Evidence for the H->bb decay with the ATLAS detector

Evidence for the $H \rightarrow b\bar{b}$ decay with the ATLAS detector

ATLAS-CONF-2017-041

6 July 2017

These preliminary results are superseded by the following paper:

HIGG-2016-29
ATLAS recommends to use the results from the paper.

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Abstract

A search for the decay of the Standard Model Higgs boson into a $b\bar{b}$ pair when produced in association with a $W$ or $Z$ boson is performed with the ATLAS detector. The analysed data, corresponding to an integrated luminosity of 36.1 \fb, were collected in proton-proton collisions in Run 2 of the Large Hadron Collider at a centre-of-mass energy of 13 TeV. Final states containing 0, 1 and 2 charged leptons (electrons or muons) are considered, targeting the decays $Z \to \nu\nu$, $W \to \ell\nu$ and $Z \to \ell\ell$. For a Higgs boson mass of 125 GeV, an excess of events over the expected background from other Standard Model processes is found with an observed significance of 3.5 standard deviations, compared to an expectation of 3.0 standard deviations. This excess provides evidence for the Higgs boson decay to $b$-quarks and for its production in association with a vector boson. The ratio $\mu$ of the measured signal strength to the Standard Model expectation is found to be $\mu = 1.20 ^{+0.24}_{-0.23} \mathrm{(stat.)} ^{+0.34}_{-0.28} \mathrm{(syst.)}$. The combination of this result with that of the Run 1 analysis yields $\mu = 0.90 \pm 0.18 \mathrm{(stat.)} ^{+0.21}_{-0.19} \mathrm{(syst.)}$. Assuming the Standard Model production strength, the results are consistent with the value of the Yukawa coupling to $b$-quarks in the Standard Model.

Figures

Figure 1:
Comparison of the m_bb distributions after different stages of jet energy scale and additional corrections, shown for simulated events in the 2-lepton channel in the 2-jet and p_T^Z >150 GeV region. A fit to a Bukin function is superimposed to each distribution, and the resolution values and improvements are reported in the legend.

png (496kB), pdf (392kB)

Figure 2a:
The post-fit distributions for E_T^miss (top left), m_T^W (middle left), m_ℓℓ (bottom left) and m_bb (right) in the 0-lepton (top), 1-lepton (middle) and 2-lepton (bottom) channels for 2-jet, 2 b-tag events in the high p_T^V region. The background contributions after the global likelihood fit are shown as filled histograms. The Higgs boson signal (m_H = 125 GeV) is shown as a filled histogram on top of the fitted backgrounds normalised to the signal yield extracted from data (μ=1.20). The entries in overflow are included in the last bin. The dashed histogram shows the total background as expected from the pre-fit MC simulation. The size of the combined statistical and systematic uncertainty for the sum of the fitted signal and background is indicated by the hatched band. The ratio of the data to the sum of the fitted signal and background is shown in the lower panel.

png (102kB), pdf (21kB)

Figure 2b:
The post-fit distributions for E_T^miss (top left), m_T^W (middle left), m_ℓℓ (bottom left) and m_bb (right) in the 0-lepton (top), 1-lepton (middle) and 2-lepton (bottom) channels for 2-jet, 2 b-tag events in the high p_T^V region. The background contributions after the global likelihood fit are shown as filled histograms. The Higgs boson signal (m_H = 125 GeV) is shown as a filled histogram on top of the fitted backgrounds normalised to the signal yield extracted from data (μ=1.20). The entries in overflow are included in the last bin. The dashed histogram shows the total background as expected from the pre-fit MC simulation. The size of the combined statistical and systematic uncertainty for the sum of the fitted signal and background is indicated by the hatched band. The ratio of the data to the sum of the fitted signal and background is shown in the lower panel.

png (112kB), pdf (24kB)

Figure 2c:
The post-fit distributions for E_T^miss (top left), m_T^W (middle left), m_ℓℓ (bottom left) and m_bb (right) in the 0-lepton (top), 1-lepton (middle) and 2-lepton (bottom) channels for 2-jet, 2 b-tag events in the high p_T^V region. The background contributions after the global likelihood fit are shown as filled histograms. The Higgs boson signal (m_H = 125 GeV) is shown as a filled histogram on top of the fitted backgrounds normalised to the signal yield extracted from data (μ=1.20). The entries in overflow are included in the last bin. The dashed histogram shows the total background as expected from the pre-fit MC simulation. The size of the combined statistical and systematic uncertainty for the sum of the fitted signal and background is indicated by the hatched band. The ratio of the data to the sum of the fitted signal and background is shown in the lower panel.

png (98kB), pdf (20kB)

Figure 2d:
The post-fit distributions for E_T^miss (top left), m_T^W (middle left), m_ℓℓ (bottom left) and m_bb (right) in the 0-lepton (top), 1-lepton (middle) and 2-lepton (bottom) channels for 2-jet, 2 b-tag events in the high p_T^V region. The background contributions after the global likelihood fit are shown as filled histograms. The Higgs boson signal (m_H = 125 GeV) is shown as a filled histogram on top of the fitted backgrounds normalised to the signal yield extracted from data (μ=1.20). The entries in overflow are included in the last bin. The dashed histogram shows the total background as expected from the pre-fit MC simulation. The size of the combined statistical and systematic uncertainty for the sum of the fitted signal and background is indicated by the hatched band. The ratio of the data to the sum of the fitted signal and background is shown in the lower panel.

png (120kB), pdf (25kB)

Figure 2e:
The post-fit distributions for E_T^miss (top left), m_T^W (middle left), m_ℓℓ (bottom left) and m_bb (right) in the 0-lepton (top), 1-lepton (middle) and 2-lepton (bottom) channels for 2-jet, 2 b-tag events in the high p_T^V region. The background contributions after the global likelihood fit are shown as filled histograms. The Higgs boson signal (m_H = 125 GeV) is shown as a filled histogram on top of the fitted backgrounds normalised to the signal yield extracted from data (μ=1.20). The entries in overflow are included in the last bin. The dashed histogram shows the total background as expected from the pre-fit MC simulation. The size of the combined statistical and systematic uncertainty for the sum of the fitted signal and background is indicated by the hatched band. The ratio of the data to the sum of the fitted signal and background is shown in the lower panel.

png (90kB), pdf (20kB)

Figure 2f:
The post-fit distributions for E_T^miss (top left), m_T^W (middle left), m_ℓℓ (bottom left) and m_bb (right) in the 0-lepton (top), 1-lepton (middle) and 2-lepton (bottom) channels for 2-jet, 2 b-tag events in the high p_T^V region. The background contributions after the global likelihood fit are shown as filled histograms. The Higgs boson signal (m_H = 125 GeV) is shown as a filled histogram on top of the fitted backgrounds normalised to the signal yield extracted from data (μ=1.20). The entries in overflow are included in the last bin. The dashed histogram shows the total background as expected from the pre-fit MC simulation. The size of the combined statistical and systematic uncertainty for the sum of the fitted signal and background is indicated by the hatched band. The ratio of the data to the sum of the fitted signal and background is shown in the lower panel.

png (110kB), pdf (23kB)

Figure 3a:
The BDT_VH output post-fit distributions in the 0-lepton (top), 1-lepton (middle) and 2-lepton (bottom) channel for 2-tag events, in the 2-jet (left) and exactly 3 or (≥ 3-jets for the 2-lepton case) (right) categories in the high p_T^V region. The background contributions after the global likelihood fit are shown as filled histograms. The Higgs boson signal (m_H = 125 GeV) is shown as a filled histogram on top of the fitted backgrounds normalised to the signal yield extracted from data (μ=1.20). The dashed histogram shows the total background as expected from the pre-fit MC simulation. The size of the combined statistical and systematic uncertainty for the sum of the fitted signal and background is indicated by the hatched band. The ratio of the data to the sum of the fitted signal and background is shown in the lower panel.

png (99kB), pdf (21kB)

Figure 3b:
The BDT_VH output post-fit distributions in the 0-lepton (top), 1-lepton (middle) and 2-lepton (bottom) channel for 2-tag events, in the 2-jet (left) and exactly 3 or (≥ 3-jets for the 2-lepton case) (right) categories in the high p_T^V region. The background contributions after the global likelihood fit are shown as filled histograms. The Higgs boson signal (m_H = 125 GeV) is shown as a filled histogram on top of the fitted backgrounds normalised to the signal yield extracted from data (μ=1.20). The dashed histogram shows the total background as expected from the pre-fit MC simulation. The size of the combined statistical and systematic uncertainty for the sum of the fitted signal and background is indicated by the hatched band. The ratio of the data to the sum of the fitted signal and background is shown in the lower panel.

png (97kB), pdf (21kB)

Figure 3c:
The BDT_VH output post-fit distributions in the 0-lepton (top), 1-lepton (middle) and 2-lepton (bottom) channel for 2-tag events, in the 2-jet (left) and exactly 3 or (≥ 3-jets for the 2-lepton case) (right) categories in the high p_T^V region. The background contributions after the global likelihood fit are shown as filled histograms. The Higgs boson signal (m_H = 125 GeV) is shown as a filled histogram on top of the fitted backgrounds normalised to the signal yield extracted from data (μ=1.20). The dashed histogram shows the total background as expected from the pre-fit MC simulation. The size of the combined statistical and systematic uncertainty for the sum of the fitted signal and background is indicated by the hatched band. The ratio of the data to the sum of the fitted signal and background is shown in the lower panel.

png (99kB), pdf (22kB)

Figure 3d:
The BDT_VH output post-fit distributions in the 0-lepton (top), 1-lepton (middle) and 2-lepton (bottom) channel for 2-tag events, in the 2-jet (left) and exactly 3 or (≥ 3-jets for the 2-lepton case) (right) categories in the high p_T^V region. The background contributions after the global likelihood fit are shown as filled histograms. The Higgs boson signal (m_H = 125 GeV) is shown as a filled histogram on top of the fitted backgrounds normalised to the signal yield extracted from data (μ=1.20). The dashed histogram shows the total background as expected from the pre-fit MC simulation. The size of the combined statistical and systematic uncertainty for the sum of the fitted signal and background is indicated by the hatched band. The ratio of the data to the sum of the fitted signal and background is shown in the lower panel.

png (96kB), pdf (21kB)

Figure 3e:
The BDT_VH output post-fit distributions in the 0-lepton (top), 1-lepton (middle) and 2-lepton (bottom) channel for 2-tag events, in the 2-jet (left) and exactly 3 or (≥ 3-jets for the 2-lepton case) (right) categories in the high p_T^V region. The background contributions after the global likelihood fit are shown as filled histograms. The Higgs boson signal (m_H = 125 GeV) is shown as a filled histogram on top of the fitted backgrounds normalised to the signal yield extracted from data (μ=1.20). The dashed histogram shows the total background as expected from the pre-fit MC simulation. The size of the combined statistical and systematic uncertainty for the sum of the fitted signal and background is indicated by the hatched band. The ratio of the data to the sum of the fitted signal and background is shown in the lower panel.

png (97kB), pdf (21kB)

Figure 3f:
The BDT_VH output post-fit distributions in the 0-lepton (top), 1-lepton (middle) and 2-lepton (bottom) channel for 2-tag events, in the 2-jet (left) and exactly 3 or (≥ 3-jets for the 2-lepton case) (right) categories in the high p_T^V region. The background contributions after the global likelihood fit are shown as filled histograms. The Higgs boson signal (m_H = 125 GeV) is shown as a filled histogram on top of the fitted backgrounds normalised to the signal yield extracted from data (μ=1.20). The dashed histogram shows the total background as expected from the pre-fit MC simulation. The size of the combined statistical and systematic uncertainty for the sum of the fitted signal and background is indicated by the hatched band. The ratio of the data to the sum of the fitted signal and background is shown in the lower panel.

png (95kB), pdf (21kB)

Figure 4:
The fitted values of the Higgs boson signal strength parameter μ for m_H=125 GeV for the 0-, 1- and 2-lepton channels and their combination. The individual μ values for the lepton channels are obtained from a simultaneous fit with the signal strength parameter for each of the lepton channels floating independently.

png (45kB), pdf (14kB)

Figure 5:
The fitted values of the Higgs boson signal strength parameter μ for m_H=125 GeV for the WH and ZH processes and their combination. The individual μ values for the (W/Z)H processes are obtained from a simultaneous fit with the signal strength for each of the WH and ZH processes floating independently.

png (39kB), pdf (14kB)

Figure 6:
Event yields as a function of log(S/B) for data, background and a Higgs boson signal with m_H=125 GeV. Final-discriminant bins in all signal regions are combined into bins of log(S/B), with the fitted signal being S and the fitted background B. The Higgs boson signal contribution is shown after rescaling the SM cross-section according to the value of the signal strength parameter extracted from data (μ=1.20). The pull (residual divided by its uncertainty) of the data with respect to the background-only prediction is also shown with statistical uncertainties only. The full line indicates the pull of the prediction for signal (μ=1.20) and background with respect to the background-only prediction.

png (88kB), pdf (25kB)

Figure 7:
The distribution of m_bb in data after subtraction of all backgrounds except for the diboson processes, as obtained with the dijet-mass analysis. The contributions from all lepton channels, p_T^V intervals and number-of-jets categories are summed weighted by their respective value of the ratio of fitted Higgs boson signal and background. The expected contribution of the associated WH and ZH production of a SM Higgs boson with m_H=125 GeV is shown scaled by the measured combined signal strength (μ = 1.30). The size of the combined statistical and systematic uncertainty for the fitted background is indicated by the hatched band.

png (57kB), pdf (16kB)

Figure 8:
The fitted values of the VZ signal strength parameter μ_VZ for the WZ and ZZ processes and their combination. The individual μ_VZ values for the (W/Z)Z processes are obtained from a simultaneous fit with the signal strength parameters for each of the WZ and ZZ processes floating independently.

png (38kB), pdf (14kB)

Figure 9:
Event yields as a function of log(S/B) for data, background and VZ process. Final-discriminant bins in all signal regions are combined into bins of log(S/B), with the fitted signal being S and the fitted background B. The VZ contribution is shown after rescaling the SM cross-section according to the value of signal strength extracted from data (μ=1.11). The pull (residual divided by its uncertainty) of the data with respect to the background-only prediction is also shown with statistical uncertainties only. The full line indicates the pull of the prediction for signal (μ=1.11) and background with respect to the background-only prediction.

png (84kB), pdf (24kB)

Figure 10:
The fitted values of the Higgs boson signal strength parameter μ for m_H=125 GeV for the WH and ZH processes and their combination with the 7 TeV, 8 TeV and 13 TeV datasets combined. The individual μ values for the (W/Z)H processes are obtained from a simultaneous fit with the signal strength parameters for each of the WH and ZH processes floating independently.

png (42kB), pdf (14kB)

Figure 11:
The fitted values of the Higgs boson signal strength parameter μ for m_H=125 GeV separately for the 7 TeV, 8 TeV and 13 TeV datasets and their combination.

png (47kB), pdf (14kB)

Figure 12:
Event yields as a function of log(S/B) for data, background and Higgs boson signal with m_H=125 GeV, for the 7 TeV, 8 TeV and 13 TeV datasets combined. Final-discriminant bins in all signal regions are combined into bins of log(S/B), with the fitted signal being S and the fitted background B, for the 7 TeV, 8 TeV and 13 TeV datasets combined. The Higgs boson signal contribution is shown after rescaling the SM cross-section according to the value of signal strength extracted from data (μ=0.90). The pull (residual divided by its uncertainty) of the data with respect to the background-only prediction is also shown with statistical uncertainties only. The full line indicates the pull of the prediction for signal (μ=0.90) and background with respect to the background-only prediction.

png (92kB), pdf (35kB)

Figure 13:
The fitted values of the VZ signal strength parameter μ_VZ for the 0-, 1- and 2-lepton channels and the combination of the three channels. The individual μ_VZ values for the lepton channels are obtained from a simultaneous fit with the signal strength for each of the lepton channels floating independently.

png (43kB), pdf (14kB)

Figure 14a:
Distributions input to the global MVA fit. These distributions complete the set shown in Figure 3. Shown are the data (points with error bars) and expectation (histograms). The background contributions after the global fit are shown as filled histograms. The Higgs boson signal (m_H = 125 GeV) is shown as a filled histogram on top of the fitted backgrounds after rescaling the SM cross-section according to the value of signal strength extracted from data (μ = 1.20) and, unstacked as an unfilled histogram, scaled by the factor indicated in the legend. The dashed histogram shows the total background as expected from the pre-fit MC simulation. The entries in overflow are included in the last bin. The size of the combined statistical and systematic uncertainty for the sum of the signal and fitted background is indicated by the hatched band. The ratio of the data to the sum of the signal and fitted background is shown in the lower panel.

png (96kB), pdf (21kB)

Figure 14b:
Distributions input to the global MVA fit. These distributions complete the set shown in Figure 3. Shown are the data (points with error bars) and expectation (histograms). The background contributions after the global fit are shown as filled histograms. The Higgs boson signal (m_H = 125 GeV) is shown as a filled histogram on top of the fitted backgrounds after rescaling the SM cross-section according to the value of signal strength extracted from data (μ = 1.20) and, unstacked as an unfilled histogram, scaled by the factor indicated in the legend. The dashed histogram shows the total background as expected from the pre-fit MC simulation. The entries in overflow are included in the last bin. The size of the combined statistical and systematic uncertainty for the sum of the signal and fitted background is indicated by the hatched band. The ratio of the data to the sum of the signal and fitted background is shown in the lower panel.

png (93kB), pdf (20kB)

Figure 14c:
Distributions input to the global MVA fit. These distributions complete the set shown in Figure 3. Shown are the data (points with error bars) and expectation (histograms). The background contributions after the global fit are shown as filled histograms. The Higgs boson signal (m_H = 125 GeV) is shown as a filled histogram on top of the fitted backgrounds after rescaling the SM cross-section according to the value of signal strength extracted from data (μ = 1.20) and, unstacked as an unfilled histogram, scaled by the factor indicated in the legend. The dashed histogram shows the total background as expected from the pre-fit MC simulation. The entries in overflow are included in the last bin. The size of the combined statistical and systematic uncertainty for the sum of the signal and fitted background is indicated by the hatched band. The ratio of the data to the sum of the signal and fitted background is shown in the lower panel.

png (51kB), pdf (17kB)

Figure 14d:
Distributions input to the global MVA fit. These distributions complete the set shown in Figure 3. Shown are the data (points with error bars) and expectation (histograms). The background contributions after the global fit are shown as filled histograms. The Higgs boson signal (m_H = 125 GeV) is shown as a filled histogram on top of the fitted backgrounds after rescaling the SM cross-section according to the value of signal strength extracted from data (μ = 1.20) and, unstacked as an unfilled histogram, scaled by the factor indicated in the legend. The dashed histogram shows the total background as expected from the pre-fit MC simulation. The entries in overflow are included in the last bin. The size of the combined statistical and systematic uncertainty for the sum of the signal and fitted background is indicated by the hatched band. The ratio of the data to the sum of the signal and fitted background is shown in the lower panel.

png (42kB), pdf (16kB)

Figure 14e:
Distributions input to the global MVA fit. These distributions complete the set shown in Figure 3. Shown are the data (points with error bars) and expectation (histograms). The background contributions after the global fit are shown as filled histograms. The Higgs boson signal (m_H = 125 GeV) is shown as a filled histogram on top of the fitted backgrounds after rescaling the SM cross-section according to the value of signal strength extracted from data (μ = 1.20) and, unstacked as an unfilled histogram, scaled by the factor indicated in the legend. The dashed histogram shows the total background as expected from the pre-fit MC simulation. The entries in overflow are included in the last bin. The size of the combined statistical and systematic uncertainty for the sum of the signal and fitted background is indicated by the hatched band. The ratio of the data to the sum of the signal and fitted background is shown in the lower panel.

png (49kB), pdf (18kB)

Figure 14f:
Distributions input to the global MVA fit. These distributions complete the set shown in Figure 3. Shown are the data (points with error bars) and expectation (histograms). The background contributions after the global fit are shown as filled histograms. The Higgs boson signal (m_H = 125 GeV) is shown as a filled histogram on top of the fitted backgrounds after rescaling the SM cross-section according to the value of signal strength extracted from data (μ = 1.20) and, unstacked as an unfilled histogram, scaled by the factor indicated in the legend. The dashed histogram shows the total background as expected from the pre-fit MC simulation. The entries in overflow are included in the last bin. The size of the combined statistical and systematic uncertainty for the sum of the signal and fitted background is indicated by the hatched band. The ratio of the data to the sum of the signal and fitted background is shown in the lower panel.

png (50kB), pdf (18kB)

Figure 14g:
Distributions input to the global MVA fit. These distributions complete the set shown in Figure 3. Shown are the data (points with error bars) and expectation (histograms). The background contributions after the global fit are shown as filled histograms. The Higgs boson signal (m_H = 125 GeV) is shown as a filled histogram on top of the fitted backgrounds after rescaling the SM cross-section according to the value of signal strength extracted from data (μ = 1.20) and, unstacked as an unfilled histogram, scaled by the factor indicated in the legend. The dashed histogram shows the total background as expected from the pre-fit MC simulation. The entries in overflow are included in the last bin. The size of the combined statistical and systematic uncertainty for the sum of the signal and fitted background is indicated by the hatched band. The ratio of the data to the sum of the signal and fitted background is shown in the lower panel.

png (54kB), pdf (18kB)

Figure 14h:
Distributions input to the global MVA fit. These distributions complete the set shown in Figure 3. Shown are the data (points with error bars) and expectation (histograms). The background contributions after the global fit are shown as filled histograms. The Higgs boson signal (m_H = 125 GeV) is shown as a filled histogram on top of the fitted backgrounds after rescaling the SM cross-section according to the value of signal strength extracted from data (μ = 1.20) and, unstacked as an unfilled histogram, scaled by the factor indicated in the legend. The dashed histogram shows the total background as expected from the pre-fit MC simulation. The entries in overflow are included in the last bin. The size of the combined statistical and systematic uncertainty for the sum of the signal and fitted background is indicated by the hatched band. The ratio of the data to the sum of the signal and fitted background is shown in the lower panel.

png (54kB), pdf (18kB)

Figure 15a:
Distributions input for the signal regions to the global MVA_VZ fit. Shown are the data (points with error bars) and expectation (histograms). The background contributions after the global fit are shown as filled histograms. The VZ signal is shown as a filled histogram on top of the fitted backgrounds after rescaling the SM cross-section according to the value of signal strength extracted from data (μ = 1.11) and, unstacked as an unfilled histogram, scaled by the factor indicated in the legend. The dashed histogram shows the total background as expected from the pre-fit MC simulation. The entries in overflow are included in the last bin. The size of the combined statistical and systematic uncertainty for the sum of the signal and fitted background is indicated by the hatched band. The ratio of the data to the sum of the signal and fitted background is shown in the lower panel.

png (88kB), pdf (20kB)

Figure 15b:
Distributions input for the signal regions to the global MVA_VZ fit. Shown are the data (points with error bars) and expectation (histograms). The background contributions after the global fit are shown as filled histograms. The VZ signal is shown as a filled histogram on top of the fitted backgrounds after rescaling the SM cross-section according to the value of signal strength extracted from data (μ = 1.11) and, unstacked as an unfilled histogram, scaled by the factor indicated in the legend. The dashed histogram shows the total background as expected from the pre-fit MC simulation. The entries in overflow are included in the last bin. The size of the combined statistical and systematic uncertainty for the sum of the signal and fitted background is indicated by the hatched band. The ratio of the data to the sum of the signal and fitted background is shown in the lower panel.

png (86kB), pdf (20kB)

Figure 15c:
Distributions input for the signal regions to the global MVA_VZ fit. Shown are the data (points with error bars) and expectation (histograms). The background contributions after the global fit are shown as filled histograms. The VZ signal is shown as a filled histogram on top of the fitted backgrounds after rescaling the SM cross-section according to the value of signal strength extracted from data (μ = 1.11) and, unstacked as an unfilled histogram, scaled by the factor indicated in the legend. The dashed histogram shows the total background as expected from the pre-fit MC simulation. The entries in overflow are included in the last bin. The size of the combined statistical and systematic uncertainty for the sum of the signal and fitted background is indicated by the hatched band. The ratio of the data to the sum of the signal and fitted background is shown in the lower panel.

png (89kB), pdf (20kB)

Figure 15d:
Distributions input for the signal regions to the global MVA_VZ fit. Shown are the data (points with error bars) and expectation (histograms). The background contributions after the global fit are shown as filled histograms. The VZ signal is shown as a filled histogram on top of the fitted backgrounds after rescaling the SM cross-section according to the value of signal strength extracted from data (μ = 1.11) and, unstacked as an unfilled histogram, scaled by the factor indicated in the legend. The dashed histogram shows the total background as expected from the pre-fit MC simulation. The entries in overflow are included in the last bin. The size of the combined statistical and systematic uncertainty for the sum of the signal and fitted background is indicated by the hatched band. The ratio of the data to the sum of the signal and fitted background is shown in the lower panel.

png (88kB), pdf (20kB)

Figure 15e:
Distributions input for the signal regions to the global MVA_VZ fit. Shown are the data (points with error bars) and expectation (histograms). The background contributions after the global fit are shown as filled histograms. The VZ signal is shown as a filled histogram on top of the fitted backgrounds after rescaling the SM cross-section according to the value of signal strength extracted from data (μ = 1.11) and, unstacked as an unfilled histogram, scaled by the factor indicated in the legend. The dashed histogram shows the total background as expected from the pre-fit MC simulation. The entries in overflow are included in the last bin. The size of the combined statistical and systematic uncertainty for the sum of the signal and fitted background is indicated by the hatched band. The ratio of the data to the sum of the signal and fitted background is shown in the lower panel.

png (87kB), pdf (20kB)

Figure 15f:
Distributions input for the signal regions to the global MVA_VZ fit. Shown are the data (points with error bars) and expectation (histograms). The background contributions after the global fit are shown as filled histograms. The VZ signal is shown as a filled histogram on top of the fitted backgrounds after rescaling the SM cross-section according to the value of signal strength extracted from data (μ = 1.11) and, unstacked as an unfilled histogram, scaled by the factor indicated in the legend. The dashed histogram shows the total background as expected from the pre-fit MC simulation. The entries in overflow are included in the last bin. The size of the combined statistical and systematic uncertainty for the sum of the signal and fitted background is indicated by the hatched band. The ratio of the data to the sum of the signal and fitted background is shown in the lower panel.

png (84kB), pdf (19kB)

Figure 16a:
BDT input variables. (top: 0-lepton) Δ R(b₁,b₂) and m_bbj for 2-jet and 3-jet category respectively. (middle: 1-lepton) min[|Δφ(ℓ,b)|] and m_bb for 2-jet and 3-jet category respectively. (bottom: 2-lepton) E_T^miss and p_T(b₂) for 2-jet category with p_T^Z>150 GeV. The Higgs boson signal (m_H = 125 GeV) is shown as a filled histogram on top of the fitted backgrounds after rescaling the SM cross-section according to the value of signal strength extracted from data (μ = 1.20) and, unstacked as an unfilled histogram, scaled by the factor indicated in the legend. The dashed histogram shows the total background as expected from the pre-fit MC simulation. The entries in overflow are included in the last bin. The combined statistical and systematic uncertainty for the sum of the signal and fitted background is indicated by the hatched band. The ratio of the data to the sum of the signal and fitted background is shown in the lower panel.

png (140kB), pdf (23kB)

Figure 16b:
BDT input variables. (top: 0-lepton) Δ R(b₁,b₂) and m_bbj for 2-jet and 3-jet category respectively. (middle: 1-lepton) min[|Δφ(ℓ,b)|] and m_bb for 2-jet and 3-jet category respectively. (bottom: 2-lepton) E_T^miss and p_T(b₂) for 2-jet category with p_T^Z>150 GeV. The Higgs boson signal (m_H = 125 GeV) is shown as a filled histogram on top of the fitted backgrounds after rescaling the SM cross-section according to the value of signal strength extracted from data (μ = 1.20) and, unstacked as an unfilled histogram, scaled by the factor indicated in the legend. The dashed histogram shows the total background as expected from the pre-fit MC simulation. The entries in overflow are included in the last bin. The combined statistical and systematic uncertainty for the sum of the signal and fitted background is indicated by the hatched band. The ratio of the data to the sum of the signal and fitted background is shown in the lower panel.

png (101kB), pdf (20kB)

Figure 16c:
BDT input variables. (top: 0-lepton) Δ R(b₁,b₂) and m_bbj for 2-jet and 3-jet category respectively. (middle: 1-lepton) min[|Δφ(ℓ,b)|] and m_bb for 2-jet and 3-jet category respectively. (bottom: 2-lepton) E_T^miss and p_T(b₂) for 2-jet category with p_T^Z>150 GeV. The Higgs boson signal (m_H = 125 GeV) is shown as a filled histogram on top of the fitted backgrounds after rescaling the SM cross-section according to the value of signal strength extracted from data (μ = 1.20) and, unstacked as an unfilled histogram, scaled by the factor indicated in the legend. The dashed histogram shows the total background as expected from the pre-fit MC simulation. The entries in overflow are included in the last bin. The combined statistical and systematic uncertainty for the sum of the signal and fitted background is indicated by the hatched band. The ratio of the data to the sum of the signal and fitted background is shown in the lower panel.

png (128kB), pdf (21kB)

Figure 16d:
BDT input variables. (top: 0-lepton) Δ R(b₁,b₂) and m_bbj for 2-jet and 3-jet category respectively. (middle: 1-lepton) min[|Δφ(ℓ,b)|] and m_bb for 2-jet and 3-jet category respectively. (bottom: 2-lepton) E_T^miss and p_T(b₂) for 2-jet category with p_T^Z>150 GeV. The Higgs boson signal (m_H = 125 GeV) is shown as a filled histogram on top of the fitted backgrounds after rescaling the SM cross-section according to the value of signal strength extracted from data (μ = 1.20) and, unstacked as an unfilled histogram, scaled by the factor indicated in the legend. The dashed histogram shows the total background as expected from the pre-fit MC simulation. The entries in overflow are included in the last bin. The combined statistical and systematic uncertainty for the sum of the signal and fitted background is indicated by the hatched band. The ratio of the data to the sum of the signal and fitted background is shown in the lower panel.

png (113kB), pdf (24kB)

Figure 16e:
BDT input variables. (top: 0-lepton) Δ R(b₁,b₂) and m_bbj for 2-jet and 3-jet category respectively. (middle: 1-lepton) min[|Δφ(ℓ,b)|] and m_bb for 2-jet and 3-jet category respectively. (bottom: 2-lepton) E_T^miss and p_T(b₂) for 2-jet category with p_T^Z>150 GeV. The Higgs boson signal (m_H = 125 GeV) is shown as a filled histogram on top of the fitted backgrounds after rescaling the SM cross-section according to the value of signal strength extracted from data (μ = 1.20) and, unstacked as an unfilled histogram, scaled by the factor indicated in the legend. The dashed histogram shows the total background as expected from the pre-fit MC simulation. The entries in overflow are included in the last bin. The combined statistical and systematic uncertainty for the sum of the signal and fitted background is indicated by the hatched band. The ratio of the data to the sum of the signal and fitted background is shown in the lower panel.

png (92kB), pdf (20kB)

Figure 16f:
BDT input variables. (top: 0-lepton) Δ R(b₁,b₂) and m_bbj for 2-jet and 3-jet category respectively. (middle: 1-lepton) min[|Δφ(ℓ,b)|] and m_bb for 2-jet and 3-jet category respectively. (bottom: 2-lepton) E_T^miss and p_T(b₂) for 2-jet category with p_T^Z>150 GeV. The Higgs boson signal (m_H = 125 GeV) is shown as a filled histogram on top of the fitted backgrounds after rescaling the SM cross-section according to the value of signal strength extracted from data (μ = 1.20) and, unstacked as an unfilled histogram, scaled by the factor indicated in the legend. The dashed histogram shows the total background as expected from the pre-fit MC simulation. The entries in overflow are included in the last bin. The combined statistical and systematic uncertainty for the sum of the signal and fitted background is indicated by the hatched band. The ratio of the data to the sum of the signal and fitted background is shown in the lower panel.

png (118kB), pdf (19kB)

Figure 17a:
Distributions of the p_T^V for signal and control regions. The distribution for the 0-lepton 2-jet signal region can be found in Figure 2. Shown are the data (points with error bars) and expectation (histograms). The background contributions after the global fit are shown as filled histograms. The Higgs boson signal (m_H = 125 GeV) is shown as a filled histogram on top of the fitted backgrounds after rescaling the SM cross-section according to the value of signal strength extracted from data (μ = 1.20) and, unstacked as an unfilled histogram, scaled by the factor indicated in the legend. The dashed histogram shows the total background as expected from the pre-fit MC simulation. The entries in overflow are included in the last bin. The size of the combined statistical and systematic uncertainty for the sum of the signal and fitted background is indicated by the hatched band. The ratio of the data to the sum of the signal and fitted background is shown in the lower panel.

png (99kB), pdf (21kB)

Figure 17b:
Distributions of the p_T^V for signal and control regions. The distribution for the 0-lepton 2-jet signal region can be found in Figure 2. Shown are the data (points with error bars) and expectation (histograms). The background contributions after the global fit are shown as filled histograms. The Higgs boson signal (m_H = 125 GeV) is shown as a filled histogram on top of the fitted backgrounds after rescaling the SM cross-section according to the value of signal strength extracted from data (μ = 1.20) and, unstacked as an unfilled histogram, scaled by the factor indicated in the legend. The dashed histogram shows the total background as expected from the pre-fit MC simulation. The entries in overflow are included in the last bin. The size of the combined statistical and systematic uncertainty for the sum of the signal and fitted background is indicated by the hatched band. The ratio of the data to the sum of the signal and fitted background is shown in the lower panel.

png (99kB), pdf (21kB)

Figure 17c:
Distributions of the p_T^V for signal and control regions. The distribution for the 0-lepton 2-jet signal region can be found in Figure 2. Shown are the data (points with error bars) and expectation (histograms). The background contributions after the global fit are shown as filled histograms. The Higgs boson signal (m_H = 125 GeV) is shown as a filled histogram on top of the fitted backgrounds after rescaling the SM cross-section according to the value of signal strength extracted from data (μ = 1.20) and, unstacked as an unfilled histogram, scaled by the factor indicated in the legend. The dashed histogram shows the total background as expected from the pre-fit MC simulation. The entries in overflow are included in the last bin. The size of the combined statistical and systematic uncertainty for the sum of the signal and fitted background is indicated by the hatched band. The ratio of the data to the sum of the signal and fitted background is shown in the lower panel.

png (95kB), pdf (20kB)

Figure 17d:
Distributions of the p_T^V for signal and control regions. The distribution for the 0-lepton 2-jet signal region can be found in Figure 2. Shown are the data (points with error bars) and expectation (histograms). The background contributions after the global fit are shown as filled histograms. The Higgs boson signal (m_H = 125 GeV) is shown as a filled histogram on top of the fitted backgrounds after rescaling the SM cross-section according to the value of signal strength extracted from data (μ = 1.20) and, unstacked as an unfilled histogram, scaled by the factor indicated in the legend. The dashed histogram shows the total background as expected from the pre-fit MC simulation. The entries in overflow are included in the last bin. The size of the combined statistical and systematic uncertainty for the sum of the signal and fitted background is indicated by the hatched band. The ratio of the data to the sum of the signal and fitted background is shown in the lower panel.

png (90kB), pdf (19kB)

Figure 17e:
Distributions of the p_T^V for signal and control regions. The distribution for the 0-lepton 2-jet signal region can be found in Figure 2. Shown are the data (points with error bars) and expectation (histograms). The background contributions after the global fit are shown as filled histograms. The Higgs boson signal (m_H = 125 GeV) is shown as a filled histogram on top of the fitted backgrounds after rescaling the SM cross-section according to the value of signal strength extracted from data (μ = 1.20) and, unstacked as an unfilled histogram, scaled by the factor indicated in the legend. The dashed histogram shows the total background as expected from the pre-fit MC simulation. The entries in overflow are included in the last bin. The size of the combined statistical and systematic uncertainty for the sum of the signal and fitted background is indicated by the hatched band. The ratio of the data to the sum of the signal and fitted background is shown in the lower panel.

png (89kB), pdf (19kB)

Figure 17f:
Distributions of the p_T^V for signal and control regions. The distribution for the 0-lepton 2-jet signal region can be found in Figure 2. Shown are the data (points with error bars) and expectation (histograms). The background contributions after the global fit are shown as filled histograms. The Higgs boson signal (m_H = 125 GeV) is shown as a filled histogram on top of the fitted backgrounds after rescaling the SM cross-section according to the value of signal strength extracted from data (μ = 1.20) and, unstacked as an unfilled histogram, scaled by the factor indicated in the legend. The dashed histogram shows the total background as expected from the pre-fit MC simulation. The entries in overflow are included in the last bin. The size of the combined statistical and systematic uncertainty for the sum of the signal and fitted background is indicated by the hatched band. The ratio of the data to the sum of the signal and fitted background is shown in the lower panel.

png (110kB), pdf (24kB)

Figure 17g:
Distributions of the p_T^V for signal and control regions. The distribution for the 0-lepton 2-jet signal region can be found in Figure 2. Shown are the data (points with error bars) and expectation (histograms). The background contributions after the global fit are shown as filled histograms. The Higgs boson signal (m_H = 125 GeV) is shown as a filled histogram on top of the fitted backgrounds after rescaling the SM cross-section according to the value of signal strength extracted from data (μ = 1.20) and, unstacked as an unfilled histogram, scaled by the factor indicated in the legend. The dashed histogram shows the total background as expected from the pre-fit MC simulation. The entries in overflow are included in the last bin. The size of the combined statistical and systematic uncertainty for the sum of the signal and fitted background is indicated by the hatched band. The ratio of the data to the sum of the signal and fitted background is shown in the lower panel.

png (111kB), pdf (24kB)

Figure 17h:
Distributions of the p_T^V for signal and control regions. The distribution for the 0-lepton 2-jet signal region can be found in Figure 2. Shown are the data (points with error bars) and expectation (histograms). The background contributions after the global fit are shown as filled histograms. The Higgs boson signal (m_H = 125 GeV) is shown as a filled histogram on top of the fitted backgrounds after rescaling the SM cross-section according to the value of signal strength extracted from data (μ = 1.20) and, unstacked as an unfilled histogram, scaled by the factor indicated in the legend. The dashed histogram shows the total background as expected from the pre-fit MC simulation. The entries in overflow are included in the last bin. The size of the combined statistical and systematic uncertainty for the sum of the signal and fitted background is indicated by the hatched band. The ratio of the data to the sum of the signal and fitted background is shown in the lower panel.

png (85kB), pdf (19kB)

Figure 17i:
Distributions of the p_T^V for signal and control regions. The distribution for the 0-lepton 2-jet signal region can be found in Figure 2. Shown are the data (points with error bars) and expectation (histograms). The background contributions after the global fit are shown as filled histograms. The Higgs boson signal (m_H = 125 GeV) is shown as a filled histogram on top of the fitted backgrounds after rescaling the SM cross-section according to the value of signal strength extracted from data (μ = 1.20) and, unstacked as an unfilled histogram, scaled by the factor indicated in the legend. The dashed histogram shows the total background as expected from the pre-fit MC simulation. The entries in overflow are included in the last bin. The size of the combined statistical and systematic uncertainty for the sum of the signal and fitted background is indicated by the hatched band. The ratio of the data to the sum of the signal and fitted background is shown in the lower panel.

png (93kB), pdf (20kB)

Figure 18:
A 2 b-tag, 2-jet, 1-electron event within the most signal-like portion of the BDT_VH output distribution is shown (Run 303499, Event 2810362531). The electron is shown as a red track with a large energy deposit in the electromagnetic calorimeter, corresponding to light green bars, and has a p_T of 151 GeV. The E_T^miss, shown as a white dashed line, has a magnitude of 320 GeV. These correspond to a p_T^V of 450 GeV. The two central high-p_T b-tagged jets are represented by light yellow cones. They contain the green and yellow bars corresponding to the energy deposition in the electromagnetic and hadronic calorimeters respectively, and they have an invariant mass of 124 GeV.

png (777kB),

Figure 19:
A 2 b-tag, 2-jet, 2-muon event within the most signal-like portion of the BDT_VH output distribution is shown (Run 309440, Event 990753168). The event stems from the high p_T^V analysis region. Muons are shown as red tracks. Two of them form an invariant mass of 88.7 GeV, compatible with a Z boson, while a third one is found within Δ R of 0.4 of a jet and utilised in the muon-in-jet correction. The two central high-p_T b-tagged jets are represented by light yellow cones. They contain the green and yellow bars corresponding to the energy deposition in the electromagnetic and hadronic calorimeters respectively, and they have an invariant mass of 123.3 GeV. The value of p_T^V is 204 GeV.

png (755kB),

Tables

Table 1:
The generators used for the simulation of the signal and background processes. If not specified, the order of the cross-section calculation refers to the QCD expansion. The acronyms ME, PS and UE are used for matrix element, parton shower and underlying event, respectively. (*) The events are generated using the first PDF in the set NNPDF3.0NLO and subsequentially reweighted to PDF4LHC15NLO using the internal algorithm in Powheg-Box v2. (†) The NNLO(QCD)+NLO(EW) cross-section calculation for the pp → ZH process already includes the gg→ ZH contribution. The qq→ ZH process is normalised to the NNLO(QCD)+NLO(EW) cross-section for the pp → ZH process, after subtracting the gg→ ZH contribution.

png (65kB), pdf (70kB)

Table 2:
Summary of the event selection in the 0-, 1- and 2-lepton channels.

png (62kB), pdf (69kB)

Table 3:
The cross-section times branching ratio (BR) and acceptance for the three channels at 13 TeV. The qq- and gg-initiated ZH processes are shown separately. The branching ratios are calculated considering only decays to muons and electrons for Z→ℓℓ, decays to all three lepton flavours for W→ℓν and decays to neutrinos for Z→νν. The acceptance is calculated as the fraction of events remaining in the combined signal and control regions after the full event selection.

png (21kB), pdf (42kB)

Table 4:
Summary of the event selection criteria in the 0-, 1- and 2-lepton channels for the dijet-mass analysis, applied in addition to those described in Table 2 for the multivariate analysis.

png (16kB), pdf (48kB)

Table 5:
Variables used for the multivariate discriminant in each of the categories.

png (19kB), pdf (57kB)

Table 6:
Summary of the systematic uncertainties in the background modelling for Z+jets, W+jets, tt, single top-quark and multi-jet production. An 'S' symbol is used when only a shape uncertainty is assessed. The regions in which the normalisations are floated independently are listed in brackets.

png (69kB), pdf (43kB)

Table 7:
Summary of the systematic uncertainties in the background modelling for diboson production. 'PS/UE' indicates parton shower/underlying event. An 'S' symbol is used when only a shape uncertainty is assessed. When determining the (W/Z)Z diboson production signal strength, the normalisation uncertainties in ZZ and WZ production are removed.

png (56kB), pdf (41kB)

Table 8:
Summary of the systematic uncertainties in the signal modelling. 'PS/UE' indicates parton shower / underlying event. An 'S' symbol is used when only a shape uncertainty is assessed.

png (35kB), pdf (50kB)

Table 9:
The distributions used in the global likelihood fit for the signal regions (SR) and control regions (CR) for all the categories in each channel, for the nominal multivariate analysis.

png (20kB), pdf (40kB)

Table 10:
Factors applied to the nominal normalisations of the tt, W+HF and Z+HF backgrounds, as obtained from the global fit to the 13 TeV data for the nominal multivariate analysis, used to extract the Higgs boson signal. The errors include the statistical and systematic uncertainties.

png (10kB), pdf (31kB)

Table 11:
Breakdown of the contributions to the uncertainties in μ. The sum in quadrature of the systematic uncertainties attached to the categories differs from the total systematic uncertainty due to correlations.

png (27kB), pdf (42kB)

Table 12:
Regions used in likelihood fit for the di-jet mass analysis

png (24kB), pdf (48kB)

Table 13:
The fitted Higgs boson signal and background yields for each signal region category in each channel after the full selection of the multivariate analysis. The yields are normalised by the results of the global likelihood fit. All systematic uncertainties are included in the indicated uncertainties. An entry of "-" indicates that a specific background component is missing in a certain region, or that no simulated events are left after the analysis selection.

png (77kB), pdf (51kB)

Table 14:
The expected and observed p₀ and significance values for the individual lepton channels and their combination using the 13 TeV dataset. The expected values are evaluated assuming a SM Higgs boson with a mass of 125 GeV.

png (10kB), pdf (31kB)

Table 15:
The numbers of fitted signal and background events and the observed numbers of events in the bins of Figure 6. An entry of "-" indicates that a specific background component is missing in a certain bin, or that no simulated events are left after the analysis selection.

png (25kB), pdf (28kB)

Table 16:
The fitted signal and background yields for each control region category in each channel, corresponding to the selection applied to the control regions for the multivariate analysis. The yields are normalised by the results of the global likelihood fit. All systematic uncertainties are included in the indicated uncertainties. An entry of "-" indicates that a specific background component is missing in a certain region, or that no simulated events are left after the analysis selection.

png (50kB), pdf (51kB)

© 2017 CERN for the benefit of the ATLAS Collaboration. Reproduction of the article, figures and tables on this page is allowed as specified in the CC-BY-4.0 license.
2019-09-13 00:20:19