Search for resonant pair production of Higgs bosons in the $b\bar{b}b\bar{b}$ final state using $pp$ collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector

The collaboration
Phys.Rev.D 105 (2022) 092002, 2022.

Abstract (data abstract)
A search for resonant Higgs boson pair production in the $b\bar{b}b\bar{b}$ final state is presented. The analysis uses 126-139 fb$^{-1}$ of $pp$ collision data at $\sqrt{s}$ = 13 TeV collected with the ATLAS detector at the Large Hadron Collider. The analysis is divided into two channels, targeting Higgs boson decays which are reconstructed as pairs of small-radius jets or as individual large-radius jets. Spin-0 and spin-2 benchmark signal models are considered, both of which correspond to resonant $HH$ production via gluon-gluon fusion. The data are consistent with Standard Model predictions. Upper limits are set on the production cross-section times branching ratio to Higgs boson pairs of a new resonance in the mass range from 251 GeV to 5 TeV. The resolved channel selects four anti-$k_T$ with R = 0.4 central jets ($p_T > 40$ GeV, $|\eta| < 2.5$ and passing a pile-up supression cut). The signal region is defined by four central jets consistent with jets from b-quarks (b-jets) according to the DL1r b-tagging algorithm; these jets are paired into two Higgs candidates and these Higgs candidates masses are required to be consistent with the Higgs boson mass. Additional kinematic cuts are applied to reduce multijets and $t\bar{t}$ backgrounds. A similar selection is performed for the $2b$ region, but requiring two central jets to be b-tagged; this region is used for the data-driven background modeling. The boosted channel requires events to fail the resolved selection. Then, it requires two anti-$k_T$ with R = 1.0 jets ($p_T > 250$ GeV and $|\eta| < 2.0$). Events are classified according to how many variable-radius track jets are reconstructed within these large-R jets, and how many of those track jets are b-tagged with the DL1r algorithm. Signal, validation and control regions are defined according to how consistent the large-R jets masses are with respect to the Higgs boson mass.

• #### Table 1

Data from figure 3a.

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Cumulative acceptance times efficiency as a function of resonance mass for each event selection step in the resolved channel for...

• #### Table 2

Data from figure 3b.

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Cumulative acceptance times efficiency as a function of resonance mass for each event selection step in the resolved channel for...

• #### Table 3

Data from figure 5.

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Corrected $m(HH)$ distribution in the resolved $4b$ validation region (dots), compared with the reweighted distribution in $2b$ validation region (teal...

• #### Table 4

Data from figure 6.

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Corrected $m(HH)$ distribution in the resolved $4b$ signal region (dots), after the fit under the background-only hypothesis. The error bars...

• #### Table 5

Data from auxiliary material figure 2.

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Corrected $m(HH)$ distribution in the resolved $4b$ signal region (dots), after the fit under the background-only hypothesis. The error bars...

• #### Table 6

Data from figure 9a.

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Cumulative signal acceptance times efficiency as a function of the resonance mass for various selection steps in the boosted channel....

• #### Table 7

Data from figure 9b.

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Cumulative signal acceptance times efficiency as a function of the resonance mass for various selection steps in the boosted channel....

• #### Table 8

Data from figure 9c.

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Cumulative signal acceptance times efficiency as a function of the resonance mass for various selection steps in the boosted channel....

• #### Table 9

Data from figure 9d.

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Cumulative signal acceptance times efficiency as a function of the resonance mass for various selection steps in the boosted channel....

• #### Table 10

Data from figure 12a.

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Comparison of the background model (stacked histograms) with data (dots) in the $2b$ validation region. The error bars on the...

• #### Table 11

Data from figure 12b.

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Comparison of the background model (stacked histograms) with data (dots) in the $3b$ validation region. The error bars on the...

• #### Table 12

Data from figure 12c.

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Comparison of the background model (stacked histograms) with data (dots) in the $4b$ validation region. The error bars on the...

• #### Table 13

Data from figure 13a.

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The $m(HH)$ distributions in the boosted $2b$ signal regions (dots), after the fit under the background-only hypothesis. The error bars...

• #### Table 14

Data from auxiliary material figure 5a.

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The $m(HH)$ distributions in the boosted $2b$ signal regions (dots), after the fit under the background-only hypothesis. The error bars...

• #### Table 15

Data from figure 13b.

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The $m(HH)$ distributions in the boosted $3b$ signal regions (dots), after the fit under the background-only hypothesis. The error bars...

• #### Table 16

Data from auxiliary material figure 5b.

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The $m(HH)$ distributions in the boosted $3b$ signal regions (dots), after the fit under the background-only hypothesis. The error bars...

• #### Table 17

Data from figure 13c.

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The $m(HH)$ distributions in the boosted $4b$ signal regions (dots), after the fit under the background-only hypothesis. The error bars...

• #### Table 18

Data from auxiliary material figure 5c.

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The $m(HH)$ distributions in the boosted $4b$ signal regions (dots), after the fit under the background-only hypothesis. The error bars...

• #### Table 19

Data from figure 14a.

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Expected (dashed black lines) and observed (solid black lines) 95% CL upper limits on the cross-section of resonant $HH$ production...

• #### Table 20

Data from figure 14b.

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Expected (dashed black lines) and observed (solid black lines) 95% CL upper limits on the cross-section of resonant $HH$ production...

Version 2 modifications: High-resolution figures were added but otherwise all tables remain unchanged.