4,787 research outputs found
Studies of highly-boosted top quarks near the TeV scale using jet masses at the LHC
Studies of highly-boosted top quarks produced inclusively in pp collisions at
14 TeV are discussed. The hadronic decays of boosted top quarks was studied in
a data-driven approach by analysing shapes of jet-mass distributions. Using
Monte Carlo models after a fast detector simulation, it is shown that inclusive
production of boosted top quarks can be observed if it has a cross section at
least twice larger than the prediction from the approximate
next-to-next-to-leading-order (aNNLO) calculation for the ttbar process. The
ttbar process with the nominal aNNLO strength can be measured using the masses
of jets after a b-tagging.Comment: 11 pages, 5 figure
Probing -Spin Correlations in Optical Lattices
We propose a technique to measure multi-spin correlation functions of
arbitrary range as determined by the ground states of spinful cold atoms in
optical lattices. We show that an observation of the atomic version of the
Stokes parameters, using focused lasers and microwave pulsing, can be related
to -spin correlators. We discuss the possibility of detecting not only
ground state static spin correlations, but also time-dependent spin wave
dynamics as a demonstrative example using our proposed technique.Comment: 7 pages, 4 figure
Chromosomal aberrations in a natural population of chironomus tentans exposed to chronic low-level environmental radiation
The salivary gland chromosomes of Chironomus tentans larvae collected from White Oak Creek, an area contaminated by radioactive waste from the Oak Ridge National Laboratory, and from six uncontaminated areas were examined for chromosomal aberrations. White Oak Creek populations were exposed to absorbed doses as high as 230 rads per year or about 1000 times background. Chromosomal maps were constructed to make a general comparison of the banding pattern of the salivary chromosomes of the C. tentans in the East Tennessee area with those of Canada and Europe. These maps were used as a reference in scoring aberrations. Fifteen different chromosomal aberrations were found in 365 larvae taken from the irradiated population as compared with five different aberrations observed in 356 larvae from six control populations, but the mean number of aberrations per larva did not differ in any of the populations. The quantitative amount of heterozygosity was essentially the same in the irradiated and the control population, but there were three times the variety of chromosomal aberrations found in the irradiated area. From this evidence it was concluded that chronic low-level irradiation from radioactive waste was increasing the variability of chromosomal aberrations without significantly increasing the frequency. It was also concluded that chromosomal polymorphism can be maintained in a natural population without superiority of the heterozygous individuals. (C.H.
Nearby Doorways, Parity Doublets and Parity Mixing in Compound Nuclear States
We discuss the implications of a doorway state model for parity mixing in
compound nuclear states. We argue that in order to explain the tendency of
parity violating asymmetries measured in Th to have a common sign,
doorways that contribute to parity mixing must be found in the same energy
neighbourhood of the measured resonance. The mechanism of parity mixing in this
case of nearby doorways is closely related to the intermediate structure
observed in nuclear reactions in which compound states are excited. We note
that in the region of interest (Th) nuclei exhibit octupole
deformations which leads to the existence of nearby parity doublets. These
parity doublets are then used as doorways in a model for parity mixing. The
contribution of such mechanism is estimated in a simple model.Comment: 11 pages, REVTE
Antiferromagnetic noise correlations in optical lattices
We analyze how noise correlations probed by time-of-flight (TOF) experiments
reveal antiferromagnetic (AF) correlations of fermionic atoms in
two-dimensional (2D) and three-dimensional (3D) optical lattices. Combining
analytical and quantum Monte Carlo (QMC) calculations using experimentally
realistic parameters, we show that AF correlations can be detected for
temperatures above and below the critical temperature for AF ordering. It is
demonstrated that spin-resolved noise correlations yield important information
about the spin ordering. Finally, we show how to extract the spin correlation
length and the related critical exponent of the AF transition from the noise.Comment: 4 pages, 4 figure
Fine Structure Discussion of Parity-Nonconserving Neutron Scattering at Epithermal Energies
The large magnitude and the sign correlation effect in the parity
non-conserving resonant scattering of epithermal neutrons from Th is
discussed in terms of a non-collective local doorway model. General
conclusions are drawn as to the probability of finding large parity violation
effects in other regions of the periodic table.Comment: 6 pages, Tex. CTP# 2296, to appear in Z. Phys.
Effective Spin Quantum Phases in Systems of Trapped Ions
A system of trapped ions under the action of off--resonant standing--waves
can be used to simulate a variety of quantum spin models. In this work, we
describe theoretically quantum phases that can be observed in the simplest
realization of this idea: quantum Ising and XY models. Our numerical
calculations with the Density Matrix Renormalization Group method show that
experiments with ion traps should allow one to access general properties of
quantum critical systems. On the other hand, ion trap quantum spin models show
a few novel features due to the peculiarities of induced effective spin--spin
interactions which lead to interesting effects like long--range quantum
correlations and the coexistence of different spin phases.Comment: 11 pages, 13 figure
Instability of charge ordered states in doped antiferromagnets
We analyze the induced interactions between localized holes in weakly-doped
Heisenberg antiferromagnets due to the modification of the quantum zero point
spin wave energy; i.e. the analogue of the Casimir effect. We show that this
interaction is uniformly attractive and falls off as r^{-2 d+1} in d
dimensions. For ``stripes'', i.e parallel (d-1)-dimensional hypersurfaces of
localized holes, the interaction energy per unit hyperarea is attractive and
falls, generically, like r^{-d}. We argue that, in the absence of a long-range
Coulomb repulsion between holes, this interaction leads to an instability of
any charge-ordered state in the dilute doping limit.Comment: Revtex, 5 pages two-column format, 3 ps figures (epsf). Two
references added and some textual change
Orientational phase transitions in anisotropic rare-earth magnets at low temperatures
Orientational phase transitions are investigated within the Heisenberg model
with single-site anisotropy. The temperature dependence of the cone angle is
calculated within the spin-wave theory. The role of the quantum
renormalizations of anisotropy constants is discussed. A comparison with the
experimental data on the cone-plane orientational transition in holmium is
performed.Comment: 9 pages, LaTeX, 3 figure
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