We performed high-pressure x-ray diffraction (XRD), Raman, and transport measurements combined with first-principles calculations to investigate the behavior of tin diselenide (SnSe2) under compression. The obtained s...
详细信息
We performed high-pressure x-ray diffraction (XRD), Raman, and transport measurements combined with first-principles calculations to investigate the behavior of tin diselenide (SnSe2) under compression. The obtained single-crystal XRD data indicate the formation of a (1/3,1/3,0)-type superlattice above 17 GPa. According to our density functional theory results, the pressure-induced transition to the commensurate periodic lattice distortion (PLD) phase is due to the combined effect of strong Fermi surface nesting and electron-phonon coupling at a momentum wave vector q=(1/3,1/3,0). In contrast, similar PLD transitions associated with charge density wave (CDW) orderings in transition metal dichalcogenides (TMDs) do not involve significant Fermi surface nesting. The discovered pressure-induced PLD is quite remarkable, as pressure usually suppresses CDW phases in related materials. Our findings, therefore, provide new playgrounds to study the intricate mechanisms governing the emergence of PLD in TMD-related materials.
A search for long-lived particles (LLPs) using 140 fb−1 of pp collision data with s=13 TeV recorded by the ATLAS experiment at the LHC is presented. The search targets LLPs with masses between 5 and 55 GeV that deca...
详细信息
A search for long-lived particles (LLPs) using 140 fb−1 of pp collision data with s=13 TeV recorded by the ATLAS experiment at the LHC is presented. The search targets LLPs with masses between 5 and 55 GeV that decay hadronically in the ATLAS inner detector. Benchmark models with LLP pair production from exotic decays of the Higgs boson and models featuring long-lived axionlike particles (ALPs) are considered. No significant excess above the expected background is observed. Upper limits are placed on the branching ratio of the Higgs boson to pairs of LLPs, the cross section for ALPs produced in association with a vector boson, and, for the first time, on the branching ratio of the top quark to an ALP and a u/c quark.
Statistical combinations of searches for charginos and neutralinos using various decay channels are performed using 139 fb−1 of pp collision data at s=13 TeV with the ATLAS detector at the Large Hadron Collider. Sea...
详细信息
Statistical combinations of searches for charginos and neutralinos using various decay channels are performed using 139 fb−1 of pp collision data at s=13 TeV with the ATLAS detector at the Large Hadron Collider. Searches targeting pure-wino chargino pair production, pure-wino chargino-neutralino production, or Higgsino production decaying via standard model W, Z, or h bosons are combined to extend the mass reach to the produced supersymmetric particles by 30–100 GeV. The depth of the sensitivity of the original searches is also improved by the combinations, lowering the 95% C.L. cross-section upper limits by 15%–40%.
The associated production of Higgs and W bosons via vector-boson fusion is highly sensitive to the relative sign of the Higgs boson couplings to W and Z bosons. In this Letter, two searches for this process are presen...
详细信息
The associated production of Higgs and W bosons via vector-boson fusion is highly sensitive to the relative sign of the Higgs boson couplings to W and Z bosons. In this Letter, two searches for this process are presented, using 140 fb−1 of proton-proton collision data at s=13 TeV recorded by the ATLAS detector at the LHC. The first search targets scenarios with opposite-sign couplings of the W and Z bosons to the Higgs boson, while the second targets standard model-like scenarios with same-sign couplings. Both analyses consider Higgs boson decays into a pair of b quarks and W boson decays with an electron or muon. The data exclude the opposite-sign coupling hypothesis with a significance beyond 5σ, and the observed (expected) upper limit set on the cross section for vector-boson fusion WH production is 9.0 (8.7) times the standard model value at 95% confidence level.
A combination of searches for a new resonance decaying into a Higgs boson pair is presented, using up to 139 fb−1 of pp collision data at s=13 TeV recorded with the ATLAS detector at the LHC. The combination include...
详细信息
A combination of searches for a new resonance decaying into a Higgs boson pair is presented, using up to 139 fb−1 of pp collision data at s=13 TeV recorded with the ATLAS detector at the LHC. The combination includes searches performed in three decay channels: bb¯bb¯, bb¯τ+τ−, and bb¯γγ. No excess above the expected Standard Model background is observed and upper limits are set at the 95% confidence level on the production cross section of Higgs boson pairs originating from the decay of a narrow scalar resonance with mass in the range 251 GeV–5 TeV. The observed (expected) limits are in the range 0.96–600 fb (1.2–390 fb). The limits are interpreted in the type-I two-Higgs-doublet model and the minimal supersymmetric standard model, and constrain parameter space not previously excluded by other searches.
This Letter presents results from a combination of searches for Higgs boson pair production using 126–140 fb−1 of proton-proton collision data at s=13 TeV recorded with the ATLAS detector. At 95% confidence level (...
详细信息
This Letter presents results from a combination of searches for Higgs boson pair production using 126–140 fb−1 of proton-proton collision data at s=13 TeV recorded with the ATLAS detector. At 95% confidence level (CL), the upper limit on the production rate is 2.9 times the standard model (SM) prediction, with an expected limit of 2.4 assuming no Higgs boson pair production. Constraints on the Higgs boson self-coupling modifier κλ=λHHH/λHHHSM, and the quartic HHVV coupling modifier κ2V=gHHVV/gHHVVSM, are derived individually, fixing the other parameter to its SM value. The observed 95% CL intervals are −1.2<κλ<7.2 and 0.6<κ2V<1.5, respectively, while the expected intervals are −1.6<κλ<7.2 and 0.4<κ2V<1.6 in the SM case. Constraints obtained for several interaction parameters within Higgs effective field theory are the strongest to date, offering insights into potential deviations from SM predictions.
Higgsinos with masses near the electroweak scale can solve the hierarchy problem and provide a dark matter candidate, while detecting them at the LHC remains challenging if their mass splitting is O(1 GeV). This Lett...
详细信息
Higgsinos with masses near the electroweak scale can solve the hierarchy problem and provide a dark matter candidate, while detecting them at the LHC remains challenging if their mass splitting is O(1 GeV). This Letter presents a novel search for nearly mass-degenerate Higgsinos in events with an energetic jet, missing transverse momentum, and a low-momentum track with a significant transverse impact parameter using 140 fb−1 of proton-proton collision data at s=13 TeV collected by the ATLAS experiment. For the first time since LEP, a range of mass splittings between the lightest charged and neutral Higgsinos from 0.3 to 0.9 GeV is excluded at 95% confidence level, with a maximum reach of approximately 170 GeV in the Higgsino mass.
Angular correlations between heavy quarks provide a unique probe of the quark-gluon plasma created in ultrarelativistic heavy-ion collisions. Results are presented of a measurement of the azimuthal angle correlations ...
详细信息
Angular correlations between heavy quarks provide a unique probe of the quark-gluon plasma created in ultrarelativistic heavy-ion collisions. Results are presented of a measurement of the azimuthal angle correlations between muons originating from semileptonic decays of heavy quarks produced in 5.02 TeV Pb+Pb and pp collisions at the LHC. The muons are measured with transverse momenta and pseudorapidities satisfying pTμ>4 GeV and |ημ|<2.4, respectively. The distributions of azimuthal angle separation Δϕ for muon pairs having pseudorapidity separation |Δη|>0.8, are measured in different Pb+Pb centrality intervals and compared to the same distribution measured in pp collisions at the same center-of-mass energy. Results are presented separately for muon pairs with opposite-sign charges, same-sign charges, and all pairs. A clear peak is observed in all Δϕ distributions at Δϕ∼π, consistent with the parent heavy-quark pairs being produced via hard-scattering processes. The widths of that peak, characterized using Cauchy-Lorentz fits to the Δϕ distributions, are found to not vary significantly as a function of Pb+Pb collision centrality and are similar for pp and Pb+Pb collisions. This observation will provide important constraints on theoretical descriptions of heavy-quark interactions with the quark-gluon plasma.
This Letter presents the first study of the energy dependence of diboson polarization fractions in WZ→ℓνℓ′ℓ′(ℓ,ℓ′=e,μ) production. The dataset used corresponds to an integrated luminosity of 140 fb−1 of proton-...
详细信息
This Letter presents the first study of the energy dependence of diboson polarization fractions in WZ→ℓνℓ′ℓ′(ℓ,ℓ′=e,μ) production. The dataset used corresponds to an integrated luminosity of 140 fb−1 of proton-proton collisions at a center-of-mass energy of 13 TeV recorded by the ATLAS detector. Two fiducial regions with an enhanced presence of events featuring two longitudinally polarized bosons are defined. A nonzero fraction of events with two longitudinally polarized bosons is measured with an observed significance of 5.3 standard deviations in the region with 100200 GeV, where pTZ is the transverse momentum of the Z boson. This Letter also reports the first study of the radiation-amplitude-zero effect. Events with two transversely polarized bosons are analyzed for the ΔY(ℓWZ) and ΔY(WZ) distributions defined respectively as the rapidity difference between the lepton from the W boson decay and the Z boson and the rapidity difference between the W boson and the Z boson. Significant suppression of events near zero is observed in both distributions. Unfolded ΔY(ℓWZ) and ΔY(WZ) distributions are also measured and compared to theoretical predictions.
A search for the exclusive hadronic decays W±→π±γ, W±→K±γ, and W±→ρ±γ is performed using up to 140 fb−1 of proton-proton collisions recorded with the ATLAS detector at a center-o...
详细信息
A search for the exclusive hadronic decays W±→π±γ, W±→K±γ, and W±→ρ±γ is performed using up to 140 fb−1 of proton-proton collisions recorded with the ATLAS detector at a center-of-mass energy of s=13 TeV. If observed, these rare processes would provide a unique test bench for the quantum chromodynamics factorization formalism used to calculate cross sections at colliders. Additionally, at future colliders, these decays could offer a new way to measure the W boson mass through fully reconstructed decay products. The search results in the most stringent upper limits to date on the branching fractions B(W±→π±γ)<1.9×10−6, B(W±→K±γ)<1.7×10−6, B(W±→ρ±γ)<5.2×10−6 at 95% confidence level.
暂无评论