Edge-control and surface-smoothness in sub-aperture polishing of mirror segments

This paper addresses two challenges in establishing a new process chain for polishing hexagonal segments for extremely large telescopes:- i) control of edge and corner profiles in small-tool polishing of hexagons, and ii) achieving the required smoothness of the bulk aspheric form. We briefly describe the performance of a CNC-grinding process used to create the off-axis asphere, which established the input-quality for subsequent processing. We then summarize processes for smoothing ground mid-spatials and pre- and corrective polishing using Zeeko CNC machines. The impact of two cases is considered; i) all processing stages are performed after the segment is cut hexagonal, and ii) final rectification of a hexagon after cutting from an aspherised roundel, as an alternative to ionfiguring. We then report on experimental results on witness samples demonstrating edges and corners close to the EELT segment specification, and results on a full-aperture spherical segment showing excellent surface smoothness. © 2012 SPIE

Studies of new Higgs boson interactions through nonresonant HH production in the b¯bγγ fnal state in pp collisions at √s = 13 TeV with the ATLAS detector

A search for nonresonant Higgs boson pair production in the b ¯bγγ fnal state is performed using 140 fb−1 of proton-proton collisions at a centre-of-mass energy of 13 TeV recorded by the ATLAS detector at the CERN Large Hadron Collider. This analysis supersedes and expands upon the previous nonresonant ATLAS results in this fnal state based on the same data sample. The analysis strategy is optimised to probe anomalous values not only of the Higgs (H) boson self-coupling modifer κλ but also of the quartic HHV V (V = W, Z) coupling modifer κ2V . No signifcant excess above the expected background from Standard Model processes is observed. An observed upper limit µHH < 4.0 is set at 95% confdence level on the Higgs boson pair production cross-section normalised to its Standard Model prediction. The 95% confdence intervals for the coupling modifers are −1.4 < κλ < 6.9 and −0.5 < κ2V < 2.7, assuming all other Higgs boson couplings except the one under study are fxed to the Standard Model predictions. The results are interpreted in the Standard Model efective feld theory and Higgs efective feld theory frameworks in terms of constraints on the couplings of anomalous Higgs boson (self-)interactions

Combination of searches for heavy spin-1 resonances using 139 fb−1 of proton-proton collision data at s = 13 TeV with the ATLAS detector

A combination of searches for new heavy spin-1 resonances decaying into different pairings of W, Z, or Higgs bosons, as well as directly into leptons or quarks, is presented. The data sample used corresponds to 139 fb−1 of proton-proton collisions at = 13 TeV collected during 2015–2018 with the ATLAS detector at the CERN Large Hadron Collider. Analyses selecting quark pairs (qq, bb, , and tb) or third-generation leptons (τν and ττ) are included in this kind of combination for the first time. A simplified model predicting a spin-1 heavy vector-boson triplet is used. Cross-section limits are set at the 95% confidence level and are compared with predictions for the benchmark model. These limits are also expressed in terms of constraints on couplings of the heavy vector-boson triplet to quarks, leptons, and the Higgs boson. The complementarity of the various analyses increases the sensitivity to new physics, and the resulting constraints are stronger than those from any individual analysis considered. The data exclude a heavy vector-boson triplet with mass below 5.8 TeV in a weakly coupled scenario, below 4.4 TeV in a strongly coupled scenario, and up to 1.5 TeV in the case of production via vector-boson fusion

Measurement of the centrality dependence of the dijet yield in p+Pb collisions at √sNN = 8.16 TeV with the ATLAS detector

ATLAS measured the centrality dependence of the dijet yield using 165     nb − 1 of p + Pb data collected at √ s NN = 8.16     TeV in 2016. The event centrality, which reflects the p + Pb impact parameter, is characterized by the total transverse energy registered in the Pb-going side of the forward calorimeter. The central-to-peripheral ratio of the scaled dijet yields, R CP , is evaluated, and the results are presented as a function of variables that reflect the kinematics of the initial hard parton scattering process. The R CP shows a scaling with the Bjorken x of the parton originating from the proton, x p , while no such trend is observed as a function of x Pb . This analysis provides unique input to understanding the role of small proton spatial configurations in p + Pb collisions by covering parton momentum fractions from the valence region down to x p ∼ 10 − 3 and x Pb ∼ 4 × 10 − 4

Search for direct production of electroweakinos in final states with one lepton, jets and missing transverse momentum in pp collisions at √s = 13 TeV with the ATLAS detector

Searches for electroweak production of wino-like chargino pairs, χ~1+χ~1−, and of wino-like chargino and next-to-lightest neutralino, χ~1±χ~20, are presented. The models explored assume that the charginos decay into a W boson and the lightest neutralino, χ~1±→W±χ~10. The next-to-lightest neutralinos are degenerate in mass with the chargino and decay to χ~10 and either a Z or a Higgs boson, χ~20→Zχ~10 or hχ~10. The searches exploit the presence of a single isolated lepton and missing transverse momentum from the W boson decay products and the lightest neutralinos, and the presence of jets from hadronically decaying Z or W bosons or from the Higgs boson decaying into a pair of b-quarks. The searches use 139 fb−1 of √s = 13 TeV proton-proton collisions data collected by the ATLAS detector at the Large Hadron Collider between 2015 and 2018. No deviations from the Standard Model expectations are found, and 95% confidence level exclusion limits are set. Chargino masses ranging from 260 to 520 GeV are excluded for a massless χ~10 in chargino pair production models. Degenerate chargino and next-to-lightest neutralino masses ranging from 260 to 420 GeV are excluded for a massless χ~10 for χ~20→Zχ~10. For decays through an on-shell Higgs boson and for mass-splitting between χ~1±/χ~20 and χ~10 as small as the Higgs boson mass, mass limits are improved by up to 40 GeV in the range of 200–260 GeV and 280–470 GeV compared to previous ATLAS constraints

A search for R-parity-violating supersymmetry in final states containing many jets in pp collisions at √s = 13 TeV with the ATLAS detector

A search for R-parity-violating supersymmetry in final states with high jet multiplicity is presented. The search uses 140 fb−1 of proton-proton collision data at √s = 13 TeV collected by the ATLAS experiment during Run 2 of the Large Hadron Collider. The results are interpreted in the context of R-parity-violating supersymmetry models that feature prompt gluino-pair production decaying directly to three jets each or decaying to two jets and a neutralino which subsequently decays promptly to three jets. No significant excess over the Standard Model expectation is observed and exclusion limits at the 95% confidence level are extracted. Gluinos with masses up to 1800 GeV are excluded when decaying directly to three jets. In the cascade scenario, gluinos with masses up to 2340 GeV are excluded for a neutralino with mass up to 1250 GeV

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 q q b b final state using data recorded by the ATLAS detector at the LHC in proton-proton collisions at √ s = 13     TeV and corresponding to an integrated luminosity of 137     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 ¯ 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 V H 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 μ = 1.4 + 1.0 − 0.9 and the corresponding cross section is 3.1 ± 1.3 ( stat ) + 1.8 − 1.4 ( syst )     pb

Search for a CP-odd Higgs boson decaying into a heavy CP-even Higgs boson and a Z boson in the ℓ+ℓ−tt¯ and νν¯bb¯ final states using 140 fb−1 of data collected with the ATLAS detector

A search for a heavy CP-odd Higgs boson, A, decaying into a Z boson and a heavy CP-even Higgs boson, H, is presented. It uses the full LHC Run 2 dataset of pp collisions at √s = 13 TeV collected with the ATLAS detector, corresponding to an integrated luminosity of 140 fb−1. The search for A → ZH is performed in the ℓ+ℓ−tt¯ and νν¯bb¯ final states and surpasses the reach of previous searches in different final states in the region with mH > 350 GeV and mA > 800 GeV. No significant deviation from the Standard Model expectation is found. Upper limits are placed on the production cross-section times the decay branching ratios. Limits with less model dependence are also presented as functions of the reconstructed m(tt¯) and m(bb¯) distributions in the ℓ+ℓ−tt¯ and νν¯bb¯ channels, respectively. In addition, the results are interpreted in the context of two-Higgs-doublet models