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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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The ZZ production cross section in proton-proton collisions at 13 TeV center-of-mass energy is measured using 3.2 fb$^{-1}$ of data recorded with the ATLAS detector at the Large Hadron Collider. The considered Z boson candidates decay to an electron or muon pair of mass 66-116 GeV. The cross section is measured in a fiducial phase space reflecting the detector acceptance. It is also extrapolated to a total phase space for Z bosons in the same mass range and of all decay modes, giving $16.7^{+2.2}_{-2.0}$(stat)$ ^{+0.9}_{-0.7}$(syst)$ ^{+1.0}_{-0.7}$(lumi) pb. The results agree with standard model predictions.
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Particle detectors record the interactions of subatomic particles and their passage through matter. The identification of these particles is necessary for in-depth physics analysis. While particles can be identified by their individual behavior as they travel through matter, the full context of the interaction in which they are produced can aid the classification task substantially. We have developed the first convolutional neural network for particle identification which uses context information. This is also the first implementation of a four-tower siamese-type architecture both for separation of independent inputs and inclusion of context information. The network classifies clusters of energy deposits from the NOvA neutrino detectors as electrons, muons, photons, pions, and protons with an overall efficiency and purity of 83.3% and 83.5%, respectively. We show that providing the network with context information improves performance by comparing our results with a network trained without context information.
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Under the expectation that nature is natural, we extend the Standard Model to include SUSY to stabilize the electroweak sector and PQ symmetry to stabilize the QCD sector. Then natural SUSY arises from a Kim-Nilles solution to the SUSY μ problem which allows for a little hierarchy where μ~ $f$ $^{2}_{a}$/M P~ 100-300 GeV while the SUSY particle mass scale m SUSY~ 1-10 TeV >> μ. Dark matter then consists of two particles: a higgsino-like WIMP and a SUSY DFSZ axion. The range of allowed axion mass values m a depends on the mixed axion-higgsino relic density. Here, the range of m a is actually restricted in this case by limits on WIMPs from direct and indirect detection experiments. We plot the expected axion detection rate at microwave cavity experiments. The axion-photon-photon coupling is severely diminished by charged higgsino contributions to the anomalous coupling. In this case, the axion may retreat, at least temporarily, back into the regime of near invisibility. From our results, we urge new ideas for techniques which probe both deeper and more broadly into axion coupling versus axion mass parameter space.
Supersymmetric models with radiatively-driven electroweak naturalness require light higgsinos of mass ∼100–300 GeV. Naturalness in the QCD sector is invoked via the Peccei-Quinn (PQ) axion leading to mixed axion-higgsino dark matter. The SUSY DFSZ axion model provides a solution to the SUSY μ problem and the Little Hierarchy μ≪m{sub 3/2} may emerge as a consequence of a mismatch between PQ and hidden sector mass scales. The traditional gravitino problem is now augmented by the axino and saxion problems, since these latter particles can also contribute to overproduction of WIMPs or dark radiation, or violation of BBN constraints. We compute regions of the T{sub R} vs. m{sub 3/2} plane allowed by BBN, dark matter and dark radiation constraints for various PQ scale choices f{sub a}. These regions are compared to the values needed for thermal leptogenesis, non-thermal leptogenesis, oscillating sneutrino leptogenesis and Affleck-Dine leptogenesis. The latter three are allowed in wide regions of parameter space for PQ scale f{sub a}∼10{sup 10}–10{sup 12} GeV which is also favored by naturalness: f{sub a}∼√(μM{sub P}/λ{sub μ})∼10{sup 10}–10{sup 12} GeV. These f{sub a} values correspond to axion masses somewhat above the projected ADMX search regions.
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