Search for dark matter produced in association with a Standard Model Higgs boson decaying into b-quarks using the full Run 2 dataset from the ATLAS detector

Abstract

The production of dark matter in association with Higgs bosons is predicted in several extensions of the Standard Model. An exploration of such scenarios is presented, considering final states with missing transverse momentum and b-tagged jets consistent with a Higgs boson. The analysis uses proton-proton collision data at a centre-of-mass energy of 13 TeV recorded by the ATLAS experiment at the LHC during Run 2, amounting to an integrated luminosity of 139 fb−1. The analysis, when compared with previous searches, benefits from a larger dataset, but also has further improvements providing sensitivity to a wider spectrum of signal scenarios. These improvements include both an optimised event selection and advances in the object identification, such as the use of the likelihood-based significance of the missing transverse momentum and variable-radius track-jets. No significant deviation from Standard Model expectations is observed. Limits are set, at 95% confidence level, in two benchmark models with two Higgs doublets extended by either a heavy vector boson Z′ or a pseudoscalar singlet a and which both provide a dark matter candidate χ. In the case of the two-Higgs-doublet model with an additional vector boson Z′, the observed limits extend up to a Z′ mass of 3 TeV for a mass of 100 GeV for the dark matter candidate. The two-Higgs-doublet model with a dark matter particle mass of 10 GeV and an additional pseudoscalar a is excluded for masses of the a up to 520 GeV and 240 GeV for tan β = 1 and tan β = 10 respectively. Limits on the visible cross-sections are set and range from to 0.05 fb to 3.26 fb, depending on the missing transverse momentum and b-quark jet multiplicity requirements.

Benchmarking LHC searches for light 2HDM+$\boldsymbol{a}$ pseudoscalars

“…Since for models with pseudoscalar mediators the DM direct detection (DD) constraints are weaker compared to models with scalar mediators, such models are more attractive from an astrophysical point of view since they often allow to reproduce the observed DM relic abundance in a wider parameter space and with less tuning. These features admit a host of missing transverse momentum (E miss T ) signatures at colliders which can be consistently compared and combined, making the 2HDM+a model one of the pillars of the LHC DM search programme [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22].…”

“…The parameter region shaded purple is excluded by the dimuon searches in radiative Υ-mesons decays [55,56]. The blue contour is the exclusion that derives from the latest searches for h → inv [50,51], while the constraint that derives from a recast of the h + E miss T analysis in the h → b b channel [18] is shown in green. The black dotted contours indicate the parameter choices for which the correct DM relic density Ω χ h 2 = 0.12 [57] is achieved.…”

“…The corresponding 95% CL exclusions are shown in blue and green in the right panel of Figure 1, respectively. The expected sensitivity of the h(b b) + E miss T signal is estimated from the model-independent upper limits on the visible cross section and the product A • of the signal acceptance A and reconstruction efficiency provided by ATLAS in the auxiliary material of [18]. In this way upper limits on the signal strength in each of the analysis regions are derived that are then statistically combined to obtain the total expected sensitivity.…”

“…In this combination it is assumed that the signal contributions in the different analysis regions are independent of each other. We add that the h(b b) + E miss T search [18] provides at present the most stringent mono-X constraint for the 2HDM+a parameter scenario (5). This can be interfered for instance from the left plot in Figure 7 of the review article [22].…”

“…Γ (a → χ χ) ∝ y 2 χ cos 2 θ 0.005, meaning that in benchmark II even pseudoscalars with m a > 2m χ have large branching ratios into SM fermions. This feature also explains why in the case of (10) the h → inv bound [50,51] covers only the small triangular region with m a ∈ [0, 3.5] GeV and m χ < m a /2, and why the h(b b) + E miss T search [18] leads to no relevant constraint. 3 One also sees that the searches for pp → a → µ + µ − production [41,44,[46][47][48][49] allow to put severe constraints on the parameter space of benchmark II.…”