b}$ coupling could arise through flavor mixing between second and third generation quarks.
png pdf	Figure 1-c: Feynman diagrams of ${\mathrm{Z}^{'}} \to \mu^{+} \mu^{-}$ with a Z' produced via $\mathrm{b} \overline{\mathrm{b}} \to {\mathrm{Z}^{'}}$ or $\mathrm{s} \overline{\mathrm{b}} \to {\mathrm{Z}^{'}}$ , and at least one b quark in the final state. While a ${\mathrm{Z}^{'}} \mathrm{b}\mathrm{b}$ coupling may be present in any generic model, a ${\mathrm{Z}^{'}} \mathrm{s}\mathrm{b}$ coupling could arise through flavor mixing between second and third generation quarks.
png pdf	Figure 1-d: Feynman diagrams of ${\mathrm{Z}^{'}} \to \mu^{+} \mu^{-}$ with a Z' produced via $\mathrm{b} \overline{\mathrm{b}} \to {\mathrm{Z}^{'}}$ or $\mathrm{s} \overline{\mathrm{b}} \to {\mathrm{Z}^{'}}$ , and at least one b quark in the final state. While a ${\mathrm{Z}^{'}} \mathrm{b}\mathrm{b}$ coupling may be present in any generic model, a ${\mathrm{Z}^{'}} \mathrm{s}\mathrm{b}$ coupling could arise through flavor mixing between second and third generation quarks.
png pdf	Figure 2: Distributions of $m_{\mu\mu}$ in the signal regions. The event categories $N_{\mathrm{b}}=$ 1 and $N_{\mathrm{b}}\geq$ 2 are shown on the left and right, respectively. The stacked histogram displays the expected distribution from the simulation of the SM backgrounds, while the overlaid open histograms illustrate the size and shape of the Z' contribution from the lepton flavor-universal model described in Eq. 1, for a variety of Z' mass hypotheses. For illustration purposes, we choose couplings $g_{\ell} = g_{\nu} = g_{\mathrm{b}} =$ 0.05 and $\delta_{\mathrm{b}\mathrm{s}}=$ 0. The observed data are shown as black points with statistical error bars. The SM background simulation is only used for illustration purposes, as the background is estimated directly from data across the full $m_{\mu\mu}$ range of interest.
png pdf	Figure 2-a: Distributions of $m_{\mu\mu}$ in the signal regions. The event categories $N_{\mathrm{b}}=$ 1 and $N_{\mathrm{b}}\geq$ 2 are shown on the left and right, respectively. The stacked histogram displays the expected distribution from the simulation of the SM backgrounds, while the overlaid open histograms illustrate the size and shape of the Z' contribution from the lepton flavor-universal model described in Eq. 1, for a variety of Z' mass hypotheses. For illustration purposes, we choose couplings $g_{\ell} = g_{\nu} = g_{\mathrm{b}} =$ 0.05 and $\delta_{\mathrm{b}\mathrm{s}}=$ 0. The observed data are shown as black points with statistical error bars. The SM background simulation is only used for illustration purposes, as the background is estimated directly from data across the full $m_{\mu\mu}$ range of interest.
png pdf	Figure 2-b: Distributions of $m_{\mu\mu}$ in the signal regions. The event categories $N_{\mathrm{b}}=$ 1 and $N_{\mathrm{b}}\geq$ 2 are shown on the left and right, respectively. The stacked histogram displays the expected distribution from the simulation of the SM backgrounds, while the overlaid open histograms illustrate the size and shape of the Z' contribution from the lepton flavor-universal model described in Eq. 1, for a variety of Z' mass hypotheses. For illustration purposes, we choose couplings $g_{\ell} = g_{\nu} = g_{\mathrm{b}} =$ 0.05 and $\delta_{\mathrm{b}\mathrm{s}}=$ 0. The observed data are shown as black points with statistical error bars. The SM background simulation is only used for illustration purposes, as the background is estimated directly from data across the full $m_{\mu\mu}$ range of interest.
png pdf	Figure 3: Invariant mass $m_{\mu\mu}$ distributions in the event categories with (left) $N_{\mathrm{b}}=$ 1 and (right) $N_{\mathrm{b}}\geq$ 2 shown together with the corresponding selected background functional forms used as input to the discrete profiling method [38] when probing the $m_{{\mathrm{Z}^{'}} }=$ 500 GeV hypothesis. For illustration purposes, we overlay the expected a signal distribution for the lepton flavor-universal model described in Eq. 1, with couplings $g_{\ell} = g_{\nu} = g_{\mathrm{b}} =$ 0.05 and $\delta_{\mathrm{b}\mathrm{s}}=$ 0. The signal distribution is scaled by a factor of 0.5 to improve visibility.
png pdf	Figure 3-a: Invariant mass $m_{\mu\mu}$ distributions in the event categories with (left) $N_{\mathrm{b}}=$ 1 and (right) $N_{\mathrm{b}}\geq$ 2 shown together with the corresponding selected background functional forms used as input to the discrete profiling method [38] when probing the $m_{{\mathrm{Z}^{'}} }=$ 500 GeV hypothesis. For illustration purposes, we overlay the expected a signal distribution for the lepton flavor-universal model described in Eq. 1, with couplings $g_{\ell} = g_{\nu} = g_{\mathrm{b}} =$ 0.05 and $\delta_{\mathrm{b}\mathrm{s}}=$ 0. The signal distribution is scaled by a factor of 0.5 to improve visibility.
png pdf	Figure 3-b: Invariant mass $m_{\mu\mu}$ distributions in the event categories with (left) $N_{\mathrm{b}}=$ 1 and (right) $N_{\mathrm{b}}\geq$ 2 shown together with the corresponding selected background functional forms used as input to the discrete profiling method [38] when probing the $m_{{\mathrm{Z}^{'}} }=$ 500 GeV hypothesis. For illustration purposes, we overlay the expected a signal distribution for the lepton flavor-universal model described in Eq. 1, with couplings $g_{\ell} = g_{\nu} = g_{\mathrm{b}} =$ 0.05 and $\delta_{\mathrm{b}\mathrm{s}}=$ 0. The signal distribution is scaled by a factor of 0.5 to improve visibility.
png pdf	Figure 4: Exclusion limits at 95% CL on the number of selected BSM events with $N_{\mathrm{b}} \geq$ 1 as a function of $m_{{\mathrm{Z}^{'}} }$ , for the different representative values of $f_{2\mathrm{b}}=$ 0 (top left), 0.5 (top right), and 1 (bottom). The quantity $f_{2\mathrm{b}}$ is the fraction of BSM events passing the analysis selection that have at least two b quark jets. The solid black (red) line represents the observed (median expected) exclusion. The inner green (outer yellow) band indicates the region containing 68 (95)% of the distribution of limits expected under the background-only hypothesis.
png pdf	Figure 4-a: Exclusion limits at 95% CL on the number of selected BSM events with $N_{\mathrm{b}} \geq$ 1 as a function of $m_{{\mathrm{Z}^{'}} }$ , for the different representative values of $f_{2\mathrm{b}}=$ 0 (top left), 0.5 (top right), and 1 (bottom). The quantity $f_{2\mathrm{b}}$ is the fraction of BSM events passing the analysis selection that have at least two b quark jets. The solid black (red) line represents the observed (median expected) exclusion. The inner green (outer yellow) band indicates the region containing 68 (95)% of the distribution of limits expected under the background-only hypothesis.
png pdf	Figure 4-b: Exclusion limits at 95% CL on the number of selected BSM events with $N_{\mathrm{b}} \geq$ 1 as a function of $m_{{\mathrm{Z}^{'}} }$ , for the different representative values of $f_{2\mathrm{b}}=$ 0 (top left), 0.5 (top right), and 1 (bottom). The quantity $f_{2\mathrm{b}}$ is the fraction of BSM events passing the analysis selection that have at least two b quark jets. The solid black (red) line represents the observed (median expected) exclusion. The inner green (outer yellow) band indicates the region containing 68 (95)% of the distribution of limits expected under the background-only hypothesis.
png pdf	Figure 4-c: Exclusion limits at 95% CL on the number of selected BSM events with $N_{\mathrm{b}} \geq$ 1 as a function of $m_{{\mathrm{Z}^{'}} }$ , for the different representative values of $f_{2\mathrm{b}}=$ 0 (top left), 0.5 (top right), and 1 (bottom). The quantity $f_{2\mathrm{b}}$ is the fraction of BSM events passing the analysis selection that have at least two b quark jets. The solid black (red) line represents the observed (median expected) exclusion. The inner green (outer yellow) band indicates the region containing 68 (95)% of the distribution of limits expected under the background-only hypothesis.
png pdf	Figure 5: Observed (solid) and median expected (dashed) exclusion limits at 95% CL in the $g_{\mathrm{b}}$ -- $g_{\ell}$ plane for the lepton flavor-universal model. The scenarios considered have $\delta_{\mathrm{b}\mathrm{s}}$ values of either 0 (left) or 0.25 (right). In all cases, we assume $g_{\nu} = g_{\ell}$ . The curves extend only up to coupling values at which the Z' width is equal to half of the $\mu\mu$ invariant mass resolution, marked by the dotted curves. Beyond these coupling values, the narrow width approximation intrinsic to the search strategy is not considered valid. The enclosed regions are excluded.
png pdf	Figure 5-a: Observed (solid) and median expected (dashed) exclusion limits at 95% CL in the $g_{\mathrm{b}}$ -- $g_{\ell}$ plane for the lepton flavor-universal model. The scenarios considered have $\delta_{\mathrm{b}\mathrm{s}}$ values of either 0 (left) or 0.25 (right). In all cases, we assume $g_{\nu} = g_{\ell}$ . The curves extend only up to coupling values at which the Z' width is equal to half of the $\mu\mu$ invariant mass resolution, marked by the dotted curves. Beyond these coupling values, the narrow width approximation intrinsic to the search strategy is not considered valid. The enclosed regions are excluded.
png pdf	Figure 5-b: Observed (solid) and median expected (dashed) exclusion limits at 95% CL in the $g_{\mathrm{b}}$ -- $g_{\ell}$ plane for the lepton flavor-universal model. The scenarios considered have $\delta_{\mathrm{b}\mathrm{s}}$ values of either 0 (left) or 0.25 (right). In all cases, we assume $g_{\nu} = g_{\ell}$ . The curves extend only up to coupling values at which the Z' width is equal to half of the $\mu\mu$ invariant mass resolution, marked by the dotted curves. Beyond these coupling values, the narrow width approximation intrinsic to the search strategy is not considered valid. The enclosed regions are excluded.
png pdf	Figure 6: Exclusion limits at 95% CL in the $\|\theta_{23}\|$ -- $g_{{\mathrm{Z}^{'}} }$ plane for the $B_3-L_2$ model [3], for representative values of $m_{{\mathrm{Z}^{'}} }$ . The solid (dashed) curves represent the observed (median expected) exclusions. The dotted lines denote the coupling values at which the Z' width equals one half of the $\mu\mu$ invariant mass resolution. Beyond these coupling values, the narrow width approximation intrinsic to the search strategy is not considered valid. For a given mass, the region enclosed between the solid (dashed) and the dotted lines is (expected to be) excluded. The dotted line for $m_{{\mathrm{Z}^{'}} } =$ 500 GeV lies beyond the displayed $g_{{\mathrm{Z}^{'}} }$ range and is, therefore, not shown. The shaded gray area represents the region preferred by the global fit from Ref. [3] at 95% CL, while the region above the green dash-dotted curve is incompatible at 95% CL with the measurement of the mass difference between the mass eigenstates of the neutral $\mathrm{B}_{s}$ mesons.

Tables

png pdf

Table 1:
Summary of signal uncertainties relevant in this analysis. The uncertainties are grouped based on whether they affect the normalization or the shape of the signal. The fit parameter

$\overline{m}_{\mu\mu}$ corresponds to the position of the maximum of the

$m_{\mu\mu}$ distribution after detector effects, and

$\overline{\sigma}_{\text{mass}}$ is the resolution parameter used in the fit, distinguished from the values of

$\sigma_{\text{mass}}$ extracted from simulation.

Summary

A search for high-mass dimuon resonance production in association with one or more b quark jets is presented, using data collected with the CMS experiment at the LHC that correspond to an integrated luminosity of 138 fb

$^{-1}$ at a center-of-mass energy of 13 TeV. Model-independent limits are derived on the total number of signal events with

$N_{\mathrm{b}}=$ 1 and

$\geq$ 2, varying the relative fraction of events with

$N_{\mathrm{b}}\geq$ 2. The limits are presented as a function of the analyzed dimuon resonance mass values. Results are also interpreted in terms of a lepton flavor-universal model that involves Z' boson couplings to b quarks (

$g_{\mathrm{b}}$ ) and muons, where the Z' boson couplings to all neutrinos (

$g_{\nu}$ ) and to all charged leptons (

$g_{\ell}$ ) are assumed to be equal, the

$g_{\mathrm{b}}$ coupling scales both

${\mathrm{Z}^{'}} \mathrm{b}\mathrm{b}$ and

${\mathrm{Z}^{'}} \mathrm{s}\mathrm{b}$ interactions, and a separate

$\delta_{\mathrm{b}\mathrm{s}}$ coupling solely scales the

${\mathrm{Z}^{'}} \mathrm{s}\mathrm{b}$ interaction. The exclusions in this model are presented in terms of the coupling strengths

$g_{\ell}$ and

$g_{\mathrm{b}}$ , and

$m_{{\mathrm{Z}^{'}} }$ . For a Z' boson with a mass of 350 GeV (2 TeV) and

$\delta_{\mathrm{b}\mathrm{s}}\leq$ 0.25, the majority of the parameter space with 0.0057

$< g_{\ell} <$ 0.35 (0.25

$< g_{\ell} <$ 0.43) and 0.0079

$< g_{\mathrm{b}} <$ 0.46 (0.34

$< g_{\mathrm{b}} <$ 0.57) is excluded at 95% confidence level. Finally, constraints are set on a model where the production of a Z' boson is predicted to have implications in low-energy

$\mathrm{b}\to\mathrm{s}\ell\ell$ observables. In this scenario, most of the allowed parameter space is excluded for a Z' boson with a mass

$\leq$ 500 GeV while the constraints are less stringent for higher Z' mass hypotheses.

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