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| CMS-HIG-18-031 ; CERN-EP-2019-257 | ||
| A search for the standard model Higgs boson decaying to charm quarks | ||
| CMS Collaboration | ||
| 3 December 2019 | ||
| JHEP 03 (2020) 131 | ||
| Abstract: A direct search for the standard model Higgs boson, H, produced in association with a vector boson, V (W or Z), and decaying to a charm quark pair is presented. The search uses a data set of proton-proton collisions corresponding to an integrated luminosity of 35.9 fb$^{-1}$, collected by the CMS experiment at the LHC in 2016, at a centre-of-mass energy of 13 TeV. The search is carried out in mutually exclusive channels targeting specific decays of the vector bosons: $\mathrm{W}\to \ell \nu$, $\mathrm{Z}\to \ell\ell$, and $\mathrm{Z}\to \nu\nu$, where $\ell$ is an electron or a muon. To fully exploit the topology of the H boson decay, two strategies are followed. In the first one, targeting lower vector boson transverse momentum, the H boson candidate is reconstructed via two resolved jets arising from the two charm quarks from the H boson decay. A second strategy identifies the case where the two charm quark jets from the H boson decay merge to form a single jet, which generally only occurs when the vector boson has higher transverse momentum. Both strategies make use of novel methods for charm jet identification, while jet substructure techniques are also exploited to suppress the background in the merged-jet topology. The two analyses are combined to yield a 95% confidence level observed (expected) upper limit on the cross section $\sigma\left({{\mathrm{V}}\mathrm{H}} \right)\mathcal{B}\left(\mathrm{H} \to \mathrm{c\bar{c}} \right)$ of 4.5 (2.4$^{+1.0}_{-0.7}$) pb, corresponding to 70 (37) times the standard model prediction. | ||
| Links: e-print arXiv:1912.01662 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Efficiency to tag a c jet as a function of the b jet and light-flavour quark or gluon jet mistag rates. The working point adopted in the resolved-jet topology analysis to select the leading $\textit{CvsL}$ jets is shown with a white cross. The white lines correspond to c jet iso-efficiency curves. The plot makes use of jets with $ {p_{\mathrm {T}}} > $ 20 GeV that have been clustered with AK4 algorithm in a simulated ${\mathrm{t} \mathrm{\bar{t}}}$+jets sample before application of data-to-simulation reshaping scale factors. |
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Figure 2:
Post-fit $\textit {CvsB}_{\text {min}}$ distributions in the CC (left panel) and HF (right panel) control regions for the 2L (${\mathrm{Z} (\mu \mu})$) low- ${{p_{\mathrm {T}}} (\mathrm{V})}$, 2L (${\mathrm{Z} (\mathrm{e} \mathrm{e})}$) high-$ {{p_{\mathrm {T}}} (\mathrm{V})}$, 1L (${\mathrm{W} (\mu \nu)}$), and 0L channels. |
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Figure 2-a:
Post-fit $\textit {CvsB}_{\text {min}}$ distributions in the CC (left panel) and HF (right panel) control regions for the 2L (${\mathrm{Z} (\mu \mu})$) low- ${{p_{\mathrm {T}}} (\mathrm{V})}$, 2L (${\mathrm{Z} (\mathrm{e} \mathrm{e})}$) high-$ {{p_{\mathrm {T}}} (\mathrm{V})}$, 1L (${\mathrm{W} (\mu \nu)}$), and 0L channels. |
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Figure 2-b:
Post-fit $\textit {CvsB}_{\text {min}}$ distributions in the CC (left panel) and HF (right panel) control regions for the 2L (${\mathrm{Z} (\mu \mu})$) low- ${{p_{\mathrm {T}}} (\mathrm{V})}$, 2L (${\mathrm{Z} (\mathrm{e} \mathrm{e})}$) high-$ {{p_{\mathrm {T}}} (\mathrm{V})}$, 1L (${\mathrm{W} (\mu \nu)}$), and 0L channels. |
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Figure 2-c:
Post-fit $\textit {CvsB}_{\text {min}}$ distributions in the CC (left panel) and HF (right panel) control regions for the 2L (${\mathrm{Z} (\mu \mu})$) low- ${{p_{\mathrm {T}}} (\mathrm{V})}$, 2L (${\mathrm{Z} (\mathrm{e} \mathrm{e})}$) high-$ {{p_{\mathrm {T}}} (\mathrm{V})}$, 1L (${\mathrm{W} (\mu \nu)}$), and 0L channels. |
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Figure 2-d:
Post-fit $\textit {CvsB}_{\text {min}}$ distributions in the CC (left panel) and HF (right panel) control regions for the 2L (${\mathrm{Z} (\mu \mu})$) low- ${{p_{\mathrm {T}}} (\mathrm{V})}$, 2L (${\mathrm{Z} (\mathrm{e} \mathrm{e})}$) high-$ {{p_{\mathrm {T}}} (\mathrm{V})}$, 1L (${\mathrm{W} (\mu \nu)}$), and 0L channels. |
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Figure 2-e:
Post-fit $\textit {CvsB}_{\text {min}}$ distributions in the CC (left panel) and HF (right panel) control regions for the 2L (${\mathrm{Z} (\mu \mu})$) low- ${{p_{\mathrm {T}}} (\mathrm{V})}$, 2L (${\mathrm{Z} (\mathrm{e} \mathrm{e})}$) high-$ {{p_{\mathrm {T}}} (\mathrm{V})}$, 1L (${\mathrm{W} (\mu \nu)}$), and 0L channels. |
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Figure 2-f:
Post-fit $\textit {CvsB}_{\text {min}}$ distributions in the CC (left panel) and HF (right panel) control regions for the 2L (${\mathrm{Z} (\mu \mu})$) low- ${{p_{\mathrm {T}}} (\mathrm{V})}$, 2L (${\mathrm{Z} (\mathrm{e} \mathrm{e})}$) high-$ {{p_{\mathrm {T}}} (\mathrm{V})}$, 1L (${\mathrm{W} (\mu \nu)}$), and 0L channels. |
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Figure 2-g:
Post-fit $\textit {CvsB}_{\text {min}}$ distributions in the CC (left panel) and HF (right panel) control regions for the 2L (${\mathrm{Z} (\mu \mu})$) low- ${{p_{\mathrm {T}}} (\mathrm{V})}$, 2L (${\mathrm{Z} (\mathrm{e} \mathrm{e})}$) high-$ {{p_{\mathrm {T}}} (\mathrm{V})}$, 1L (${\mathrm{W} (\mu \nu)}$), and 0L channels. |
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Figure 2-h:
Post-fit $\textit {CvsB}_{\text {min}}$ distributions in the CC (left panel) and HF (right panel) control regions for the 2L (${\mathrm{Z} (\mu \mu})$) low- ${{p_{\mathrm {T}}} (\mathrm{V})}$, 2L (${\mathrm{Z} (\mathrm{e} \mathrm{e})}$) high-$ {{p_{\mathrm {T}}} (\mathrm{V})}$, 1L (${\mathrm{W} (\mu \nu)}$), and 0L channels. |
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Figure 3:
The performance of the $\mathrm{c} \mathrm{\bar{c}} $ discriminant to identify a $\mathrm{c} \mathrm{\bar{c}} $ pair in terms of receiver operating characteristic curves, for large-$R$\ jets with $ {p_{\mathrm {T}}} > $ 200 GeV, before the application of data-to-simulation scale factors. Left: the efficiency to correctly identify a pair of c quarks from H boson decay vs. the efficiency of misidentifying quarks from the V+jets process. Right: the efficiency to correctly identify a pair of c quarks from H boson decay vs. the efficiency of misidentifying a pair of b quarks from H boson decay. The gray stars and crosses on the ROC curves represent the three working points used in the merged-jet topology analysis. |
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Figure 3-a:
The performance of the $\mathrm{c} \mathrm{\bar{c}} $ discriminant to identify a $\mathrm{c} \mathrm{\bar{c}} $ pair in terms of receiver operating characteristic curves, for large-$R$\ jets with $ {p_{\mathrm {T}}} > $ 200 GeV, before the application of data-to-simulation scale factors. Left: the efficiency to correctly identify a pair of c quarks from H boson decay vs. the efficiency of misidentifying quarks from the V+jets process. Right: the efficiency to correctly identify a pair of c quarks from H boson decay vs. the efficiency of misidentifying a pair of b quarks from H boson decay. The gray stars and crosses on the ROC curves represent the three working points used in the merged-jet topology analysis. |
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Figure 3-b:
The performance of the $\mathrm{c} \mathrm{\bar{c}} $ discriminant to identify a $\mathrm{c} \mathrm{\bar{c}} $ pair in terms of receiver operating characteristic curves, for large-$R$\ jets with $ {p_{\mathrm {T}}} > $ 200 GeV, before the application of data-to-simulation scale factors. Left: the efficiency to correctly identify a pair of c quarks from H boson decay vs. the efficiency of misidentifying quarks from the V+jets process. Right: the efficiency to correctly identify a pair of c quarks from H boson decay vs. the efficiency of misidentifying a pair of b quarks from H boson decay. The gray stars and crosses on the ROC curves represent the three working points used in the merged-jet topology analysis. |
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Figure 4:
The ${\mathrm{V} \mathrm{H} (\mathrm{H} \to \mathrm{c\bar{c}})}$ signal and background distributions of the kinematic BDT output (left), and the $\mathrm{c} \mathrm{\bar{c}} $ discriminant in events with BDT values greater than 0.5 (right), in the 0L (upper), 1L (middle) and 2L (lower) channels. The ${\mathrm{V} \mathrm{H} (\mathrm{H} \to \mathrm{c\bar{c}})}$ signal is normalised to the sum of all backgrounds. The ${\mathrm{V} \mathrm{H} (\mathrm{H} \to \mathrm{b} \mathrm{\bar{b}})} $ contribution, similarly normalised, is also shown. |
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Figure 4-a:
The ${\mathrm{V} \mathrm{H} (\mathrm{H} \to \mathrm{c\bar{c}})}$ signal and background distributions of the kinematic BDT output (left), and the $\mathrm{c} \mathrm{\bar{c}} $ discriminant in events with BDT values greater than 0.5 (right), in the 0L (upper), 1L (middle) and 2L (lower) channels. The ${\mathrm{V} \mathrm{H} (\mathrm{H} \to \mathrm{c\bar{c}})}$ signal is normalised to the sum of all backgrounds. The ${\mathrm{V} \mathrm{H} (\mathrm{H} \to \mathrm{b} \mathrm{\bar{b}})} $ contribution, similarly normalised, is also shown. |
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Figure 4-b:
The ${\mathrm{V} \mathrm{H} (\mathrm{H} \to \mathrm{c\bar{c}})}$ signal and background distributions of the kinematic BDT output (left), and the $\mathrm{c} \mathrm{\bar{c}} $ discriminant in events with BDT values greater than 0.5 (right), in the 0L (upper), 1L (middle) and 2L (lower) channels. The ${\mathrm{V} \mathrm{H} (\mathrm{H} \to \mathrm{c\bar{c}})}$ signal is normalised to the sum of all backgrounds. The ${\mathrm{V} \mathrm{H} (\mathrm{H} \to \mathrm{b} \mathrm{\bar{b}})} $ contribution, similarly normalised, is also shown. |
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Figure 4-c:
The ${\mathrm{V} \mathrm{H} (\mathrm{H} \to \mathrm{c\bar{c}})}$ signal and background distributions of the kinematic BDT output (left), and the $\mathrm{c} \mathrm{\bar{c}} $ discriminant in events with BDT values greater than 0.5 (right), in the 0L (upper), 1L (middle) and 2L (lower) channels. The ${\mathrm{V} \mathrm{H} (\mathrm{H} \to \mathrm{c\bar{c}})}$ signal is normalised to the sum of all backgrounds. The ${\mathrm{V} \mathrm{H} (\mathrm{H} \to \mathrm{b} \mathrm{\bar{b}})} $ contribution, similarly normalised, is also shown. |
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Figure 4-d:
The ${\mathrm{V} \mathrm{H} (\mathrm{H} \to \mathrm{c\bar{c}})}$ signal and background distributions of the kinematic BDT output (left), and the $\mathrm{c} \mathrm{\bar{c}} $ discriminant in events with BDT values greater than 0.5 (right), in the 0L (upper), 1L (middle) and 2L (lower) channels. The ${\mathrm{V} \mathrm{H} (\mathrm{H} \to \mathrm{c\bar{c}})}$ signal is normalised to the sum of all backgrounds. The ${\mathrm{V} \mathrm{H} (\mathrm{H} \to \mathrm{b} \mathrm{\bar{b}})} $ contribution, similarly normalised, is also shown. |
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Figure 4-e:
The ${\mathrm{V} \mathrm{H} (\mathrm{H} \to \mathrm{c\bar{c}})}$ signal and background distributions of the kinematic BDT output (left), and the $\mathrm{c} \mathrm{\bar{c}} $ discriminant in events with BDT values greater than 0.5 (right), in the 0L (upper), 1L (middle) and 2L (lower) channels. The ${\mathrm{V} \mathrm{H} (\mathrm{H} \to \mathrm{c\bar{c}})}$ signal is normalised to the sum of all backgrounds. The ${\mathrm{V} \mathrm{H} (\mathrm{H} \to \mathrm{b} \mathrm{\bar{b}})} $ contribution, similarly normalised, is also shown. |
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Figure 4-f:
The ${\mathrm{V} \mathrm{H} (\mathrm{H} \to \mathrm{c\bar{c}})}$ signal and background distributions of the kinematic BDT output (left), and the $\mathrm{c} \mathrm{\bar{c}} $ discriminant in events with BDT values greater than 0.5 (right), in the 0L (upper), 1L (middle) and 2L (lower) channels. The ${\mathrm{V} \mathrm{H} (\mathrm{H} \to \mathrm{c\bar{c}})}$ signal is normalised to the sum of all backgrounds. The ${\mathrm{V} \mathrm{H} (\mathrm{H} \to \mathrm{b} \mathrm{\bar{b}})} $ contribution, similarly normalised, is also shown. |
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Figure 5:
Post-fit distributions of the BDT score in the signal region of the resolved-jet topology analysis for the 2L low-$ {{p_{\mathrm {T}}} (\mathrm{V})}, 2L high- {{p_{\mathrm {T}}} (\mathrm{V})}$, 1L, and 0L channels. The plain red histograms represent the signal contribution normalized by the post-fit value of $\mu _{{\mathrm{V} \mathrm{H} (\mathrm{H} \to \mathrm{c\bar{c}})}}$, while the red line histograms show the expected signal contribution multiplied by a factor 100. |
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Figure 5-a:
Post-fit distributions of the BDT score in the signal region of the resolved-jet topology analysis for the 2L low-$ {{p_{\mathrm {T}}} (\mathrm{V})}, 2L high- {{p_{\mathrm {T}}} (\mathrm{V})}$, 1L, and 0L channels. The plain red histograms represent the signal contribution normalized by the post-fit value of $\mu _{{\mathrm{V} \mathrm{H} (\mathrm{H} \to \mathrm{c\bar{c}})}}$, while the red line histograms show the expected signal contribution multiplied by a factor 100. |
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Figure 5-b:
Post-fit distributions of the BDT score in the signal region of the resolved-jet topology analysis for the 2L low-$ {{p_{\mathrm {T}}} (\mathrm{V})}, 2L high- {{p_{\mathrm {T}}} (\mathrm{V})}$, 1L, and 0L channels. The plain red histograms represent the signal contribution normalized by the post-fit value of $\mu _{{\mathrm{V} \mathrm{H} (\mathrm{H} \to \mathrm{c\bar{c}})}}$, while the red line histograms show the expected signal contribution multiplied by a factor 100. |
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Figure 5-c:
Post-fit distributions of the BDT score in the signal region of the resolved-jet topology analysis for the 2L low-$ {{p_{\mathrm {T}}} (\mathrm{V})}, 2L high- {{p_{\mathrm {T}}} (\mathrm{V})}$, 1L, and 0L channels. The plain red histograms represent the signal contribution normalized by the post-fit value of $\mu _{{\mathrm{V} \mathrm{H} (\mathrm{H} \to \mathrm{c\bar{c}})}}$, while the red line histograms show the expected signal contribution multiplied by a factor 100. |
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Figure 5-d:
Post-fit distributions of the BDT score in the signal region of the resolved-jet topology analysis for the 2L low-$ {{p_{\mathrm {T}}} (\mathrm{V})}, 2L high- {{p_{\mathrm {T}}} (\mathrm{V})}$, 1L, and 0L channels. The plain red histograms represent the signal contribution normalized by the post-fit value of $\mu _{{\mathrm{V} \mathrm{H} (\mathrm{H} \to \mathrm{c\bar{c}})}}$, while the red line histograms show the expected signal contribution multiplied by a factor 100. |
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Figure 5-e:
Post-fit distributions of the BDT score in the signal region of the resolved-jet topology analysis for the 2L low-$ {{p_{\mathrm {T}}} (\mathrm{V})}, 2L high- {{p_{\mathrm {T}}} (\mathrm{V})}$, 1L, and 0L channels. The plain red histograms represent the signal contribution normalized by the post-fit value of $\mu _{{\mathrm{V} \mathrm{H} (\mathrm{H} \to \mathrm{c\bar{c}})}}$, while the red line histograms show the expected signal contribution multiplied by a factor 100. |
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Figure 5-f:
Post-fit distributions of the BDT score in the signal region of the resolved-jet topology analysis for the 2L low-$ {{p_{\mathrm {T}}} (\mathrm{V})}, 2L high- {{p_{\mathrm {T}}} (\mathrm{V})}$, 1L, and 0L channels. The plain red histograms represent the signal contribution normalized by the post-fit value of $\mu _{{\mathrm{V} \mathrm{H} (\mathrm{H} \to \mathrm{c\bar{c}})}}$, while the red line histograms show the expected signal contribution multiplied by a factor 100. |
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Figure 5-g:
Post-fit distributions of the BDT score in the signal region of the resolved-jet topology analysis for the 2L low-$ {{p_{\mathrm {T}}} (\mathrm{V})}, 2L high- {{p_{\mathrm {T}}} (\mathrm{V})}$, 1L, and 0L channels. The plain red histograms represent the signal contribution normalized by the post-fit value of $\mu _{{\mathrm{V} \mathrm{H} (\mathrm{H} \to \mathrm{c\bar{c}})}}$, while the red line histograms show the expected signal contribution multiplied by a factor 100. |
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Figure 6:
The ${m_{\text {SD}}}$ distribution of H in data and simulation in the merged-jet topology analysis signal regions after the maximum likelihood fit, for events in the high purity category. Upper row: 2L channel, electrons (left) and muons (right); middle row: 1L channel, electron (left) and muon (right); lower row: 0L channel. The plain red histograms represent the signal contribution normalized by the post-fit value of $\mu _{{\mathrm{V} \mathrm{H} (\mathrm{H} \to \mathrm{c\bar{c}})}}$, while the red line histograms show the expected signal contribution multiplied by a factor 100. |
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Figure 6-a:
The ${m_{\text {SD}}}$ distribution of H in data and simulation in the merged-jet topology analysis signal regions after the maximum likelihood fit, for events in the high purity category. Upper row: 2L channel, electrons (left) and muons (right); middle row: 1L channel, electron (left) and muon (right); lower row: 0L channel. The plain red histograms represent the signal contribution normalized by the post-fit value of $\mu _{{\mathrm{V} \mathrm{H} (\mathrm{H} \to \mathrm{c\bar{c}})}}$, while the red line histograms show the expected signal contribution multiplied by a factor 100. |
png pdf |
Figure 6-b:
The ${m_{\text {SD}}}$ distribution of H in data and simulation in the merged-jet topology analysis signal regions after the maximum likelihood fit, for events in the high purity category. Upper row: 2L channel, electrons (left) and muons (right); middle row: 1L channel, electron (left) and muon (right); lower row: 0L channel. The plain red histograms represent the signal contribution normalized by the post-fit value of $\mu _{{\mathrm{V} \mathrm{H} (\mathrm{H} \to \mathrm{c\bar{c}})}}$, while the red line histograms show the expected signal contribution multiplied by a factor 100. |
png pdf |
Figure 6-c:
The ${m_{\text {SD}}}$ distribution of H in data and simulation in the merged-jet topology analysis signal regions after the maximum likelihood fit, for events in the high purity category. Upper row: 2L channel, electrons (left) and muons (right); middle row: 1L channel, electron (left) and muon (right); lower row: 0L channel. The plain red histograms represent the signal contribution normalized by the post-fit value of $\mu _{{\mathrm{V} \mathrm{H} (\mathrm{H} \to \mathrm{c\bar{c}})}}$, while the red line histograms show the expected signal contribution multiplied by a factor 100. |
png pdf |
Figure 6-d:
The ${m_{\text {SD}}}$ distribution of H in data and simulation in the merged-jet topology analysis signal regions after the maximum likelihood fit, for events in the high purity category. Upper row: 2L channel, electrons (left) and muons (right); middle row: 1L channel, electron (left) and muon (right); lower row: 0L channel. The plain red histograms represent the signal contribution normalized by the post-fit value of $\mu _{{\mathrm{V} \mathrm{H} (\mathrm{H} \to \mathrm{c\bar{c}})}}$, while the red line histograms show the expected signal contribution multiplied by a factor 100. |
png pdf |
Figure 6-e:
The ${m_{\text {SD}}}$ distribution of H in data and simulation in the merged-jet topology analysis signal regions after the maximum likelihood fit, for events in the high purity category. Upper row: 2L channel, electrons (left) and muons (right); middle row: 1L channel, electron (left) and muon (right); lower row: 0L channel. The plain red histograms represent the signal contribution normalized by the post-fit value of $\mu _{{\mathrm{V} \mathrm{H} (\mathrm{H} \to \mathrm{c\bar{c}})}}$, while the red line histograms show the expected signal contribution multiplied by a factor 100. |
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Figure 7:
The fitted signal strength $\mu $ for the ${\mathrm{Z} \mathrm{H} (\mathrm{H} \to \mathrm{c\bar{c}})}$ and ${\mathrm{W} \mathrm{H} (\mathrm{H} \to \mathrm{c\bar{c}})}$ processes, and in each individual channel (0L, 1L, and 2L). The vertical blue line corresponds to the best fit value of $\mu $ for the combination of all channels, while the light-purple band corresponds to the $ \pm $1$\sigma $ uncertainty in the measurement. |
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Figure 8:
The 95% CL upper limits on $\mu $ for the ${\mathrm{V} \mathrm{H} (\mathrm{H} \to \mathrm{c\bar{c}})} $ process from the combination of the resolved-jet and merged-jet topologies analyses in the different channels (0L, 1L, and 2L) and combined. The inner (green) and the outer (yellow) bands indicate the regions containing 68% and 95%, respectively, of the distribution of limits expected under the background-only hypothesis. |
| Tables | |
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Table 1:
Variables employed in the training of the BDT used for each channel of the resolved-jet topology analysis. The 2L case has separate training for the low- and high-$ {{p_{\mathrm {T}}} (\mathrm{V})} $channels, but exploits the same input variables. |
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Table 2:
Variables used in the kinematic BDT training for each channel of the merged-jet topology analysis. |
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Table 3:
Summary of the systematic uncertainties for each channel. Uncertainties in the lepton identification and trigger efficiencies are treated as a normalisation uncertainty in the resolved-jet topology analysis and as a shape uncertainty in the merged-jet topology analysis. |
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Table 4:
Summary of the impact of the statistical and systematic uncertainties on the signal strength modifier for combined analysis of the resolved-jet and merged-jet topologies. |
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Table 5:
Observed and expected UL at 95% CL on the signal strength $\mu $ for the ${\mathrm{V} \mathrm{H} (\mathrm{H} \to \mathrm{c\bar{c}})} $ production for the resolved-jet and merged-jet topologies analyses, which have a significant overlap. The results are also shown separately for each analysis channel. |
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Table 6:
The 95% CL upper limits on the signal strength $\mu _{{\mathrm{V} \mathrm{H} (\mathrm{H} \to \mathrm{c\bar{c}})}}$ for the ${\mathrm{V} \mathrm{H} (\mathrm{H} \to \mathrm{c\bar{c}})} $ process, for the resolved-jet topology analysis for $ {{p_{\mathrm {T}}} (\mathrm{V})} < $ 300 GeV, the merged-jet topology analysis for $ {{p_{\mathrm {T}}} (\mathrm{V})} \geq $ 300 GeV, and their combination. |
| Summary |
|
In this paper, we present the first search by the CMS Collaboration for the standard model (SM) Higgs boson H decaying to a pair of charm quarks, produced in association with a vector boson V (W or Z). The search uses proton-proton collision data at a centre-of-mass energy of 13 TeV collected with the CMS detector in 2016 and corresponding to an integrated luminosity of 35.9 fb$^{-1}$. The search is carried out in five modes, $\mathrm{Z(\mu\mu)H}$, $\mathrm{Z(ee)H}$, $\mathrm{Z(\nu\nu)H}$, $\mathrm{W(\mu\nu)H}$, and ${\mathrm{W}(\mathrm{e}\nu)\mathrm{H}} $, with two complementary analyses targeting different regions of phase space. The signal is extracted by statistically combining the results of the two analyses. Each analysis is first validated by carrying out a search for Z boson decay to a $\mathrm{c\bar{c}}$ pair and comparing the observed signal strength with the SM prediction. The Z boson signal strength for the combination of the two analyses is measured to be $\mu_{{\mathrm{V}\mathrm{Z}(\mathrm{Z}\to \mathrm{c\bar{c}})} }=\sigma/\sigma_\text{SM}=$ 0.55$^{+0.86}_{-0.84}$, with an observed (expected) significance of 0.7 (1.3) standard deviations. The measured best fit value of $\sigma\left({{\mathrm{V}}\mathrm{H}} \right)\mathcal{B}\left(\mathrm{H} \to \mathrm{c\bar{c}} \right)$ for the combination of the two analyses is 2.40$^{+1.12}_{-1.11}$ (stat) $^{+0.65}_{-0.61}$ (syst) pb, which corresponds to a best fit value of $\mu$ for SM $\mathrm{VH(H\to c\bar{c} )}$ production of $\mu_{\mathrm{V}\mathrm{H} cc}=\sigma/\sigma_\text{SM}=$ 37$^{+17}_{-17}$ (stat) $^{+11}_{-9}$ (syst), compatible within two standard deviations with the SM prediction. The larger measured $\mu_{\mathrm{VH(H\to c\bar{c} )}}$ value is due to a small excess observed in data in the resolved analysis, with a local significance of 2.1 standard deviations. The observed (expected) 95% CL upper limit on $\sigma\left({{\mathrm{V}}\mathrm{H}} \right)\mathcal{B}\left(\mathrm{H} \to \mathrm{c\bar{c}} \right)$ from the combination of the two analyses is 4.5 (2.4$^{+1.0}_{-0.7}$) pb. This limit can be translated into an observed (expected) upper limit on $\mu_{\mathrm{VH(H\to c\bar{c} )}}$ of 70 $(37^{+16}_{-11})$ at 95% CL by using the theoretical values of the cross section and branching fraction for the SM H boson with the mass of 125 GeV. This result is the most stringent limit on $\sigma\left({\mathrm{p}}{\mathrm{p}}\to \mathrm{H} \right)\mathcal{B}\left({\mathrm{H}\to\mathrm{c\bar{c}}} \right)$ to-date. |
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