Study of High-Transverse-Momentum Higgs Boson Production in Association with a Vector Boson in the $qqbb$ Final State with the ATLAS Detector

This Letter presents the first study of Higgs boson production in association with a vector boson ($V=W$ or $Z$) in the fully hadronic $qqbb$ final state using data recorded by the ATLAS detector at the LHC in proton-proton collisions at $\sqrt{s}=13\mathrm{TeV}$ and corresponding to an integrated luminosity of $137{\mathrm{fb}}^{-1}$. The vector bosons and Higgs bosons are each reconstructed as large-radius jets and tagged using jet substructure techniques. Dedicated tagging algorithms exploiting $b$-tagging properties are used to identify jets consistent with Higgs bosons decaying into $b\overline{b}$. Dominant backgrounds from multijet production are determined directly from the data, and a likelihood fit to the jet mass distribution of Higgs boson candidates is used to extract the number of signal events. The $VH$ production cross section is measured inclusively and differentially in several ranges of Higgs boson transverse momentum: 250–450, 450–650, and greater than 650 GeV. The inclusive signal yield relative to the standard model expectation is observed to be $\mu ={1.4}_{-0.9}^{+1.0}$ and the corresponding cross section is $3.1\pm 1.3(\mathrm{stat}{)}_{-1.4}^{+1.8}(\mathrm{syst})\mathrm{pb}$.

Figure 1

Higgs candidate jet mass distributions in the signal region for $p_{\mathrm{T},\mathrm{J}}^H\in [250,450)\mathrm{GeV}$ (left), $p_{\mathrm{T},\mathrm{J}}^H\in [450,650)\mathrm{GeV}$ (middle), and $p_{\mathrm{T},\mathrm{J}}^H\ge 650\mathrm{GeV}$ (right) obtained after the inclusive fit with a single $Z+\text{jets}$ normalization factor and a single signal strength. The bottom panels show the distributions after subtracting the multijet and top-quark backgrounds. The hatched bands show the total uncertainty in the background estimate.

Figure 2

Higgs candidate jet mass distributions for the multijet background in the signal region estimated with either the nominal transfer factor method (TF) or the boosted decision tree method (BDT). The error bars (hatched uncertainty band) represent(s) the total uncertainty in the TF (BDT) estimate including both the statistical and systematic uncertainties. The BDT uncertainties comprise a statistical component obtained using the method from Ref. [60] and the difference between the data and the background estimate in the validation regions. This difference is relatively large in the last $p_{\mathrm{T}}$ bin. It should be noted that there is a strong statistical correlation between the distributions from the two methods and that the BDT uncertainties are small in the first two $p_{\mathrm{T}}$ bins.

Figure 3

Higgs candidate jet mass distributions after the inclusive fit in the validation region consisting of events passing the 80% efficiency working point of the $V$-jet tagger but failing only the $D_2^{\beta =1}$ requirement of its tighter 50% efficiency working point. No $H\to b\overline{b}$ tagging is applied. The bottom panels show the distributions after subtracting the multijet and top-quark backgrounds. The hatched bands show the total uncertainty in the background estimate.