Abstract
Measurements of the Standard Model Higgs boson decaying into a bbar{b} pair and produced in association with a W or Z boson decaying into leptons, using proton–proton collision data collected between 2015 and 2018 by the ATLAS detector, are presented. The measurements use collisions produced by the Large Hadron Collider at a centre-of-mass energy of sqrt{s} = 13,text {Te}text {V}, corresponding to an integrated luminosity of 139,mathrm {fb}^{-1}. The production of a Higgs boson in association with a W or Z boson is established with observed (expected) significances of 4.0 (4.1) and 5.3 (5.1) standard deviations, respectively. Cross-sections of associated production of a Higgs boson decaying into bottom quark pairs with an electroweak gauge boson, W or Z, decaying into leptons are measured as a function of the gauge boson transverse momentum in kinematic fiducial volumes. The cross-section measurements are all consistent with the Standard Model expectations, and the total uncertainties vary from 30% in the high gauge boson transverse momentum regions to 85% in the low regions. Limits are subsequently set on the parameters of an effective Lagrangian sensitive to modifications of the WH and ZH processes as well as the Higgs boson decay into bbar{b}.
Highlights
Background modellingThe simulated event samples summarised in Sect. 3 are used to model all background processes, except for the ttbackground in the 2-lepton channel6 and the multi-jet background in the 1-lepton channel, which are both estimated using datadriven techniques, as discussed below.6.1 Data-driven ttbackground estimationIn the 2-lepton channel a high-purity control region, over 99% pure in ttand single-top-quark W t events, is defined using the nominal event selection, but replacing the same-flavour lepton selection with a requirement of exactly one electron and one muon
The post-fit normalisation factors of the unconstrained backgrounds in the global likelihood fit are shown for the singlePOI multivariate analysis in Table 9, the post-fit signal and background yields are shown in Tables 10 and 11, and Fig. 3 shows the BDTV H output distributions in the high- pTV 2-jet signal region (SR), which are most sensitive to the signal
The impact of a set of systematic uncertainties is defined as the difference in quadrature between the uncertainty in μ computed when all nuisance parameters (NP) are fitted and that when the NPs in the set are fixed to their best-fit values
Summary
ATLAS [37] is a general-purpose particle detector covering nearly the entire solid angle around the collision point. An inner tracking detector, located within a 2 T axial magnetic field generated by a thin superconducting solenoid, is used to measure the trajectories and momenta of charged particles. The inner layers consist of high-granularity silicon pixel detectors covering a pseudorapidity range |η| < 2.5, with an innermost layer [38,39] that was added to the detector between Run 1 and Run 2. The first level is a hardware implementation aiming to reduce the rate to around 100 kHz, while the software-based high-level trigger provides the remaining rate reduction to approximately 1 kHz. all samples of simulated events, except for those generated using Sherpa [48], the EvtGen v1.6.0 program [49] was used to describe the decays of bottom and charm hadrons
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