7,799 research outputs found
Collapses and revivals of stored orbital angular momentum of light in a cold atomic ensemble
We report on the storage of orbital angular momentum of light in a cold
ensemble of cesium atoms. We employ Bragg diffraction to retrieve the stored
optical information impressed into the atomic coherence by the incident light
fields. The stored information can be manipulated by an applied magnetic field
and we were able to observe collapses and revivals due to the rotation of the
stored atomic Zeeman coherence for times longer than 15 .Comment: Submitted to Physical Review
Dynamics of a stored Zeeman coherence grating in an external magnetic field
We investigate the evolution of a Zeeman coherence grating induced in a cold
atomic cesium sample in the presence of an external magnetic field. The
gratings are created in a three-beam light storage configuration using two
quasi-collinear writing laser pulses and reading with a counterpropagating
pulse after a variable time delay. The phase conjugated pulse arising from the
atomic sample is monitored. Collapses and revivals of the retrieved pulse are
observed for different polarizations of the laser beams and for different
directions of the applied magnetic field. While magnetic field inhomogeneities
are responsible for the decay of the coherent atomic response, a five-fold
increase in the coherence decay time, with respect to no applied magnetic
field, is obtained for an appropriate choice of the direction of the applied
magnetic field. A simplified theoretical model illustrates the role of the
magnetic field mean and its inhomogeneity on the collective atomic response.Comment: To appear in J. Phys.
Study of boundary-layer transition using transonic-cone preston tube data
The laminar boundary layer on a 10 degree cone in a transonic wind tunnel was studied. The inviscid flow and boundary layer development were simulated by computer programs. The effects of pitch and yaw angles on the boundary layer were examined. Preston-tube data, taken on the boundary-layer-transition cone in the NASA Ames 11 ft transonic wind tunnel, were used to develope a correlation which relates the measurements to theoretical values of laminar skin friction. The recommended correlation is based on a compressible form of the classical law-of-the-wall. The computer codes successfully simulates the laminar boundary layer for near-zero pitch and yaw angles. However, in cases of significant pitch and/or yaw angles, the flow is three dimensional and the boundary layer computer code used here cannot provide a satisfactory model. The skin-friction correlation is thought to be valid for body geometries other than cones
Double Higgs production at TeV Colliders in the Minimal Supersymmetric Standard Model
The reconstruction of the Higgs potential in the Minimal Supersymmetric
Standard Model (MSSM) requires the measurement of the trilinear Higgs
self-couplings. The `double Higgs production' subgroup has been investigating
the possibility of detecting signatures of processes carrying a dependence on
these vertices at the Large Hadron Collider (LHC) and future Linear Colliders
(LCs). As reference reactions, we have chosen and ,
respectively, where is the lightest of the MSSM Higgs bosons. In both
cases, the interaction is involved. For , the two reactions are
resonant in the mode, providing cross sections which are detectable
at both accelerators and strongly sensitive to the strength of the trilinear
coupling involved. We explore this mass regime of the MSSM in the decay channel, also accounting for irreducible background effects.Comment: LaTeX, 23 pages, 13 PostScript figures (contribution to the Summary
Report of the Higgs WG, Workshop `Physics at TeV Colliders', Les Houches,
France, 8-18 June 1999): some modifications to the bibliograph
Multiple Z' -> t-tbar signals in a 4D Composite Higgs Model
We study the production of top-antitop pairs at the Large Hadron Collider as
a testbed for discovering heavy Z' bosons belonging to a composite Higgs model,
as, in this scenario, such new gauge interaction states are sizeably coupled to
the third generation quarks of the Standard Model. We study their possible
appearance in cross section as well as (charge and spin) asymmetry
distributions. Our calculations are performed in the minimal four-dimensional
formulation of such a scenario, namely the 4-Dimensional Composite Higgs Model
(4DCHM), which embeds five new s. We pay particular attention to the case
of nearly degenerate resonances, highlighting the conditions under which these
are separable in the aforementioned observables. We also discuss the impact of
the intrinsic width of the new resonances onto the event rates and various
distributions. We confirm that the 14 TeV stage of the LHC will enable one to
detect two such states, assuming standard detector performance and machine
luminosity. A mapping of the discovery potential of the LHC of these new gauge
bosons is given. Finally, from the latter, several benchmarks are extracted
which are amenable to experimental investigation.Comment: 30 pages, 3 figures. Text and figures updated to match published
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