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| CMS-PAS-HIG-21-013 | ||
| Evidence for off-shell Higgs boson production and first measurement of its width | ||
| CMS Collaboration | ||
| October 2021 | ||
| Abstract: The first measurement of the Higgs boson (H) width is performed based on evidence for off-shell H production in the final state with two Z bosons decaying into either four charged leptons (e or $\mu$), or two charged leptons and two neutrinos. Results are based on data from the CMS experiment at the LHC at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of up to 140 fb$^{-1}$. The total size of off-shell H production beyond the Z boson pair production threshold is constrained at 95% confidence to be within the interval [0.0061, 2.0] times its standard model (SM) expectation. The scenario with no off-shell production is excluded at a confidence level larger than 99.9% (3.6 standard deviations). The width of the H boson is then extracted to be $\Gamma_{\mathrm{H}} = $ 3.2$_{-1.7}^{+2.4}$ MeV, in agreement with the SM expectation of 4.1 MeV. The data are also used to set new constraints on anomalous H boson couplings to massive electroweak vector boson pairs. | ||
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Links:
CDS record (PDF) ;
Physics Briefing ;
CADI line (restricted) ;
These preliminary results are superseded in this paper, NP 18 (2022) 1329. The superseded preliminary plots can be found here. |
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| Figures | |
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Figure 1:
Observed (solid) and expected (dashed) likelihood scans for $ {\mu ^{\mathrm {off-shell}}_{{\mathrm {F}} {}}} $ or $ {\mu ^{\mathrm {off-shell}}_{{\mathrm {V}} {}}} $ (left), $ {\mu ^{\mathrm {off-shell}}} $ (middle), and ${\Gamma _{\mathrm{H} {}}}$ (right). Scans for $ {\mu ^{\mathrm {off-shell}}_{{\mathrm {F}} {}}} $ (blue) and $ {\mu ^{\mathrm {off-shell}}_{{\mathrm {V}} {}}} $ (magenta) are obtained with the other parameter unconstrained. Those for $ {\mu ^{\mathrm {off-shell}}} $ are shown with (blue) and without (magenta) the constraint $ {R^{\mathrm {off-shell}}_{{\mathrm {V}} {}, {\mathrm {F}} {}}} =$ 1. Constraints on ${\Gamma _{\mathrm{H} {}}}$ are shown with and without anomalous HVV couplings. The horizontal lines indicate the 68% and 95% CL regions. |
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Figure 1-a:
Observed (solid) and expected (dashed) likelihood scans for $ {\mu ^{\mathrm {off-shell}}_{{\mathrm {F}} {}}} $ or $ {\mu ^{\mathrm {off-shell}}_{{\mathrm {V}} {}}} $ (left), $ {\mu ^{\mathrm {off-shell}}} $ (middle), and ${\Gamma _{\mathrm{H} {}}}$ (right). Scans for $ {\mu ^{\mathrm {off-shell}}_{{\mathrm {F}} {}}} $ (blue) and $ {\mu ^{\mathrm {off-shell}}_{{\mathrm {V}} {}}} $ (magenta) are obtained with the other parameter unconstrained. Those for $ {\mu ^{\mathrm {off-shell}}} $ are shown with (blue) and without (magenta) the constraint $ {R^{\mathrm {off-shell}}_{{\mathrm {V}} {}, {\mathrm {F}} {}}} =$ 1. Constraints on ${\Gamma _{\mathrm{H} {}}}$ are shown with and without anomalous HVV couplings. The horizontal lines indicate the 68% and 95% CL regions. |
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Figure 1-b:
Observed (solid) and expected (dashed) likelihood scans for $ {\mu ^{\mathrm {off-shell}}_{{\mathrm {F}} {}}} $ or $ {\mu ^{\mathrm {off-shell}}_{{\mathrm {V}} {}}} $ (left), $ {\mu ^{\mathrm {off-shell}}} $ (middle), and ${\Gamma _{\mathrm{H} {}}}$ (right). Scans for $ {\mu ^{\mathrm {off-shell}}_{{\mathrm {F}} {}}} $ (blue) and $ {\mu ^{\mathrm {off-shell}}_{{\mathrm {V}} {}}} $ (magenta) are obtained with the other parameter unconstrained. Those for $ {\mu ^{\mathrm {off-shell}}} $ are shown with (blue) and without (magenta) the constraint $ {R^{\mathrm {off-shell}}_{{\mathrm {V}} {}, {\mathrm {F}} {}}} =$ 1. Constraints on ${\Gamma _{\mathrm{H} {}}}$ are shown with and without anomalous HVV couplings. The horizontal lines indicate the 68% and 95% CL regions. |
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Figure 1-c:
Observed (solid) and expected (dashed) likelihood scans for $ {\mu ^{\mathrm {off-shell}}_{{\mathrm {F}} {}}} $ or $ {\mu ^{\mathrm {off-shell}}_{{\mathrm {V}} {}}} $ (left), $ {\mu ^{\mathrm {off-shell}}} $ (middle), and ${\Gamma _{\mathrm{H} {}}}$ (right). Scans for $ {\mu ^{\mathrm {off-shell}}_{{\mathrm {F}} {}}} $ (blue) and $ {\mu ^{\mathrm {off-shell}}_{{\mathrm {V}} {}}} $ (magenta) are obtained with the other parameter unconstrained. Those for $ {\mu ^{\mathrm {off-shell}}} $ are shown with (blue) and without (magenta) the constraint $ {R^{\mathrm {off-shell}}_{{\mathrm {V}} {}, {\mathrm {F}} {}}} =$ 1. Constraints on ${\Gamma _{\mathrm{H} {}}}$ are shown with and without anomalous HVV couplings. The horizontal lines indicate the 68% and 95% CL regions. |
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Figure 2:
Two-parameter likelihood scan of $ {\mu ^{\mathrm {off-shell}}_{{\mathrm {F}} {}}} $ and $ {\mu ^{\mathrm {off-shell}}_{{\mathrm {V}} {}}} $. The dot-dashed and dashed contours enclose the 68% and 95% CL regions. The cross marks the minimum, and the blue rhombus marks the SM expectation. |
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Figure 3:
Likelihood scans of ${{f_{a 2}}}$ (left), ${{f_{a 3}}}$ (middle), and ${{f_{{\lambda}bda 1}}}$ (right) are shown with the constraint $ {\Gamma _{\mathrm{H} {}}} = {\Gamma _{\mathrm{H} {}}^{\mathrm {SM}}} $ (blue), ${\Gamma _{\mathrm{H} {}}}$ unconstrained (violet), or based on on-shell 4$\ell $ only (green). Observed (expected) scans are shown with solid (dashed) curves. The horizontal lines indicate the 68% and 95% CL regions. |
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Figure 3-a:
Likelihood scans of ${{f_{a 2}}}$ (left), ${{f_{a 3}}}$ (middle), and ${{f_{{\lambda}bda 1}}}$ (right) are shown with the constraint $ {\Gamma _{\mathrm{H} {}}} = {\Gamma _{\mathrm{H} {}}^{\mathrm {SM}}} $ (blue), ${\Gamma _{\mathrm{H} {}}}$ unconstrained (violet), or based on on-shell 4$\ell $ only (green). Observed (expected) scans are shown with solid (dashed) curves. The horizontal lines indicate the 68% and 95% CL regions. |
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Figure 3-b:
Likelihood scans of ${{f_{a 2}}}$ (left), ${{f_{a 3}}}$ (middle), and ${{f_{{\lambda}bda 1}}}$ (right) are shown with the constraint $ {\Gamma _{\mathrm{H} {}}} = {\Gamma _{\mathrm{H} {}}^{\mathrm {SM}}} $ (blue), ${\Gamma _{\mathrm{H} {}}}$ unconstrained (violet), or based on on-shell 4$\ell $ only (green). Observed (expected) scans are shown with solid (dashed) curves. The horizontal lines indicate the 68% and 95% CL regions. |
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Figure 3-c:
Likelihood scans of ${{f_{a 2}}}$ (left), ${{f_{a 3}}}$ (middle), and ${{f_{{\lambda}bda 1}}}$ (right) are shown with the constraint $ {\Gamma _{\mathrm{H} {}}} = {\Gamma _{\mathrm{H} {}}^{\mathrm {SM}}} $ (blue), ${\Gamma _{\mathrm{H} {}}}$ unconstrained (violet), or based on on-shell 4$\ell $ only (green). Observed (expected) scans are shown with solid (dashed) curves. The horizontal lines indicate the 68% and 95% CL regions. |
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Figure 4:
Distributions of postfit ratios of the number of events in each 2$\ell $2$\nu $ and 4$\ell $ off-shell signal region bin. The ratios are taken after separate fits to the $ {\Gamma _{\mathrm{H} {}}} = $ 0 MeV hypothesis and the best overall fit. The stacked histograms display the contributions after the best fit, and the gold dashed line shows the distribution of these ratios for a fit to the $ {\Gamma _{\mathrm{H} {}}} = $ 0 MeV hypothesis. |
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Figure 5:
The Feynman diagrams contributing to the $ {\mathrm {gg}} \to {\mathrm {ZZ}} $ process at tree level are shown. The left diagram refers to the contribution involving the H boson while the right diagram is for the continuum ZZ production. Alternative crossings are ignored for illustration purposes. |
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Figure 6:
The tree-level Feynman diagrams contributing to the EW ZZ+ff production, where $f$ refers to any $\ell $, $\nu $, or $q$, are shown for the H boson -mediated contributions. Diagrams featuring VBF production are grouped together at the top, and those featuring VH production are grouped at the bottom. Alternative crossings are ignored for illustration purposes. |
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Figure 7:
The tree-level Feynman diagrams contributing to the EW ZZ+ff production, where $f$ refers to any $\ell $, $\nu $, or $q$, are shown for the continuum ZZ production contributions. Diagrams featuring VBS production are grouped together at the top, and those featuring VZZ production are grouped at the bottom. Alternative crossings are ignored for illustration purposes, and single-resonant contributions are not shown explicitly as they are not expected to contribute significantly in the off-shell region. |
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Figure 7-a:
The tree-level Feynman diagrams contributing to the EW ZZ+ff production, where $f$ refers to any $\ell $, $\nu $, or $q$, are shown for the continuum ZZ production contributions. Diagrams featuring VBS production are grouped together at the top, and those featuring VZZ production are grouped at the bottom. Alternative crossings are ignored for illustration purposes, and single-resonant contributions are not shown explicitly as they are not expected to contribute significantly in the off-shell region. |
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Figure 7-b:
The tree-level Feynman diagrams contributing to the EW ZZ+ff production, where $f$ refers to any $\ell $, $\nu $, or $q$, are shown for the continuum ZZ production contributions. Diagrams featuring VBS production are grouped together at the top, and those featuring VZZ production are grouped at the bottom. Alternative crossings are ignored for illustration purposes, and single-resonant contributions are not shown explicitly as they are not expected to contribute significantly in the off-shell region. |
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Figure 8:
The Feynman diagrams contributing to the $ {\mathrm{q} \mathrm{\bar{q}}} \to {\mathrm {ZZ}} $ and $\mathrm{q\bar{q}^\prime} \to {\mathrm {WZ}} $ processes at tree level are represented with a single diagram. These two processes constitute the major irreducible background contributions in the off-shell region. Alternative crossings are ignored for illustration purposes, and single-resonant contributions are not shown explicitly as they are not expected to contribute significantly in the off-shell region. |
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Figure 9:
Shown are the $m_{2\ell 2\nu}$ (left) and $m_{4\ell}$ distributions for the $ {\mathrm {gg}} \to 2\ell 2\nu $ and EW $ {\mathrm {ZZ}} (\to 4\ell)+\mathrm{qq}$ processes. These processes involve H boson and interfering continuum ZZ production contributions. The color code and the coupling constraints are indicated on the legends below. The acronym `PS' refers to the pure pseudoscalar H boson contribution. The distributions are shown after parton shower and inclusively in the number of generator-level jets. |
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Figure 9-a:
Shown are the $m_{2\ell 2\nu}$ (left) and $m_{4\ell}$ distributions for the $ {\mathrm {gg}} \to 2\ell 2\nu $ and EW $ {\mathrm {ZZ}} (\to 4\ell)+\mathrm{qq}$ processes. These processes involve H boson and interfering continuum ZZ production contributions. The color code and the coupling constraints are indicated on the legends below. The acronym `PS' refers to the pure pseudoscalar H boson contribution. The distributions are shown after parton shower and inclusively in the number of generator-level jets. |
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Figure 9-b:
Shown are the $m_{2\ell 2\nu}$ (left) and $m_{4\ell}$ distributions for the $ {\mathrm {gg}} \to 2\ell 2\nu $ and EW $ {\mathrm {ZZ}} (\to 4\ell)+\mathrm{qq}$ processes. These processes involve H boson and interfering continuum ZZ production contributions. The color code and the coupling constraints are indicated on the legends below. The acronym `PS' refers to the pure pseudoscalar H boson contribution. The distributions are shown after parton shower and inclusively in the number of generator-level jets. |
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Figure 10:
The distributions of SM ${{\mathcal {D}}^{\mathrm {VBF}}_{\mathrm {2jet}}}$ kinematic discriminants are shown in the 2$\ell $2$\nu $ signal region, $N_{j}\geq $ 2 category, with the decay channel ee displayed on the left and $ {\mu} {\mu} $ on the right. The stacked histograms show the predictions from simulation, and the black points show the prediction from the e$ {\mu} $ CR data. The bottom pads show the ratio of the prediction from CR data to the prediction from simulation, and the hashed band in these pads display the statistical uncertainty on the latter prediction. |
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Figure 10-a:
The distributions of SM ${{\mathcal {D}}^{\mathrm {VBF}}_{\mathrm {2jet}}}$ kinematic discriminants are shown in the 2$\ell $2$\nu $ signal region, $N_{j}\geq $ 2 category, with the decay channel ee displayed on the left and $ {\mu} {\mu} $ on the right. The stacked histograms show the predictions from simulation, and the black points show the prediction from the e$ {\mu} $ CR data. The bottom pads show the ratio of the prediction from CR data to the prediction from simulation, and the hashed band in these pads display the statistical uncertainty on the latter prediction. |
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Figure 10-b:
The distributions of SM ${{\mathcal {D}}^{\mathrm {VBF}}_{\mathrm {2jet}}}$ kinematic discriminants are shown in the 2$\ell $2$\nu $ signal region, $N_{j}\geq $ 2 category, with the decay channel ee displayed on the left and $ {\mu} {\mu} $ on the right. The stacked histograms show the predictions from simulation, and the black points show the prediction from the e$ {\mu} $ CR data. The bottom pads show the ratio of the prediction from CR data to the prediction from simulation, and the hashed band in these pads display the statistical uncertainty on the latter prediction. |
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Figure 11:
Shown are the postfit distributions of ${m_\mathrm {T}^{{\mathrm {WZ}} {}}}$ in the $N_{j}=$ 0 (bottom left), $=$ 1 (bottom middle), and $\geq $ 2 (bottom right) categories of the $ {\mathrm {WZ}} \to 3\ell 1\nu $ control region. The color legend for the stacked or dashed histograms is given on the top panel. Postfit refers to a combined 2$\ell $2$\nu $+4$\ell $ fit assuming SM H boson parameters. The middle pads on the bottom panels show the ratio of the data or dashed histograms to the stacked histogram, and the bottom pads show the relative contributions of each process in the stacked histogram. The rightmost bins show event counts in the overflow. |
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Figure 11-a:
Shown are the postfit distributions of ${m_\mathrm {T}^{{\mathrm {WZ}} {}}}$ in the $N_{j}=$ 0 (bottom left), $=$ 1 (bottom middle), and $\geq $ 2 (bottom right) categories of the $ {\mathrm {WZ}} \to 3\ell 1\nu $ control region. The color legend for the stacked or dashed histograms is given on the top panel. Postfit refers to a combined 2$\ell $2$\nu $+4$\ell $ fit assuming SM H boson parameters. The middle pads on the bottom panels show the ratio of the data or dashed histograms to the stacked histogram, and the bottom pads show the relative contributions of each process in the stacked histogram. The rightmost bins show event counts in the overflow. |
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Figure 11-b:
Shown are the postfit distributions of ${m_\mathrm {T}^{{\mathrm {WZ}} {}}}$ in the $N_{j}=$ 0 (bottom left), $=$ 1 (bottom middle), and $\geq $ 2 (bottom right) categories of the $ {\mathrm {WZ}} \to 3\ell 1\nu $ control region. The color legend for the stacked or dashed histograms is given on the top panel. Postfit refers to a combined 2$\ell $2$\nu $+4$\ell $ fit assuming SM H boson parameters. The middle pads on the bottom panels show the ratio of the data or dashed histograms to the stacked histogram, and the bottom pads show the relative contributions of each process in the stacked histogram. The rightmost bins show event counts in the overflow. |
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Figure 11-c:
Shown are the postfit distributions of ${m_\mathrm {T}^{{\mathrm {WZ}} {}}}$ in the $N_{j}=$ 0 (bottom left), $=$ 1 (bottom middle), and $\geq $ 2 (bottom right) categories of the $ {\mathrm {WZ}} \to 3\ell 1\nu $ control region. The color legend for the stacked or dashed histograms is given on the top panel. Postfit refers to a combined 2$\ell $2$\nu $+4$\ell $ fit assuming SM H boson parameters. The middle pads on the bottom panels show the ratio of the data or dashed histograms to the stacked histogram, and the bottom pads show the relative contributions of each process in the stacked histogram. The rightmost bins show event counts in the overflow. |
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Figure 11-d:
Shown are the postfit distributions of ${m_\mathrm {T}^{{\mathrm {WZ}} {}}}$ in the $N_{j}=$ 0 (bottom left), $=$ 1 (bottom middle), and $\geq $ 2 (bottom right) categories of the $ {\mathrm {WZ}} \to 3\ell 1\nu $ control region. The color legend for the stacked or dashed histograms is given on the top panel. Postfit refers to a combined 2$\ell $2$\nu $+4$\ell $ fit assuming SM H boson parameters. The middle pads on the bottom panels show the ratio of the data or dashed histograms to the stacked histogram, and the bottom pads show the relative contributions of each process in the stacked histogram. The rightmost bins show event counts in the overflow. |
png pdf |
Figure 12:
Shown are the postfit distributions of ${m_\mathrm {T}^{{\mathrm {ZZ}} {}}}$ in the $N_{j}=$ 0 (bottom left), $=$ 1 (bottom middle), and $\geq $ 2 (bottom right) categories of the 2$\ell $2$\nu $ signal region with a $ {{p_{\mathrm {T}}} ^\text {miss}} \geq $ 200 GeV requirement to enrich H boson contributions. The color legend for the stacked or dashed histograms is given on the top panel. Postfit refers to a combined 2$\ell $2$\nu $+4$\ell $ fit assuming SM H boson parameters. The middle pads on the bottom panels show the ratio of the data or dashed histograms to the stacked histogram, and the bottom pads show the relative contributions of each process in the stacked histogram. The rightmost bins show event counts in the overflow. |
png pdf |
Figure 12-a:
Shown are the postfit distributions of ${m_\mathrm {T}^{{\mathrm {ZZ}} {}}}$ in the $N_{j}=$ 0 (bottom left), $=$ 1 (bottom middle), and $\geq $ 2 (bottom right) categories of the 2$\ell $2$\nu $ signal region with a $ {{p_{\mathrm {T}}} ^\text {miss}} \geq $ 200 GeV requirement to enrich H boson contributions. The color legend for the stacked or dashed histograms is given on the top panel. Postfit refers to a combined 2$\ell $2$\nu $+4$\ell $ fit assuming SM H boson parameters. The middle pads on the bottom panels show the ratio of the data or dashed histograms to the stacked histogram, and the bottom pads show the relative contributions of each process in the stacked histogram. The rightmost bins show event counts in the overflow. |
png pdf |
Figure 12-b:
Shown are the postfit distributions of ${m_\mathrm {T}^{{\mathrm {ZZ}} {}}}$ in the $N_{j}=$ 0 (bottom left), $=$ 1 (bottom middle), and $\geq $ 2 (bottom right) categories of the 2$\ell $2$\nu $ signal region with a $ {{p_{\mathrm {T}}} ^\text {miss}} \geq $ 200 GeV requirement to enrich H boson contributions. The color legend for the stacked or dashed histograms is given on the top panel. Postfit refers to a combined 2$\ell $2$\nu $+4$\ell $ fit assuming SM H boson parameters. The middle pads on the bottom panels show the ratio of the data or dashed histograms to the stacked histogram, and the bottom pads show the relative contributions of each process in the stacked histogram. The rightmost bins show event counts in the overflow. |
png pdf |
Figure 12-c:
Shown are the postfit distributions of ${m_\mathrm {T}^{{\mathrm {ZZ}} {}}}$ in the $N_{j}=$ 0 (bottom left), $=$ 1 (bottom middle), and $\geq $ 2 (bottom right) categories of the 2$\ell $2$\nu $ signal region with a $ {{p_{\mathrm {T}}} ^\text {miss}} \geq $ 200 GeV requirement to enrich H boson contributions. The color legend for the stacked or dashed histograms is given on the top panel. Postfit refers to a combined 2$\ell $2$\nu $+4$\ell $ fit assuming SM H boson parameters. The middle pads on the bottom panels show the ratio of the data or dashed histograms to the stacked histogram, and the bottom pads show the relative contributions of each process in the stacked histogram. The rightmost bins show event counts in the overflow. |
png pdf |
Figure 12-d:
Shown are the postfit distributions of ${m_\mathrm {T}^{{\mathrm {ZZ}} {}}}$ in the $N_{j}=$ 0 (bottom left), $=$ 1 (bottom middle), and $\geq $ 2 (bottom right) categories of the 2$\ell $2$\nu $ signal region with a $ {{p_{\mathrm {T}}} ^\text {miss}} \geq $ 200 GeV requirement to enrich H boson contributions. The color legend for the stacked or dashed histograms is given on the top panel. Postfit refers to a combined 2$\ell $2$\nu $+4$\ell $ fit assuming SM H boson parameters. The middle pads on the bottom panels show the ratio of the data or dashed histograms to the stacked histogram, and the bottom pads show the relative contributions of each process in the stacked histogram. The rightmost bins show event counts in the overflow. |
| Tables | |
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Table 1:
Summary of results on the off-shell signal strength and ${\Gamma _{\mathrm{H} {}}}$. Results for ${\mu ^{\mathrm {off-shell}}}$ are with $ {R^{\mathrm {off-shell}}_{{\mathrm {V}} {}, {\mathrm {F}} {}}} $ either unconstrained or $=$ 1. Constraints on $ {\mu ^{\mathrm {off-shell}}_{{\mathrm {F}} {}}} $ and $ {\mu ^{\mathrm {off-shell}}_{{\mathrm {V}} {}}} $ are shown with the other signal strength unconstrained. Results for ${\Gamma _{\mathrm{H} {}}}$ (in units of $ MeV $) are obtained with the on-shell signal strengths unconstrained. Tests with anomalous HVV couplings are distinguished by the denoted on-shell cross section fractions. The expected values (not shown) are either unity or $ {\Gamma _{\mathrm{H} {}}} = $ 4.1 MeV. The abbreviation `c.v.' stands for `central value', and the abbreviation `(u)' stands for `unconstrained'. |
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Table 2:
Comparisons between the number of observed events in the 2$\ell $2$\nu $ channel with expectations from the SM and no-off-shell scenarios as a function of $N_j$ for low and high ${m_\mathrm {T}^{{\mathrm {ZZ}} {}}}$. An additional requirement of $ {{p_{\mathrm {T}}} ^\text {miss}} \geq $ 200 GeV has been imposed for $N_j \geq $ 2. |
| Summary |
| To summarize, we reported evidence for off-shell H boson production in the ZZ final state, excluding the no off-shell scenario at more than 99.9% confidence (3.6 standard deviations). We performed the first measurement of its total width, $\Gamma_{\mathrm{H}} =$ 3.2$_{-1.7}^{+2.4}$ MeV, with a meaningful precision in both observed and expected results, and set limits on anomalous HVV interactions. These results are based on a new analysis of the 2$\ell$2$\nu$ final state combined with previously published results for $\mathrm{ZZ }\to 4 \ell$ using up to 140 fb$^{-1}$ of pp collisions collected with the CMS detector at the LHC between 2015 and 2018. Our measurements are consistent with SM expectations. |
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