1,931 research outputs found
Optical measurement of heteronuclear cross-relaxation interactions in Tm:YAG
We investigate cross-relaxation interactions between Tm and Al in Tm:YAG
using two optical methods: spectral holeburning and stimulated echoes. These
interactions lead to a reduction in the hyperfine lifetime at magnetic fields
that bring the Tm hyperfine transition into resonance with an Al transition. We
develop models for measured echo decay curves and holeburning spectra near a
resonance, which are used to show that the Tm-Al interaction has a resonance
width of 10~kHz and reduces the hyperfine lifetime to 0.5 ms. The antihole
structure is consistent with an interaction dominated by the Al nearest
neighbors at 3.0 Angstroms, with some contribution from the next nearest
neighbors at 3.6 Angstroms.Comment: 13 pages, 9 figure
Spin coherence lifetime extension in Tm:YAG through dynamical decoupling
We report on spin coherence lifetime extension on Tm:YAG obtained
through dynamically decoupling the thulium spins from their magnetic
environment. The coherence lifetime reached with a Carr-Purcell-Meiboom-Gill
sequence revealed a 450-fold extension [ ms] with respect
to previously measured values. Comparison to a simple theoretical model allowed
us to estimate the correlation time of the fluctuations of the ground level
transition frequency to s at 1.7 K. For attaining efficient
decoupling sequences, we developed a strategy inspired by the
\emph{zero-first-order Zeeman} effect to minimize the large inhomogeneous
broadening of the ground level spin transition.Comment: 10 pages, 7 figure
Lifetime of sub-THz coherent acoustic phonons in a GaAs-AlAs superlattice
We measure the lifetime of the zone-center 340 GHz longitudinal phonon mode in a GaAs-AlAs superlattice excited and probed with femtosecond laser pulses. By comparing measurements conducted at room temperature and liquid nitrogen temperature, we separate the intrinsic (phonon-phonon scattering) and extrinsic contributions to phonon relaxation. The estimated room temperature intrinsic lifetime of 0.95 ns is compared to available calculations and experimental data for bulk GaAs. We conclude that ∼0.3 THz phonons are in the transition zone between Akhiezer and Landau-Rumer regimes of phonon-phonon relaxation at room temperature.United States. Dept. of Energy. Office of Basic Energy Sciences (Award DE-SC0001299)United States. Dept. of Energy (Grant DE-FG02-00ER15087
A comprehensive approach to analyzing the XMM-Newton data of Seyfert 1 galaxies
Aims. We seek a comprehensive analysis of all the information provided by the
XMM-Newton satellite of the four Seyfert 1 galaxies ESO 359-G19, HE 1143-1810,
CTS A08.12, and Mrk 110, including the UV range, to characterize the different
components that are emitting and absorbing radiation in the vicinity of the
active nucleus.
Methods. The continuum emission was studied through the EPIC spectra by
taking advantage of the spectral range of these cameras. The high-resolution
RGS spectra were analyzed to characterize the absorbing and emission line
features that arise in the spectra of the sources. All these data, complemented
by information in the UV, are analyzed jointly in order to achieve a consistent
characterization of the observed features in each object.
Results. The continuum emission of the sources can be characterized either by
a combination of a power law and a black body for the weakest objects or by two
power law components for the brightest ones. The continuum is not absorbed by
neutral or ionized material in the line of sight to any of these sources. In
all of them we have identified a narrow Fe-Kalpha line at 6.4 keV. In ESO
559-G19 we also find an FeXXVI line at about 7 keV. In the soft X-rays band, we
identify only one OVII line in the spectra of HE 1143-1810 and CTS A08.12, and
two OVII-He alpha triplets and a narrow OVIII-Ly alpha emission line in Mrk
110.
Conclusions. Not detecting warm material in the line of sight to the low
state objects is due to intrinsically weaker or absent absorption in the line
of sight and not to a low signal-to-noise ratio in the data. Besides this, the
absence of clear emission lines cannot be fully attributed to dilution of those
lines by a strong continuum.Comment: 14 pages, 7 figures, 9 tables, accepted by A&
Intrinsic to extrinsic phonon lifetime transition in a GaAs–AlAs superlattice
We have measured the lifetimes of two zone-center longitudinal acoustic phonon modes, at 320 and 640 GHz, in a 14 nm GaAs/2 nm AlAs superlattice structure. By comparing measurements at 296 and 79 K we separate the intrinsic contribution to phonon lifetime determined by phonon–phonon scattering from the extrinsic contribution due to defects and interface roughness. At 296 K, the 320 GHz phonon lifetime has approximately equal contributions from intrinsic and extrinsic scattering, whilst at 640 GHz it is dominated by extrinsic effects. These measurements are compared with intrinsic and extrinsic scattering rates in the superlattice obtained from first-principles lattice dynamics calculations. The calculated room-temperature intrinsic lifetime of longitudinal phonons at 320 GHz is in agreement with the experimentally measured value of 0.9 ns. The model correctly predicts the transition from predominantly intrinsic to predominantly extrinsic scattering; however the predicted transition occurs at higher frequencies. Our analysis indicates that the 'interfacial atomic disorder' model is not entirely adequate and that the observed frequency dependence of the extrinsic scattering rate is likely to be determined by a finite correlation length of interface roughness.United States. Dept. of Energy. Office of Basic Energy Sciences (Award DE-FG02-00ER15087)United States. Dept. of Energy. Office of Basic Energy Sciences (Award DE-SC0001299/DE-FG02-09ER46577
Calculation of The Band Gap Energy and Study of Cross Luminescence in Alkaline-Earth Dihalide Crystals
The band gap energy as well as the possibility of cross luminescence
processes in alkaline-earth dihalide crystals have been calculated using the ab
initio Perturbed-Ion (PI) model. The gap is calculated in several ways: as a
difference between one-electron energy eigenvalues and as a difference between
total energies of appropriate electronic states of the crystal, both at the HF
level and with inclusion of Coulomb correlation effects. In order to study the
possibility of ocurrence of cross luminescence in these materials, the energy
difference between the valence band and the upmost core band for some
representative crystals has been calculated. Both calculated band gap energies
and cross luminescence predictions compare very well with the available
experimental results.Comment: LaTeX file containing 8 pages plus 1 postscript figure. Final version
accepted for publication in The Journal of the Physical Society of Japan. It
contains a more complete list of references, as well as a more detailed
comparison with previous theoretical investigations on the subjec
Characterization of the emitting and absorbing media around the nucleus of the active galaxy UGC11763 using XMM-Newton data
Aims. The detailed analysis of all data taken by the XMM-Newton satellite of
UGC11763 to characterize the different components that are emitting and
absorbing radiation in the vicinity of the active nucleus.
Methods. The continuum emission was studied through the EPIC spectra taking
profit of the spectral range of these cameras. The high resolution RGS spectra
were analyzed in order to characterize the absorbing features and the emission
line features that arise in the spectra of this source.
Results. A power law with a photon index \Gamma = 1.72^{+0.03}_{-0.01}
accounts for the continuum emission of this source in the hard X-rays from 10
down to 1 keV. At lower energies, a black body model with kT= 0.100\pm 0.003
keV provides a good description of the observed soft excess. The absorption
signatures in the spectra of UGC11763 are consistent with the presence of a two
phase ionized material (log U=1.65^{+0.07}_{-0.08}; 2.6\pm 0.1 and log N_{H} =
21.2\pm 0.2; 21.51\pm 0.01 cm^{-2}, respectively) in the line of sight. The
physical conditions found are consistent with the two phases being in pressure
equilibrium. The low ionization component is more ionized than typically found
for warm absorbers in other Seyfert 1 galaxies. There are also signatures of
some emission lines: Ovii He(r), Ovii He(f), a blend of the
Neix He triplet and Fexviii at \lambda 17.5 \AA.Comment: 11 pages, 10 figures, accepted to be published by A&
Measurement of the cross-section and charge asymmetry of bosons produced in proton-proton collisions at TeV with the ATLAS detector
This paper presents measurements of the and cross-sections and the associated charge asymmetry as a
function of the absolute pseudorapidity of the decay muon. The data were
collected in proton--proton collisions at a centre-of-mass energy of 8 TeV with
the ATLAS experiment at the LHC and correspond to a total integrated luminosity
of 20.2~\mbox{fb^{-1}}. The precision of the cross-section measurements
varies between 0.8% to 1.5% as a function of the pseudorapidity, excluding the
1.9% uncertainty on the integrated luminosity. The charge asymmetry is measured
with an uncertainty between 0.002 and 0.003. The results are compared with
predictions based on next-to-next-to-leading-order calculations with various
parton distribution functions and have the sensitivity to discriminate between
them.Comment: 38 pages in total, author list starting page 22, 5 figures, 4 tables,
submitted to EPJC. All figures including auxiliary figures are available at
https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2017-13
Search for chargino-neutralino production with mass splittings near the electroweak scale in three-lepton final states in √s=13 TeV pp collisions with the ATLAS detector
A search for supersymmetry through the pair production of electroweakinos with mass splittings near the electroweak scale and decaying via on-shell W and Z bosons is presented for a three-lepton final state. The analyzed proton-proton collision data taken at a center-of-mass energy of √s=13 TeV were collected between 2015 and 2018 by the ATLAS experiment at the Large Hadron Collider, corresponding to an integrated luminosity of 139 fb−1. A search, emulating the recursive jigsaw reconstruction technique with easily reproducible laboratory-frame variables, is performed. The two excesses observed in the 2015–2016 data recursive jigsaw analysis in the low-mass three-lepton phase space are reproduced. Results with the full data set are in agreement with the Standard Model expectations. They are interpreted to set exclusion limits at the 95% confidence level on simplified models of chargino-neutralino pair production for masses up to 345 GeV
Search for new phenomena in final states with an energetic jet and large missing transverse momentum in pp collisions at √ s = 8 TeV with the ATLAS detector
Results of a search for new phenomena in final states with an energetic jet and large missing transverse momentum are reported. The search uses 20.3 fb−1 of √ s = 8 TeV data collected in 2012 with the ATLAS detector at the LHC. Events are required to have at least one jet with pT > 120 GeV and no leptons. Nine signal regions are considered with increasing missing transverse momentum requirements between Emiss T > 150 GeV and Emiss T > 700 GeV. Good agreement is observed between the number of events in data and Standard Model expectations. The results are translated into exclusion limits on models with either large extra spatial dimensions, pair production of weakly interacting dark matter candidates, or production of very light gravitinos in a gauge-mediated supersymmetric model. In addition, limits on the production of an invisibly decaying Higgs-like boson leading to similar topologies in the final state are presente
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