428 research outputs found
The spin content of the proton in full QCD
We present preliminary results on the proton spin structure function in full
QCD. The measurement has been done using 4 flavours of staggered fermions and
an improved definition of the lattice topological charge density.Comment: 3 pages, 3 figures, contribution to Lattice-97. Latex file including
espcrc2.sty. The colour of a line in the first figure has been changed to
avoid problems on some printer
Exploring the BEC-BCS Crossover with an Ultracold Gas of Li Atoms
We present an overview of our recent measurements on the crossover from a
Bose-Einstein condensate of molecules to a Bardeen-Cooper-Schrieffer
superfluid. The experiments are performed on a two-component spin-mixture of
Li atoms, where a Fesh\-bach resonance serves as the experimental key to
tune the s-wave scattering length and thus to explore the various interaction
regimes. In the BEC-BCS crossover, we have characterized the interaction energy
by measuring the size of the trapped gas, we have studied collective excitation
modes, and we have observed the pairing gap. Our observations provide strong
evidence for superfluidity in the strongly interacting Fermi gas.Comment: Proceedings of ICAP-2004 (Rio de Janeiro). Review on Innsbruck
BEC-BCS crossover experiments with updated Feshbach resonance positio
Finite-Temperature Collective Dynamics of a Fermi Gas in the BEC-BCS Crossover
We report on experimental studies on the collective behavior of a strongly
interacting Fermi gas with tunable interactions and variable temperature. A
scissors mode excitation in an elliptical trap is used to characterize the
dynamics of the quantum gas in terms of hydrodynamic or near-collisionless
behavior. We obtain a crossover phase diagram for collisional properties,
showing a large region where a non-superfluid strongly interacting gas shows
hydrodynamic behavior. In a narrow interaction regime on the BCS side of the
crossover, we find a novel temperature-dependent damping peak, suggesting a
relation to the superfluid phase transition
Precision Measurements of Collective Oscillations in the BEC-BCS Crossover
We report on precision measurements of the frequency of the radial
compression mode in a strongly interacting, optically trapped Fermi gas of Li-6
atoms. Our results allow for a test of theoretical predictions for the equation
of state in the BEC-BCS crossover. We confirm recent quantum Monte-Carlo
results and rule out simple mean-field BCS theory. Our results show the
long-sought beyond-mean-field effects in the strongly interacting BEC regime.Comment: improved discussion of small ellipticity and anharmonicity
correction
Collective excitations of a degenerate gas at the BEC-BCS crossover
We study collective excitation modes of a fermionic gas of Li atoms in
the BEC-BCS crossover regime. While measurements of the axial compression mode
in the cigar-shaped trap close to a Feshbach resonance confirm theoretical
expectations, the radial compression mode shows surprising features. In the
strongly interacting molecular BEC regime we observe a negative frequency shift
with increasing coupling strength. In the regime of a strongly interacting
Fermi gas, an abrupt change in the collective excitation frequency occurs,
which may be a signature for a transition from a superfluid to a collisionless
phase.Comment: Feshbach resonance position updated, few minor change
Coupling Constants for Scalar Glueball Decay
We evaluate the partial decay widths of the lightest scalar glueball to pairs
of pseudoscalar quark-antiquark states. The calculation is done in the valence
(quenched) approximation on a 16^3 \time 24 lattice at . These
predictions and values obtained earlier for the infinite volume continuum limit
of the scalar glueball's mass are in good agreement with the observed
properties of and inconsistent with all other observed meson
resonances.Comment: 8 pages of Latex, 12 PostScript figures, 2 macros included, plenary
talk given by D. Weingarten at Lattice 95, to appear in conference
proceeding
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