6 The Discovery of the Higgs Boson at the LHC
291
individual Higgs boson production modes are also measured and are shown in Fig.
6.12b. All measurements are consistent with the expectations from the SM.
6.7.3.3 H → WW ( ∗ ) → 2 l 2ν Decay Mode
The H → WW ( ∗ ) decay mode has a large branching fraction (~20%) and a relatively
low-background final state. The study of this final state in which both W bosons
decay leptonically is based on the signature with two isolated, oppositely charged,
high p T leptons (electrons or muons) and large missing transverse momentum,
E T
miss , due to the undetected neutrinos. The signal sensitivity is improved by
separating events according to lepton flavor; into e + e − , μ + μ − , and eμ samples and
according to jet multiplicity into 0-jet and 1-jet samples. The dominant background
arises from irreducible non-resonant WW ( ∗ ) production, and the dominant uncertainties arise from the estimation, using the data themselves, of the backgrounds
from top quark pair, WW ( ∗ ) and DY production.
The final states are categorized according to the number of associated jets, with
the 0-jet category dominating the overall sensitivity. Events are selected that contain
two leptons of either different or the same flavour. The large background from tt
production, the different and same flavour final states are further categorized with 0,
1 and 2 associated jets. In the different-flavour final state, dedicated 2-jet categories
are included to enhance the sensitivity to VBF and VH production mechanisms.
ATLAS has presented measurements of the inclusive cross section of Higgs
boson production via the gluon–gluon fusion (ggF) and vector-boson fusion (VBF)
modes [43], based on an integrated luminosity of 36.1 fb −1 recorded at
√ s = 13 TeV
in 2015–2016. The combined transverse mass distribution for N jet ≤ 1 is shown in
Fig. 6.13a. The ggF and VBF cross-sections times the H → WW ( ∗ ) branching ratio
are measured to be 12.6 ± 1.0(stat) +1.9 –1.8 (syst) pb and 0.50 ± 0.24 (stat) ±0.18
(syst) pb, respectively, in agreement with the SM predictions, as illustrated in Fig.
6.13b.
CMS has published results on the decay mode H → WW ( ∗ ) using data corresponding to an integrated luminosity of 35.9 fb −1 , collected at
√
s = 13 TeV
during 2016 [44]. The expected relative fraction of different Higgs boson production
mechanisms in each category is shown in Fig. 6.14a, together with the expected
signal yield. Combining all channels, the observed cross section times branching
fraction is 1.28 +0.18 –0.17 times the SM prediction for the Higgs boson with a mass
of 125.09 GeV. The ratio of the observed and the predicted cross sections for the
main Higgs boson production modes is shown in Fig. 6.14b. All are consistent with
the predictions from the SM.
6.7.3.4 The H → ττ Decay Mode
All of the decay modes discussed so far test the direct coupling of the Higgs boson to
bosons, and only indirectly probe, through quantum loops, its coupling to fermions.
291
individual Higgs boson production modes are also measured and are shown in Fig.
6.12b. All measurements are consistent with the expectations from the SM.
6.7.3.3 H → WW ( ∗ ) → 2 l 2ν Decay Mode
The H → WW ( ∗ ) decay mode has a large branching fraction (~20%) and a relatively
low-background final state. The study of this final state in which both W bosons
decay leptonically is based on the signature with two isolated, oppositely charged,
high p T leptons (electrons or muons) and large missing transverse momentum,
E T
miss , due to the undetected neutrinos. The signal sensitivity is improved by
separating events according to lepton flavor; into e + e − , μ + μ − , and eμ samples and
according to jet multiplicity into 0-jet and 1-jet samples. The dominant background
arises from irreducible non-resonant WW ( ∗ ) production, and the dominant uncertainties arise from the estimation, using the data themselves, of the backgrounds
from top quark pair, WW ( ∗ ) and DY production.
The final states are categorized according to the number of associated jets, with
the 0-jet category dominating the overall sensitivity. Events are selected that contain
two leptons of either different or the same flavour. The large background from tt
production, the different and same flavour final states are further categorized with 0,
1 and 2 associated jets. In the different-flavour final state, dedicated 2-jet categories
are included to enhance the sensitivity to VBF and VH production mechanisms.
ATLAS has presented measurements of the inclusive cross section of Higgs
boson production via the gluon–gluon fusion (ggF) and vector-boson fusion (VBF)
modes [43], based on an integrated luminosity of 36.1 fb −1 recorded at
√ s = 13 TeV
in 2015–2016. The combined transverse mass distribution for N jet ≤ 1 is shown in
Fig. 6.13a. The ggF and VBF cross-sections times the H → WW ( ∗ ) branching ratio
are measured to be 12.6 ± 1.0(stat) +1.9 –1.8 (syst) pb and 0.50 ± 0.24 (stat) ±0.18
(syst) pb, respectively, in agreement with the SM predictions, as illustrated in Fig.
6.13b.
CMS has published results on the decay mode H → WW ( ∗ ) using data corresponding to an integrated luminosity of 35.9 fb −1 , collected at
√
s = 13 TeV
during 2016 [44]. The expected relative fraction of different Higgs boson production
mechanisms in each category is shown in Fig. 6.14a, together with the expected
signal yield. Combining all channels, the observed cross section times branching
fraction is 1.28 +0.18 –0.17 times the SM prediction for the Higgs boson with a mass
of 125.09 GeV. The ratio of the observed and the predicted cross sections for the
main Higgs boson production modes is shown in Fig. 6.14b. All are consistent with
the predictions from the SM.
6.7.3.4 The H → ττ Decay Mode
All of the decay modes discussed so far test the direct coupling of the Higgs boson to
bosons, and only indirectly probe, through quantum loops, its coupling to fermions.