3,221 research outputs found
The Arp Ring: Galactic or extragalactic?
The Arp Ring is a faint, loop-like structure around the northern end of M81 which becomes apparent only on deep optical photographs of the galaxy. The nature of the Ring and its proximity to M81 are uncertain. Is it simply foreground structure, part of this galaxy, or is it within the M81 system? Infrared Astronomy Satellite (IRAS) maps of the region show a far-infrared counterpart of the Ring. The infrared data are compared with previous optical and radio observations to try to ascertain its physical nature. The poor correlation found between the common infrared/optical structure and the distribution of extragalactic neutral hydrogen, and the fact that its infrared properties are indistinguishable from those of nearby galactic cirrus, imply that the Arp Ring is simply a ring structure in the galactic cirrus
Collective Effects in Linear Spectroscopy of Dipole-Coupled Molecular Arrays
We present a consistent analysis of linear spectroscopy for arrays of nearest
neighbor dipole-coupled two-level molecules that reveals distinct signatures of
weak and strong coupling regimes separated for infinite size arrays by a
quantum critical point. In the weak coupling regime, the ground state of the
molecular array is disordered, but in the strong coupling regime it has
(anti)ferroelectric ordering. We show that multiple molecular excitations
(odd/even in weak/strong coupling regime) can be accessed directly from the
ground state. We analyze the scaling of absorption and emission with system
size and find that the oscillator strengths show enhanced superradiant behavior
in both ordered and disordered phases. As the coupling increases, the single
excitation oscillator strength rapidly exceeds the well known Heitler-London
value. In the strong coupling regime we show the existence of a unique spectral
transition with excitation energy that can be tuned by varying the system size
and that asymptotically approaches zero for large systems. The oscillator
strength for this transition scales quadratically with system size, showing an
anomalous one-photon superradiance. For systems of infinite size, we find a
novel, singular spectroscopic signature of the quantum phase transition between
disordered and ordered ground states. We outline how arrays of ultra cold
dipolar molecules trapped in an optical lattice can be used to access the
strong coupling regime and observe the anomalous superradiant effects
associated with this regime.Comment: 12 pages, 7 figures main tex
Global Positioning System constraints on fault slip rates in the Death Valley region, California and Nevada
We estimated horizontal velocities at 15 locations in the vicinity of Yucca Mountain, Nevada, from Global Positioning System surveys conducted between 1991 and 1996. We used these velocity estimates to infer slip rates on two major Quaternary faults within the eastern California shear zone (ECSZ), the Hunter Mountain and Death Valley faults. The sum of slip rates across the two faults is well determined at 5 ± 1 mm/yr (1-σ). Between 3 to 5 mm/yr of this motion appears to be accommodated along the Death Valley fault, implying 30–50 m of strain accumulation over the next 10,000 yr. If so, there is potential for 5 to 10 M_(w) 6.5–7.5 earthquakes during this period, a finding consistent with paleoseismological studies of the fault zone. Yucca Mountain, which lies 50 km east of the ECSZ, is the proposed location for the disposal of high-level nuclear waste in the United States
Search for minimal supergravity in single-electron events with jets and large missing transverse energy in pp-bar collisions at s√=1.8TeV
This is the publisher's version, also available electronically from http://journals.aps.org/prd/abstract/10.1103/PhysRevD.66.112001.We describe a search for evidence of minimal supergravity (MSUGRA) in 92.7pb(-1) of data collected with the DØ detector at the Fermilab Tevatron pp-bar collider at s√=1.8TeV. Events with a single electron, four or more jets, and large missing transverse energy were used in this search. The major backgrounds are from W+jets, misidentified multijet, tt-bar, and WW production. We observe no excess above the expected number of background events in our data. A new limit in terms of MSUGRA model parameters is obtained
Near-threshold production of -mesons in and NN collisions and -mixing
We consider near-threshold -meson production in and
collisions. An effective Lagrangian approach with one-pion exchange is applied
to analyze different contributions to the cross section for different isospin
channels. The Reggeon exchange mechanism is also evaluated for comparison. The
results from reactions are used to calculate the contribution of the
meson to the cross sections and invariant mass distributions
of the reactions and . It is found that
the experimental observation of mesons in the reaction is much more promising than the observation of mesons in
the reaction . Effects of isospin violation in the reactions
, , and , which are induced by -- mixing, are also analyzed.Comment: 43 pages, including 16 eps figures, to be bublished in Phys. Atom.
Nucl. (Yad. Fiz.) vol. 65, No. 11 (2002
Search for dilepton signatures from minimal low-energy supergravity in pp-bar collisions at s√=1.8 TeV
This is the publisher's version, also available electronically from http://journals.aps.org/prd/abstract/10.1103/PhysRevD.63.091102.We report on a search for supersymmetry using the DØ detector. The 1994–1996 data sample of s√=1.8 TeV pp-bar collisions was analyzed for events containing two leptons (e or μ), two or more jets, and missing transverse energy. Assuming the minimal supergravity model, with A(0)=0 and μ<0, various thresholds were employed to optimize the search. No events were found beyond expectation from the background. We set a lower limit at the 95% C.L. of 255 GeV/c(2) for equal mass squarks and gluinos for tanβ=2, and present exclusion contours in the (m(0),m(1/2)) plane for tanβ=2–6
Study of Zγ events and limits on anomalous ZZγ and Zγγ couplings in pp̄ collisions at s=1.96TeV
We present a measurement of the Zγ production cross section and limits on anomalous ZZγ and Zγγ couplings for form-factor scales of Λ=750 and 1000 GeV. The measurement is based on 138 (152) candidates in the eeγ (μμγ) final state using 320(290)pb-1 of pp̄ collisions at s=1.96TeV. The 95% C.L. limits on real and imaginary parts of individual anomalous couplings are |h10,30Z|<0.23, |h20,40Z|<0.020, |h10,30γ|<0.23, and |h20,40γ|<0.019 for Λ=1000GeV. © 2005 The American Physical Society
Design and Implementation of the New D0 Level-1 Calorimeter Trigger
Increasing luminosity at the Fermilab Tevatron collider has led the D0
collaboration to make improvements to its detector beyond those already in
place for Run IIa, which began in March 2001. One of the cornerstones of this
Run IIb upgrade is a completely redesigned level-1 calorimeter trigger system.
The new system employs novel architecture and algorithms to retain high
efficiency for interesting events while substantially increasing rejection of
background. We describe the design and implementation of the new level-1
calorimeter trigger hardware and discuss its performance during Run IIb data
taking. In addition to strengthening the physics capabilities of D0, this
trigger system will provide valuable insight into the operation of analogous
devices to be used at LHC experiments.Comment: 43 pages, 20 figures, version published in Nucl. Instrum. and Methods
Double Pomeron Opportunities at SQRT(s) = 1.8 Tev
I describe possible ways to discover hard double pomeron exchange (HDPE) with
the existing detectors at the Fermilab Tevatron, by using the small-angle
``luminosity'' counters as a veto. Estimates of the cross sections and
backgrounds are made. In addition to the intrinsic importance of HDPE, its
observation would be useful for calibrating the detectors, and for estimating
the ``survival probability'' of rapidity gaps.Comment: 8 pages, LaTeX, 1 PostScript figure availble from the author
([email protected]), MSUHEP-93-0
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