4,776 research outputs found
Pseudorapidity Distribution of Charged Particles in PbarP Collisions at root(s)= 630GeV
Using a silicon vertex detector, we measure the charged particle
pseudorapidity distribution over the range 1.5 to 5.5 using data collected from
PbarP collisions at root s = 630 GeV. With a data sample of 3 million events,
we deduce a result with an overall normalization uncertainty of 5%, and typical
bin to bin errors of a few percent. We compare our result to the measurement of
UA5, and the distribution generated by the Lund Monte Carlo with default
settings. This is only the second measurement at this level of precision, and
only the second measurement for pseudorapidity greater than 3.Comment: 9 pages, 5 figures, LaTeX format. For ps file see
http://hep1.physics.wayne.edu/harr/harr.html Submitted to Physics Letters
Local/Non-Local Complementarity in Topological Effects
In certain topological effects the accumulation of a quantum phase shift is
accompanied by a local observable effect. We show that such effects manifest a
complementarity between non-local and local attributes of the topology, which
is reminiscent but yet different from the usual wave-particle complementarity.
This complementarity is not a consequence of non-commutativity, rather it is
due to the non-canonical nature of the observables. We suggest that a
local/non-local complementarity is a general feature of topological effects
that are ``dual'' to the AB effect.Comment: 4 page
Classical and Quantum Interaction of the Dipole
A unified and fully relativistic treatment of the interaction of the electric
and magnetic dipole moments of a particle with the electromagnetic field is
given. New forces on the particle due to the combined effect of electric and
magnetic dipoles are obtained. Four new experiments are proposed, three of
which would observe topological phase shifts.Comment: 10 pages, Latex/Revtex. Some minor errors have been correcte
Aharonov-Bohm scattering of charged particles and neutral atoms: the role of absorption
The Aharonov-Bohm scattering of charged particles by the magnetic field of an
infinitely long and infinitely thin solenoid (magnetic string) in an absorbing
medium is studied. We discuss the partial-wave approach to this problem and
show that standard partial-wave method can be adjusted to this case. The effect
of absorption leads to oscillations of the AB cross section.
Based on this we investigate the scattering of neutral atoms with induced
electric dipole moments by a charge wire of finite radius which is placed in an
uniform magnetic field. The physical realistic and practically important case
that all atoms which collide with the wire are totally absorbed at its surface,
is studied in detail. The dominating terms of the scattering amplitude are
evaluated analytically for different physical constellations. The rest terms
are written in a form suitable for a numerical computation. We show that if the
magnetic field is absent, the absorbing charged wire causes oscillations of the
cross section. In the presence of the magnetic field the cross section
increases and the dominating Aharonov--Bohm peak appears in the forward
direction, suppressing the oscillations.Comment: 15 pages, LaTeXfile, 2 figure
Algebraic Correlation Function and Anomalous Diffusion in the HMF model
In the quasi-stationary states of the Hamiltonian Mean-Field model, we
numerically compute correlation functions of momenta and diffusion of angles
with homogeneous initial conditions. This is an example, in a N-body
Hamiltonian system, of anomalous transport properties characterized by non
exponential relaxations and long-range temporal correlations. Kinetic theory
predicts a striking transition between weak anomalous diffusion and strong
anomalous diffusion. The numerical results are in excellent agreement with the
quantitative predictions of the anomalous transport exponents. Noteworthy, also
at statistical equilibrium, the system exhibits long-range temporal
correlations: the correlation function is inversely proportional to time with a
logarithmic correction instead of the usually expected exponential decay,
leading to weak anomalous transport properties
Band Gaps for Atoms in Light based Waveguides
The energy spectrum for a system of atoms in a periodic potential can exhibit
a gap in the band structure. We describe a system in which a laser is used to
produce a mechanical potential for the atoms, and a standing wave light field
is used to shift the atomic levels using the Autler-Townes effect, which
produces a periodic potential. The band structure for atoms guided by a hollow
optical fiber waveguide is calculated in three dimensions with quantised
external motion. The size of the band gap is controlled by the light guided by
the fiber. This variable band structure may allow the construction of devices
which can cool atoms. The major limitation on this device would be the
spontaneous emission losses.Comment: 7 pages, four postscript figures, uses revtex.sty, available through
http://online.anu.edu.au/Physics/papers/atom.htm
Mimicking a Squeezed Bath Interaction: Quantum Reservoir Engineering with Atoms
The interaction of an atomic two-level system and a squeezed vacuum leads to
interesting novel effects in atomic dynamics, including line narrowing in
resonance fluorescence and absorption spectra, and a suppressed (enhanced)
decay of the in-phase and out-of phase component of the atomic polarization. On
the experimental side these predictions have so far eluded observation,
essentially due to the difficulty of embedding atoms in a 4 pi squeezed vacuum.
In this paper we show how to ``engineer'' a squeezed-bath-type interaction for
an effective two-level system. In the simplest example, our two-level atom is
represented by the two ground levels of an atom with angular momentum J=1/2 ->
J=1/2 transition (a four level system) which is driven by (weak) laser fields
and coupled to the vacuum reservoir of radiation modes. Interference between
the spontaneous emission channels in optical pumping leads to a squeezed bath
type coupling, and thus to symmetry breaking of decay on the Bloch sphere. With
this system it should be possible to observe the effects predicted in the
context of squeezed bath - atom interactions. The laser parameters allow one to
choose properties of the squeezed bath interaction, such as the (effective)
photon number expectation number N and the squeezing phase phi. We present
results of a detailed analytical and numerical study.Comment: 24 pages, 8 figure
Dependence of the BEC transition temperature on interaction strength: a perturbative analysis
We compute the critical temperature T_c of a weakly interacting uniform Bose
gas in the canonical ensemble, extending the criterion of condensation provided
by the counting statistics for the uniform ideal gas. Using ordinary
perturbation theory, we find in first order , where T_c^0 is the transition temperature of the corresponding
ideal Bose gas, a is the scattering length, and is the particle number
density.Comment: 14 pages (RevTeX
States insensitive to the Unruh effect in multi-level detectors
We give a general treatment of the spontaneous excitation rates and the
non-relativistic Lamb shift of constantly accelerated multi-level atoms as a
model for multi-level detectors. Using a covariant formulation of the dipole
coupling between the atom and the electromagnetic field we show that new
Raman-like transitions can be induced by the acceleration. Under certain
conditions these transitions can lead to stable ground and excited states which
are not affected by the non inertial motion. The magnitude of the Unruh effect
is not altered by multi-level effects. Both the spontaneous excitation rates
and the Lamb shift are not within the range of measurability.Comment: 9 Pages, late
Anomalous fluctuations of the condensate in interacting Bose gases
We find that the fluctuations of the condensate in a weakly interacting Bose
gas confined in a box of volume follow the law . This anomalous behaviour arises from the occurrence of infrared
divergencies due to phonon excitations and holds also for strongly correlated
Bose superfluids. The analysis is extended to an interacting Bose gas confined
in a harmonic trap where the fluctuations are found to exhibit a similar
anomaly.Comment: 4 pages, RevTe
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