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| CMS-SMP-18-011 ; CERN-EP-2021-240 | ||
| Precision measurement of the W boson decay branching fractions in proton-proton collisions at $\sqrt{s} = $ 13 TeV | ||
| CMS Collaboration | ||
| 19 January 2022 | ||
| Phys. Rev. D 105 (2022) 072008 | ||
| Abstract: The leptonic and inclusive hadronic decay branching fractions of the W boson are measured using proton-proton collision data collected at $\sqrt{s} = $ 13 TeV by the CMS experiment at the CERN LHC, corresponding to an integrated luminosity of 35.9 fb$^{-1}$. Events characterized by the production of one or two W bosons are selected and categorized based on the multiplicity and flavor of reconstructed leptons, the number of jets, and the number of jets identified as originating from the hadronization of b quarks. A binned maximum likelihood estimate of the W boson branching fractions is performed simultaneously in each event category. The measured branching fractions of the W boson decaying into electron, muon, and tau lepton final states are (10.83 $\pm$ 0.10)%, (10.94 $\pm$ 0.08)%, and (10.77 $\pm$ 0.21)%, respectively, consistent with lepton flavor universality for the weak interaction. The average leptonic and inclusive hadronic decay branching fractions are estimated to be (10.89 $\pm$ 0.08)% and (67.32 $\pm$ 0.23)%, respectively. Based on the hadronic branching fraction, three standard model quantities are subsequently derived: the sum of squared elements in the first two rows of the Cabibbo-Kobayashi-Maskawa (CKM) matrix $\sum_{ij}|{V_{ij}} |^{2} = $ 1.984 $\pm$ 0.021, the CKM element $|{V_{\mathrm{c}\mathrm{s}}} | = $ 0.967 $\pm$ 0.011, and the strong coupling constant at the W boson mass scale, ${\alpha_S}(m^2_{\mathrm{W}}) = $ 0.095 $\pm$ 0.033. | ||
| Links: e-print arXiv:2201.07861 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Subleading electron and muon ${p_{\mathrm {T}}}$ distributions used as inputs for the binned likelihood fits for the $\mathrm{e} \mathrm{e} $ (upper) and $\mu \mu $ (lower) categories, respectively, with the requirement of one (left) or more than one (right) b-tagged jets. The lower subpanels show the ratio of data over pre-fit (dotted line) and post-fit (black circles) expectations, with associated MC statistical uncertainties (hatched area) and post-fit systematic uncertainties (shaded gray). Vertical bars on the data markers indicate statistical uncertainties. |
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Figure 1-a:
Subleading electron and muon ${p_{\mathrm {T}}}$ distributions used as inputs for the binned likelihood fits for the $\mathrm{e} \mathrm{e} $ (upper) and $\mu \mu $ (lower) categories, respectively, with the requirement of one (left) or more than one (right) b-tagged jets. The lower subpanels show the ratio of data over pre-fit (dotted line) and post-fit (black circles) expectations, with associated MC statistical uncertainties (hatched area) and post-fit systematic uncertainties (shaded gray). Vertical bars on the data markers indicate statistical uncertainties. |
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Figure 1-b:
Subleading electron and muon ${p_{\mathrm {T}}}$ distributions used as inputs for the binned likelihood fits for the $\mathrm{e} \mathrm{e} $ (upper) and $\mu \mu $ (lower) categories, respectively, with the requirement of one (left) or more than one (right) b-tagged jets. The lower subpanels show the ratio of data over pre-fit (dotted line) and post-fit (black circles) expectations, with associated MC statistical uncertainties (hatched area) and post-fit systematic uncertainties (shaded gray). Vertical bars on the data markers indicate statistical uncertainties. |
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Figure 1-c:
Subleading electron and muon ${p_{\mathrm {T}}}$ distributions used as inputs for the binned likelihood fits for the $\mathrm{e} \mathrm{e} $ (upper) and $\mu \mu $ (lower) categories, respectively, with the requirement of one (left) or more than one (right) b-tagged jets. The lower subpanels show the ratio of data over pre-fit (dotted line) and post-fit (black circles) expectations, with associated MC statistical uncertainties (hatched area) and post-fit systematic uncertainties (shaded gray). Vertical bars on the data markers indicate statistical uncertainties. |
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Figure 1-d:
Subleading electron and muon ${p_{\mathrm {T}}}$ distributions used as inputs for the binned likelihood fits for the $\mathrm{e} \mathrm{e} $ (upper) and $\mu \mu $ (lower) categories, respectively, with the requirement of one (left) or more than one (right) b-tagged jets. The lower subpanels show the ratio of data over pre-fit (dotted line) and post-fit (black circles) expectations, with associated MC statistical uncertainties (hatched area) and post-fit systematic uncertainties (shaded gray). Vertical bars on the data markers indicate statistical uncertainties. |
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Figure 2:
Subleading lepton, electron or muon, ${p_{\mathrm {T}}}$ distributions used as inputs for the binned likelihood fits for the $\mathrm{e} \mu $ categories. The different panels are obtained with the listed selection criteria on the number of jets ($N_{{\text {j}}}$) and of b-tagged jets ($N_{\mathrm{b}}$) required. The lower subpanels show the ratio of data over pre-fit expectations, with the gray histograms (hatched area) indicating MC statistical (post-fit systematic) uncertainties. Vertical bars on the data markers indicate statistical uncertainties. |
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Figure 2-a:
Subleading lepton, electron or muon, ${p_{\mathrm {T}}}$ distributions used as inputs for the binned likelihood fits for the $\mathrm{e} \mu $ categories. The different panels are obtained with the listed selection criteria on the number of jets ($N_{{\text {j}}}$) and of b-tagged jets ($N_{\mathrm{b}}$) required. The lower subpanels show the ratio of data over pre-fit expectations, with the gray histograms (hatched area) indicating MC statistical (post-fit systematic) uncertainties. Vertical bars on the data markers indicate statistical uncertainties. |
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Figure 2-b:
Subleading lepton, electron or muon, ${p_{\mathrm {T}}}$ distributions used as inputs for the binned likelihood fits for the $\mathrm{e} \mu $ categories. The different panels are obtained with the listed selection criteria on the number of jets ($N_{{\text {j}}}$) and of b-tagged jets ($N_{\mathrm{b}}$) required. The lower subpanels show the ratio of data over pre-fit expectations, with the gray histograms (hatched area) indicating MC statistical (post-fit systematic) uncertainties. Vertical bars on the data markers indicate statistical uncertainties. |
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Figure 2-c:
Subleading lepton, electron or muon, ${p_{\mathrm {T}}}$ distributions used as inputs for the binned likelihood fits for the $\mathrm{e} \mu $ categories. The different panels are obtained with the listed selection criteria on the number of jets ($N_{{\text {j}}}$) and of b-tagged jets ($N_{\mathrm{b}}$) required. The lower subpanels show the ratio of data over pre-fit expectations, with the gray histograms (hatched area) indicating MC statistical (post-fit systematic) uncertainties. Vertical bars on the data markers indicate statistical uncertainties. |
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Figure 2-d:
Subleading lepton, electron or muon, ${p_{\mathrm {T}}}$ distributions used as inputs for the binned likelihood fits for the $\mathrm{e} \mu $ categories. The different panels are obtained with the listed selection criteria on the number of jets ($N_{{\text {j}}}$) and of b-tagged jets ($N_{\mathrm{b}}$) required. The lower subpanels show the ratio of data over pre-fit expectations, with the gray histograms (hatched area) indicating MC statistical (post-fit systematic) uncertainties. Vertical bars on the data markers indicate statistical uncertainties. |
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Figure 2-e:
Subleading lepton, electron or muon, ${p_{\mathrm {T}}}$ distributions used as inputs for the binned likelihood fits for the $\mathrm{e} \mu $ categories. The different panels are obtained with the listed selection criteria on the number of jets ($N_{{\text {j}}}$) and of b-tagged jets ($N_{\mathrm{b}}$) required. The lower subpanels show the ratio of data over pre-fit expectations, with the gray histograms (hatched area) indicating MC statistical (post-fit systematic) uncertainties. Vertical bars on the data markers indicate statistical uncertainties. |
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Figure 2-f:
Subleading lepton, electron or muon, ${p_{\mathrm {T}}}$ distributions used as inputs for the binned likelihood fits for the $\mathrm{e} \mu $ categories. The different panels are obtained with the listed selection criteria on the number of jets ($N_{{\text {j}}}$) and of b-tagged jets ($N_{\mathrm{b}}$) required. The lower subpanels show the ratio of data over pre-fit expectations, with the gray histograms (hatched area) indicating MC statistical (post-fit systematic) uncertainties. Vertical bars on the data markers indicate statistical uncertainties. |
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Figure 3:
Distributions of ${\tau _\mathrm {h}}$ ${p_{\mathrm {T}}}$ used as inputs for the binned likelihood fits for the $\mathrm{e} \tau $ categories. The different panels list the varying selections on the number of jets ($N_{{\text {j}}}$) and of b-tagged jets ($N_{\mathrm{b}}$) required in each case. The lower subpanels show the ratio of data over pre-fit expectations, with the gray band (hatched area) indicating MC statistical (post-fit systematic) uncertainties. Vertical bars on the data markers indicate statistical uncertainties. |
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Figure 3-a:
Distributions of ${\tau _\mathrm {h}}$ ${p_{\mathrm {T}}}$ used as inputs for the binned likelihood fits for the $\mathrm{e} \tau $ categories. The different panels list the varying selections on the number of jets ($N_{{\text {j}}}$) and of b-tagged jets ($N_{\mathrm{b}}$) required in each case. The lower subpanels show the ratio of data over pre-fit expectations, with the gray band (hatched area) indicating MC statistical (post-fit systematic) uncertainties. Vertical bars on the data markers indicate statistical uncertainties. |
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Figure 3-b:
Distributions of ${\tau _\mathrm {h}}$ ${p_{\mathrm {T}}}$ used as inputs for the binned likelihood fits for the $\mathrm{e} \tau $ categories. The different panels list the varying selections on the number of jets ($N_{{\text {j}}}$) and of b-tagged jets ($N_{\mathrm{b}}$) required in each case. The lower subpanels show the ratio of data over pre-fit expectations, with the gray band (hatched area) indicating MC statistical (post-fit systematic) uncertainties. Vertical bars on the data markers indicate statistical uncertainties. |
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Figure 3-c:
Distributions of ${\tau _\mathrm {h}}$ ${p_{\mathrm {T}}}$ used as inputs for the binned likelihood fits for the $\mathrm{e} \tau $ categories. The different panels list the varying selections on the number of jets ($N_{{\text {j}}}$) and of b-tagged jets ($N_{\mathrm{b}}$) required in each case. The lower subpanels show the ratio of data over pre-fit expectations, with the gray band (hatched area) indicating MC statistical (post-fit systematic) uncertainties. Vertical bars on the data markers indicate statistical uncertainties. |
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Figure 3-d:
Distributions of ${\tau _\mathrm {h}}$ ${p_{\mathrm {T}}}$ used as inputs for the binned likelihood fits for the $\mathrm{e} \tau $ categories. The different panels list the varying selections on the number of jets ($N_{{\text {j}}}$) and of b-tagged jets ($N_{\mathrm{b}}$) required in each case. The lower subpanels show the ratio of data over pre-fit expectations, with the gray band (hatched area) indicating MC statistical (post-fit systematic) uncertainties. Vertical bars on the data markers indicate statistical uncertainties. |
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Figure 3-e:
Distributions of ${\tau _\mathrm {h}}$ ${p_{\mathrm {T}}}$ used as inputs for the binned likelihood fits for the $\mathrm{e} \tau $ categories. The different panels list the varying selections on the number of jets ($N_{{\text {j}}}$) and of b-tagged jets ($N_{\mathrm{b}}$) required in each case. The lower subpanels show the ratio of data over pre-fit expectations, with the gray band (hatched area) indicating MC statistical (post-fit systematic) uncertainties. Vertical bars on the data markers indicate statistical uncertainties. |
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Figure 3-f:
Distributions of ${\tau _\mathrm {h}}$ ${p_{\mathrm {T}}}$ used as inputs for the binned likelihood fits for the $\mathrm{e} \tau $ categories. The different panels list the varying selections on the number of jets ($N_{{\text {j}}}$) and of b-tagged jets ($N_{\mathrm{b}}$) required in each case. The lower subpanels show the ratio of data over pre-fit expectations, with the gray band (hatched area) indicating MC statistical (post-fit systematic) uncertainties. Vertical bars on the data markers indicate statistical uncertainties. |
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Figure 3-g:
Distributions of ${\tau _\mathrm {h}}$ ${p_{\mathrm {T}}}$ used as inputs for the binned likelihood fits for the $\mathrm{e} \tau $ categories. The different panels list the varying selections on the number of jets ($N_{{\text {j}}}$) and of b-tagged jets ($N_{\mathrm{b}}$) required in each case. The lower subpanels show the ratio of data over pre-fit expectations, with the gray band (hatched area) indicating MC statistical (post-fit systematic) uncertainties. Vertical bars on the data markers indicate statistical uncertainties. |
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Figure 3-h:
Distributions of ${\tau _\mathrm {h}}$ ${p_{\mathrm {T}}}$ used as inputs for the binned likelihood fits for the $\mathrm{e} \tau $ categories. The different panels list the varying selections on the number of jets ($N_{{\text {j}}}$) and of b-tagged jets ($N_{\mathrm{b}}$) required in each case. The lower subpanels show the ratio of data over pre-fit expectations, with the gray band (hatched area) indicating MC statistical (post-fit systematic) uncertainties. Vertical bars on the data markers indicate statistical uncertainties. |
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Figure 4:
Distributions of ${\tau _\mathrm {h}}$ ${p_{\mathrm {T}}}$ used as inputs for the binned likelihood fits for the $\mu \tau $ categories. The different panels list the varying selections on the number of jets ($N_{{\text {j}}}$) and of b-tagged jets ($N_{\mathrm{b}}$) required in each case. The lower subpanels show the ratio of data over pre-fit expectations, with the gray histograms (hatched area) indicating MC statistical (post-fit systematic) uncertainties. Vertical bars on the data markers indicate statistical uncertainties. |
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Figure 4-a:
Distributions of ${\tau _\mathrm {h}}$ ${p_{\mathrm {T}}}$ used as inputs for the binned likelihood fits for the $\mu \tau $ categories. The different panels list the varying selections on the number of jets ($N_{{\text {j}}}$) and of b-tagged jets ($N_{\mathrm{b}}$) required in each case. The lower subpanels show the ratio of data over pre-fit expectations, with the gray histograms (hatched area) indicating MC statistical (post-fit systematic) uncertainties. Vertical bars on the data markers indicate statistical uncertainties. |
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Figure 4-b:
Distributions of ${\tau _\mathrm {h}}$ ${p_{\mathrm {T}}}$ used as inputs for the binned likelihood fits for the $\mu \tau $ categories. The different panels list the varying selections on the number of jets ($N_{{\text {j}}}$) and of b-tagged jets ($N_{\mathrm{b}}$) required in each case. The lower subpanels show the ratio of data over pre-fit expectations, with the gray histograms (hatched area) indicating MC statistical (post-fit systematic) uncertainties. Vertical bars on the data markers indicate statistical uncertainties. |
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Figure 4-c:
Distributions of ${\tau _\mathrm {h}}$ ${p_{\mathrm {T}}}$ used as inputs for the binned likelihood fits for the $\mu \tau $ categories. The different panels list the varying selections on the number of jets ($N_{{\text {j}}}$) and of b-tagged jets ($N_{\mathrm{b}}$) required in each case. The lower subpanels show the ratio of data over pre-fit expectations, with the gray histograms (hatched area) indicating MC statistical (post-fit systematic) uncertainties. Vertical bars on the data markers indicate statistical uncertainties. |
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Figure 4-d:
Distributions of ${\tau _\mathrm {h}}$ ${p_{\mathrm {T}}}$ used as inputs for the binned likelihood fits for the $\mu \tau $ categories. The different panels list the varying selections on the number of jets ($N_{{\text {j}}}$) and of b-tagged jets ($N_{\mathrm{b}}$) required in each case. The lower subpanels show the ratio of data over pre-fit expectations, with the gray histograms (hatched area) indicating MC statistical (post-fit systematic) uncertainties. Vertical bars on the data markers indicate statistical uncertainties. |
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Figure 4-e:
Distributions of ${\tau _\mathrm {h}}$ ${p_{\mathrm {T}}}$ used as inputs for the binned likelihood fits for the $\mu \tau $ categories. The different panels list the varying selections on the number of jets ($N_{{\text {j}}}$) and of b-tagged jets ($N_{\mathrm{b}}$) required in each case. The lower subpanels show the ratio of data over pre-fit expectations, with the gray histograms (hatched area) indicating MC statistical (post-fit systematic) uncertainties. Vertical bars on the data markers indicate statistical uncertainties. |
png pdf |
Figure 4-f:
Distributions of ${\tau _\mathrm {h}}$ ${p_{\mathrm {T}}}$ used as inputs for the binned likelihood fits for the $\mu \tau $ categories. The different panels list the varying selections on the number of jets ($N_{{\text {j}}}$) and of b-tagged jets ($N_{\mathrm{b}}$) required in each case. The lower subpanels show the ratio of data over pre-fit expectations, with the gray histograms (hatched area) indicating MC statistical (post-fit systematic) uncertainties. Vertical bars on the data markers indicate statistical uncertainties. |
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Figure 4-g:
Distributions of ${\tau _\mathrm {h}}$ ${p_{\mathrm {T}}}$ used as inputs for the binned likelihood fits for the $\mu \tau $ categories. The different panels list the varying selections on the number of jets ($N_{{\text {j}}}$) and of b-tagged jets ($N_{\mathrm{b}}$) required in each case. The lower subpanels show the ratio of data over pre-fit expectations, with the gray histograms (hatched area) indicating MC statistical (post-fit systematic) uncertainties. Vertical bars on the data markers indicate statistical uncertainties. |
png pdf |
Figure 4-h:
Distributions of ${\tau _\mathrm {h}}$ ${p_{\mathrm {T}}}$ used as inputs for the binned likelihood fits for the $\mu \tau $ categories. The different panels list the varying selections on the number of jets ($N_{{\text {j}}}$) and of b-tagged jets ($N_{\mathrm{b}}$) required in each case. The lower subpanels show the ratio of data over pre-fit expectations, with the gray histograms (hatched area) indicating MC statistical (post-fit systematic) uncertainties. Vertical bars on the data markers indicate statistical uncertainties. |
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Figure 5:
Distributions of electron or muon ${p_{\mathrm {T}}}$ used as inputs for the binned likelihood fits for the $\mathrm{e} {\text {h}} $ (upper) and $\mu {\text {h}} $ (lower) categories, respectively, with the requirement of one (left) or more than one (right) b-tagged jets. The lower subpanels show the ratio of data over pre-fit expectations, with the gray histograms (hatched area) indicating MC statistical (post-fit systematic) uncertainties. Vertical bars on the data markers indicate statistical uncertainties. |
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Figure 5-a:
Distributions of electron or muon ${p_{\mathrm {T}}}$ used as inputs for the binned likelihood fits for the $\mathrm{e} {\text {h}} $ (upper) and $\mu {\text {h}} $ (lower) categories, respectively, with the requirement of one (left) or more than one (right) b-tagged jets. The lower subpanels show the ratio of data over pre-fit expectations, with the gray histograms (hatched area) indicating MC statistical (post-fit systematic) uncertainties. Vertical bars on the data markers indicate statistical uncertainties. |
png pdf |
Figure 5-b:
Distributions of electron or muon ${p_{\mathrm {T}}}$ used as inputs for the binned likelihood fits for the $\mathrm{e} {\text {h}} $ (upper) and $\mu {\text {h}} $ (lower) categories, respectively, with the requirement of one (left) or more than one (right) b-tagged jets. The lower subpanels show the ratio of data over pre-fit expectations, with the gray histograms (hatched area) indicating MC statistical (post-fit systematic) uncertainties. Vertical bars on the data markers indicate statistical uncertainties. |
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Figure 5-c:
Distributions of electron or muon ${p_{\mathrm {T}}}$ used as inputs for the binned likelihood fits for the $\mathrm{e} {\text {h}} $ (upper) and $\mu {\text {h}} $ (lower) categories, respectively, with the requirement of one (left) or more than one (right) b-tagged jets. The lower subpanels show the ratio of data over pre-fit expectations, with the gray histograms (hatched area) indicating MC statistical (post-fit systematic) uncertainties. Vertical bars on the data markers indicate statistical uncertainties. |
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Figure 5-d:
Distributions of electron or muon ${p_{\mathrm {T}}}$ used as inputs for the binned likelihood fits for the $\mathrm{e} {\text {h}} $ (upper) and $\mu {\text {h}} $ (lower) categories, respectively, with the requirement of one (left) or more than one (right) b-tagged jets. The lower subpanels show the ratio of data over pre-fit expectations, with the gray histograms (hatched area) indicating MC statistical (post-fit systematic) uncertainties. Vertical bars on the data markers indicate statistical uncertainties. |
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Figure 6:
Summary of the measured values of the W leptonic branching fractions compared with the corresponding LEP results [8,9]. The vertical green-yellow band shows the extracted W leptonic branching fraction assuming LFU (the hatched band shows the corresponding LEP result). The horizontal error bars on the data points indicate their total uncertainty. |
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Figure 7:
Two-dimensional distributions of pairs of W leptonic branching fractions derived here compared with the corresponding LEP results [8,9] and to the SM expectation. The green (darker) and yellow (lighter) bands (dashed lines for the LEP results) correspond to the 68% and 95% CL, respectively, for the resulting two-dimensional Gaussian distribution. |
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Figure 8:
Correlation matrix between the four W boson decay branching fraction components extracted in this work. |
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Figure 9:
Two-dimensional distribution of the ratio ${R_{\tau /\mathrm{e}}}$ versus ${R_{\tau /\mu}}$, compared with the corresponding LEP [8,9] and ATLAS [13] results and with the SM expectation. The green and yellow bands (dashed lines for the LEP results) correspond to the 68% and 95% CL, respectively, for the resulting two-dimensional Gaussian distribution. The corresponding 68% CL one-dimensional projections (black error bars) are also overlaid for a better visual comparison with the ATLAS ${R_{\tau /\mu}}$ result. |
| Tables | |
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Table 1:
Categorization of events based on the triggering lepton, the number of reconstructed and selected leptons ($N_{\mathrm{e}}$, $N_{\mu}$, $N_{{\tau _\mathrm {h}}}$), number of jets ($N_ {\text {j}} $), and number of b-tagged jets ($N_{\mathrm{b}}$). Kinematic requirements of the leptons and jets are listed in the fourth column. Categories with two leptons in the final state require the selected leptons to have opposite signs. The second-to-last column lists the targeted W boson branching fractions, and the last column provides the approximate number of W decays collected in each category. |
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Table 2:
Categorization of events with electrons, muons, and ${\tau _\mathrm {h}}$ passing the reconstruction criteria, based on their jet and b-tagged jet multiplicities, used to define signal-enriched and control regions. Events in the $\mathrm{e} {\tau _\mathrm {h}} $ and $\mu {\tau _\mathrm {h}} $ categories with at least one jet that is not b-tagged are additionally required to satisfy 40 $\leq m_{\ell {\tau _\mathrm {h}}} \leq $ 100 GeV, $\Delta \phi (\ell, {\tau _\mathrm {h}}) > $ 2.5, and $ {m_{\mathrm {T}}} ^\ell < $ 60 GeV. |
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Table 3:
Summary of the impacts of each source of uncertainty (quoted as a percent of the total systematic uncertainty) for each W branching fraction. Whenever multiple NPs impact a common source of systematic uncertainty, each component is varied independently and the range of impacts is given. |
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Table 4:
Values of the W boson decay branching fractions measured here compared with the corresponding LEP measurements [8,9]. The lower rows list the average leptonic and inclusive hadronic W branching fractions derived assuming LFU. The first and second uncertainties quoted for each branching fraction correspond to statistical and systematic sources, respectively. |
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Table 5:
Ratios of different leptonic branching fractions, $R_{\mu /\mathrm{e}} = \mathcal {B}(\mathrm{W} \to \mu \overline{\nu}_{\mu})/\mathcal {B}(\mathrm{W} \to \mathrm{e} \overline{\nu}_{\mathrm{e}})$, $R_{\tau /\mathrm{e}} = \mathcal {B}(\mathrm{W} \to \tau \overline{\nu}_{\tau})/\mathcal {B}(\mathrm{W} \to \mathrm{e} \overline{\nu}_{\mathrm{e}})$, and $R_{\tau /\mu} = \mathcal {B}(\mathrm{W} \to \tau \overline{\nu}_{\tau})/\mathcal {B}(\mathrm{W} \to \mu \overline{\nu}_{\mu})$, measured here compared with the values obtained by other LEP [8], LHC [16,17,13], and Tevatron [14,15] experiments. |
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Table 6:
Values of the QCD coupling constant at the W mass, the charm-strange CKM mixing element, and the squared sum of the first two rows of the CKM matrix, derived in this work. |
| Summary |
|
A precise measurement of the three leptonic decay branching fractions of the W boson has been presented, as well as the average leptonic and inclusive hadronic branching fractions assuming lepton flavor universality (LFU). The analysis is based on a data sample of pp collisions at a center-of-mass energy of 13 TeV corresponding to an integrated luminosity of 35.9 fb$^{-1}$ recorded by the CMS experiment. Events with one or two W bosons produced are collected using single-charged-lepton triggers that require at least one prompt electron or muon with large transverse momentum. The extraction of the W boson leptonic branching fractions is performed through a binned maximum likelihood fit of events split into multiple categories defined based on the multiplicity and flavor of reconstructed leptons, the number of jets, and the number of jets identified as originating from the hadronization of b quarks. The measured branching fractions for the decay of the W boson into electrons, muons, tau leptons, and hadrons are (10.83 $\pm$ 0.10)%, (10.94 $\pm$ 0.08)%, (10.77 $\pm$ 0.21)%, and (67.46 $\pm$ 0.28)%, respectively. These results are consistent with the LFU hypothesis for the weak interaction, and are more precise than previous measurements based on data collected by the LEP experiments. Fitting the data assuming LFU provides values of (10.89 $\pm$ 0.08)% and (67.32 $\pm$ 0.23)%, respectively, for the average leptonic and inclusive hadronic branching fractions of the W boson. The comparison of the ratio of hadronic-to-leptonic branching fractions to the theoretical prediction is used to derive other standard model quantities. A value of the strong coupling constant at the W boson mass scale of ${\alpha_S}(m^{2}_\mathrm{W}) = $ 0.095 $\pm$ 0.033 is obtained which, although not competitive compared with the current world average, confirms the usefulness of the W boson decays to constrain this fundamental standard model parameter at future colliders. Using the world average value of ${\alpha_S}(m^{2}_\mathrm{W})$, the sum of the square of the elements in the first two rows of the Cabibbo-Kobayashi-Maskawa (CKM) matrix is $\sum_{ij}|V_{{ij}}|^{2} = $ 1.984 $\pm$ 0.021, providing a precise check of CKM unitarity. From this sum and using the world-average values of the other relevant CKM matrix elements, a value of $|V_{{\mathrm{c}\mathrm{s}}}| = $ 0.967 $\pm$ 0.011 is determined, which is as precise as the current $|V_{{\mathrm{c}\mathrm{s}}}| = $ 0.987 $\pm$ 0.011 result obtained from direct D meson decay data. |
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