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| CMS-PAS-EXO-22-006 | ||
| Search for lepton flavour universality violation via production of a new neutral gauge boson decaying to two muons with one or two b-jets in pp collisions at $ \sqrt{s}= $ 13 TeV | ||
| CMS Collaboration | ||
| 19 July 2024 | ||
| Abstract: A search is presented for a new neutral boson, Z', produced in association with one or two jets, including at least one b jet, and decaying into two muons. Current exclusion bounds on this signature are looser than those for Z' produced via light quark fusion. The analysis is performed using data collected in 2016--2018 with the CMS detector in proton-proton collisions at $ \sqrt{s}= $ 13 TeV and corresponding to an integrated luminosity of 138 fb$ ^{-1} $. No significant deviation from background expectations is observed. Limits at 95% CL on the product of cross section, branching fraction, and acceptance are set, ranging from 0.2 to 2 fb, for Z' masses between 127 and 352 GeV. Model-independent upper limits on signal yield and generator-process-dependent acceptances are provided. | ||
| Links: CDS record (PDF) ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Representative Feynman diagrams of Z' production via bottom-bottom or bottom-strange quark fusion and decaying in a dimuon final state. Tree-level production (left), single associated initial state radiation (ISR) jet production (middle), and two associated ISR jet production (right) are shown. |
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Figure 1-a:
Representative Feynman diagrams of Z' production via bottom-bottom or bottom-strange quark fusion and decaying in a dimuon final state. Tree-level production (left), single associated initial state radiation (ISR) jet production (middle), and two associated ISR jet production (right) are shown. |
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Figure 1-b:
Representative Feynman diagrams of Z' production via bottom-bottom or bottom-strange quark fusion and decaying in a dimuon final state. Tree-level production (left), single associated initial state radiation (ISR) jet production (middle), and two associated ISR jet production (right) are shown. |
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Figure 1-c:
Representative Feynman diagrams of Z' production via bottom-bottom or bottom-strange quark fusion and decaying in a dimuon final state. Tree-level production (left), single associated initial state radiation (ISR) jet production (middle), and two associated ISR jet production (right) are shown. |
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Figure 2:
Histograms for search-specific variables after object selections including a single muon requirement and categorization into both jet multiplicities in Run 2 simulation. $ H_{\textrm{T}}-L_{\textrm{T}} $ distributions are on the left, $ p_{\mathrm{T}}^\text{miss} /m_{\ell\ell} $ distributions on the right. 1-jet category distributions are on top, 2-jet category distributions on the bottom. |
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Figure 2-a:
Histograms for search-specific variables after object selections including a single muon requirement and categorization into both jet multiplicities in Run 2 simulation. $ H_{\textrm{T}}-L_{\textrm{T}} $ distributions are on the left, $ p_{\mathrm{T}}^\text{miss} /m_{\ell\ell} $ distributions on the right. 1-jet category distributions are on top, 2-jet category distributions on the bottom. |
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Figure 2-b:
Histograms for search-specific variables after object selections including a single muon requirement and categorization into both jet multiplicities in Run 2 simulation. $ H_{\textrm{T}}-L_{\textrm{T}} $ distributions are on the left, $ p_{\mathrm{T}}^\text{miss} /m_{\ell\ell} $ distributions on the right. 1-jet category distributions are on top, 2-jet category distributions on the bottom. |
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Figure 2-c:
Histograms for search-specific variables after object selections including a single muon requirement and categorization into both jet multiplicities in Run 2 simulation. $ H_{\textrm{T}}-L_{\textrm{T}} $ distributions are on the left, $ p_{\mathrm{T}}^\text{miss} /m_{\ell\ell} $ distributions on the right. 1-jet category distributions are on top, 2-jet category distributions on the bottom. |
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Figure 2-d:
Histograms for search-specific variables after object selections including a single muon requirement and categorization into both jet multiplicities in Run 2 simulation. $ H_{\textrm{T}}-L_{\textrm{T}} $ distributions are on the left, $ p_{\mathrm{T}}^\text{miss} /m_{\ell\ell} $ distributions on the right. 1-jet category distributions are on top, 2-jet category distributions on the bottom. |
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Figure 3:
A visual demonstration of the ABCD control regions and signal regions. For example, 'A' represents our dimuon, b-enriched signal regions ($ SR_b^{\mu\mu} $ or $ SR_{b+j/b}^{\mu\mu} $), 'B' represents our b-enriched, dielectron control regions ($ CR_b^{ee} $ or $ CR_{b+j/b}^{ee} $), and so forth. |
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Figure 4:
Comparison between MC distribution in the signal region and background prediction from the ABCD method applied to MC control regions. Left: $ SR_b^{\mu\mu} $. Right: $ SR_{b+j/b}^{\mu\mu} $. |
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Figure 4-a:
Comparison between MC distribution in the signal region and background prediction from the ABCD method applied to MC control regions. Left: $ SR_b^{\mu\mu} $. Right: $ SR_{b+j/b}^{\mu\mu} $. |
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Figure 4-b:
Comparison between MC distribution in the signal region and background prediction from the ABCD method applied to MC control regions. Left: $ SR_b^{\mu\mu} $. Right: $ SR_{b+j/b}^{\mu\mu} $. |
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Figure 5:
1-jet control regions with data fits used for the $ SR_b^{\mu\mu} $ background prediction. Left: $ CR_j^{\mu\mu} $. Middle: $ CR_b^{ee} $. Right: $ CR_j^{ee} $. |
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Figure 5-a:
1-jet control regions with data fits used for the $ SR_b^{\mu\mu} $ background prediction. Left: $ CR_j^{\mu\mu} $. Middle: $ CR_b^{ee} $. Right: $ CR_j^{ee} $. |
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Figure 5-b:
1-jet control regions with data fits used for the $ SR_b^{\mu\mu} $ background prediction. Left: $ CR_j^{\mu\mu} $. Middle: $ CR_b^{ee} $. Right: $ CR_j^{ee} $. |
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Figure 5-c:
1-jet control regions with data fits used for the $ SR_b^{\mu\mu} $ background prediction. Left: $ CR_j^{\mu\mu} $. Middle: $ CR_b^{ee} $. Right: $ CR_j^{ee} $. |
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Figure 6:
2-jet control regions with data fits used for the $ SR_{b+j/b}^{\mu\mu} $ background prediction. Left: $ CR_{2j}^{\mu\mu} $. Middle: $ CR_{b+j/b}^{ee} $. Right: $ CR_{2j}^{ee} $. |
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Figure 6-a:
2-jet control regions with data fits used for the $ SR_{b+j/b}^{\mu\mu} $ background prediction. Left: $ CR_{2j}^{\mu\mu} $. Middle: $ CR_{b+j/b}^{ee} $. Right: $ CR_{2j}^{ee} $. |
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Figure 6-b:
2-jet control regions with data fits used for the $ SR_{b+j/b}^{\mu\mu} $ background prediction. Left: $ CR_{2j}^{\mu\mu} $. Middle: $ CR_{b+j/b}^{ee} $. Right: $ CR_{2j}^{ee} $. |
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Figure 6-c:
2-jet control regions with data fits used for the $ SR_{b+j/b}^{\mu\mu} $ background prediction. Left: $ CR_{2j}^{\mu\mu} $. Middle: $ CR_{b+j/b}^{ee} $. Right: $ CR_{2j}^{ee} $. |
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Figure 7:
Distributions of $ m_{\ell\ell} $ in the $ SR_b^{\mu\mu} $ (left) and $ SR_{b+j/b}^{\mu\mu} $ (right) signal regions. Simulated signal shapes at 125, 250 and 350 GeV are shown. |
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Figure 7-a:
Distributions of $ m_{\ell\ell} $ in the $ SR_b^{\mu\mu} $ (left) and $ SR_{b+j/b}^{\mu\mu} $ (right) signal regions. Simulated signal shapes at 125, 250 and 350 GeV are shown. |
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Figure 7-b:
Distributions of $ m_{\ell\ell} $ in the $ SR_b^{\mu\mu} $ (left) and $ SR_{b+j/b}^{\mu\mu} $ (right) signal regions. Simulated signal shapes at 125, 250 and 350 GeV are shown. |
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Figure 8:
Data (black) vs ABCD prediction (red) for 2016 (left), 2017 (middle), and 2018 (right) in $ SR_b^{\mu\mu} $. The gray band shows the propagated uncertainty of all individual fit variations in a given bin, which we consider to be uncorrelated. The red error bars indicate the ABCD fit uncertainty. |
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Figure 8-a:
Data (black) vs ABCD prediction (red) for 2016 (left), 2017 (middle), and 2018 (right) in $ SR_b^{\mu\mu} $. The gray band shows the propagated uncertainty of all individual fit variations in a given bin, which we consider to be uncorrelated. The red error bars indicate the ABCD fit uncertainty. |
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Figure 8-b:
Data (black) vs ABCD prediction (red) for 2016 (left), 2017 (middle), and 2018 (right) in $ SR_b^{\mu\mu} $. The gray band shows the propagated uncertainty of all individual fit variations in a given bin, which we consider to be uncorrelated. The red error bars indicate the ABCD fit uncertainty. |
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Figure 8-c:
Data (black) vs ABCD prediction (red) for 2016 (left), 2017 (middle), and 2018 (right) in $ SR_b^{\mu\mu} $. The gray band shows the propagated uncertainty of all individual fit variations in a given bin, which we consider to be uncorrelated. The red error bars indicate the ABCD fit uncertainty. |
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Figure 9:
Data (black) vs ABCD prediction (red) for 2016 (left), 2017 (middle), and 2018 (right) in $ SR_{b+j/b}^{\mu\mu} $. The gray band shows the propagated uncertainty of all individual fit variations in a given bin, which we consider to be uncorrelated. The red error bars indicate the ABCD fit uncertainty. |
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Figure 9-a:
Data (black) vs ABCD prediction (red) for 2016 (left), 2017 (middle), and 2018 (right) in $ SR_{b+j/b}^{\mu\mu} $. The gray band shows the propagated uncertainty of all individual fit variations in a given bin, which we consider to be uncorrelated. The red error bars indicate the ABCD fit uncertainty. |
png pdf |
Figure 9-b:
Data (black) vs ABCD prediction (red) for 2016 (left), 2017 (middle), and 2018 (right) in $ SR_{b+j/b}^{\mu\mu} $. The gray band shows the propagated uncertainty of all individual fit variations in a given bin, which we consider to be uncorrelated. The red error bars indicate the ABCD fit uncertainty. |
png pdf |
Figure 9-c:
Data (black) vs ABCD prediction (red) for 2016 (left), 2017 (middle), and 2018 (right) in $ SR_{b+j/b}^{\mu\mu} $. The gray band shows the propagated uncertainty of all individual fit variations in a given bin, which we consider to be uncorrelated. The red error bars indicate the ABCD fit uncertainty. |
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Figure 10:
95% confidence level limits on acceptance times cross section times branching fraction to dimuon decays. Left is $ SR_b^{\mu\mu} $, right is $ SR_{b+j/b}^{\mu\mu} $. A combination of both limits depends on the relative acceptance contributions in each region and is omitted here. |
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Figure 10-a:
95% confidence level limits on acceptance times cross section times branching fraction to dimuon decays. Left is $ SR_b^{\mu\mu} $, right is $ SR_{b+j/b}^{\mu\mu} $. A combination of both limits depends on the relative acceptance contributions in each region and is omitted here. |
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Figure 10-b:
95% confidence level limits on acceptance times cross section times branching fraction to dimuon decays. Left is $ SR_b^{\mu\mu} $, right is $ SR_{b+j/b}^{\mu\mu} $. A combination of both limits depends on the relative acceptance contributions in each region and is omitted here. |
| Tables | |
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Table 1:
Summary of object selection requirements on leptons, veto leptons, and jets passing and failing b-jet identification. The efficiencies of the respective identification working points are detailed in the text of Section 2. |
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Table 2:
Signal and control regions based on opposite sign dilepton pair flavour and jet multiplicity, b-tagged ($ N_{\textrm{b}} $) and total ($ N^{\textrm{all}}_{\textrm{jets}} $). Events with more than two leptons passing veto lepton selections of any flavour are discarded. Note that the signal model Z' does not decay into electrons, hence the use of dielectron control regions. |
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Table 3:
Summary of additional $ m_{\ell\ell} $-dependent event selection requirements on $ p_{\mathrm{T}}^\text{miss} $ and $ H_{\textrm{T}}-L_{\textrm{T}} $ to suppress backgrounds. |
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Table 4:
Overview of systematic uncertainty sources and their range of variation. Components of the final fit these uncertainties relate to and partial correlations across years are also indicated by a "corr." in their uncertainty source description. |
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Table 5:
Acceptances by signal region for events with no ME generator-level ISR jets of strange or bottom flavour. Exactly one bottom quark contributes directly to the Z' production vertex. Statistical and systematic uncertainties for this 0b(1b) category are listed. |
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Table 6:
Acceptances by signal region for events with no ME generator-level ISR jets of strange or bottom flavour. Exactly two bottom quarks contribute directly to the Z' production vertex. Statistical and systematic uncertainties for this 0b(2b) category are listed. |
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Table 7:
Acceptances by signal region for events with exactly one ME generator-level ISR jet of bottom flavour. Statistical and systematic uncertainties for this 1b category are listed. |
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Table 8:
Acceptances by signal region for events with exactly one ME generator-level ISR jet of strange flavour. Statistical and systematic uncertainties for this 1s category are listed. |
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Table 9:
Acceptances by signal region for events with exactly two ME generator-level ISR jets, one of which has strange, the other bottom flavour. Statistical and systematic uncertainties for this 1b+1s category are listed. |
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Table 10:
Acceptances by signal region for events with exactly two ME generator-level ISR jets of bottom flavour. Statistical and systematic uncertainties for this 2b category are listed. |
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Table 11:
Acceptances by signal region for events with exactly two ME generator-level ISR jets of strange flavour. Statistical and systematic uncertainties for this 2s category are listed. |
| Summary |
| A search for lepton flavour universality violation by a new neutral gauge boson decaying to two muons with one or two associated jets, out of which at least one is b-tagged, has been presented. The basis for the analysis is LHC proton-proton collision data collected by the CMS experiment from 2016--2018, corresponding to an integrated luminosity of 137.58 fb$ ^{-1} $. Data are consistent with background only, with no evidence of a signal. The limits obtained are the only ones for $ \sqrt{\mathrm{s}}= $ 13 TeV for masses between 126.7 and 351.8 GeV, and they are the most stringent for masses between 200 and 351.8 GeV. The data have been presented in a model-independent way, with acceptances reported by production category as a function of Z' mass, to cover any mixture of b- and s-quark production of that possible Z'. |
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Compact Muon Solenoid LHC, CERN |
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