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Results for “substructuring”

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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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

EXPLORING HALO SUBSTRUCTURE WITH GIANT STARS: SUBSTRUCTURE IN THE LOCAL HALO AS SEEN IN THE GRID GIANT STAR SURVEY INCLUDING EXTENDED TIDAL DEBRIS FROM {omega}CENTAURI

We present the latitude-normalized radial velocity (v{sub b} ) distribution of 3318 subsolar metallicity, V {approx}< 13.5 stars from the Grid Giant Star Survey (GGSS) in southern hemisphere fields. The sample includes giants mostly within {approx}5 kpc from the Galactic disks and halo. The nearby halo is found to (1) exhibit significant kinematical substructure, and (2) be prominently represented by several velocity coherent structures, including a very retrograde 'cloud' of stars at l {approx} 285 Degree-Sign and extended, retrograde 'streams' visible as relatively tight l-v{sub b} sequences. One sequence in the fourth Galactic quadrant lies within the l-v{sub b} space expected to contain tidal debris from the 'star cluster' {omega}Centauri. Not only does {omega}Cen lie precisely in this l-v{sub b} sequence, but the positions and v{sub b} of member stars match those of N-body simulations of tidally disrupting dwarf galaxies on orbits ending with {omega}Cen's current position and space motion. But the ultimate proof that we have very likely found extended parts of the {omega}Cen tidal stream comes from echelle spectroscopy of a subsample of the stars that reveals a very particular chemical abundance signature known to occur only in {omega}Cen. The newly discovered {omega}Cen debris accounts for almost all fourth Galactic quadrant retrograde stars in the southern GGSS, which suggests {omega}Cen is a dominant contributor of retrograde giant stars in the inner Galaxy.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Improving LHC searches for dark photons using lepton-jet substructure

Collider signals of dark photons are an exciting probe for new gauge forces and are characterized by events with boosted lepton jets. Existing techniques are efficient in searching for muonic lepton jets but due to substantial backgrounds have difficulty constraining lepton jets containing only electrons. This is unfortunate since upcoming intensity frontier experiments are sensitive to dark photon masses which only allow electron decays. Analyzing a recently proposed model of kinetic mixing, with new scalar particles decaying into dark photons, we find that existing techniques for electron jets can be substantially improved. We show that using lepton-jet-substructure variables, in association with a boosted decision tree, improves background rejection, significantly increasing the LHC’s reach for dark photons in this region of parameter space.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗