259 research outputs found
Ultraperipheral Collisions at RHIC and LHC
A brief introduction to the physics of ultraperipheral collisions at collider
energies is given. Photon-hadron (proton/ nucleus) and photon-photon
interactions can be studied in a hitherto unexplored energy regime.Comment: 3 pages, 2 figures, Proceedings of PHOTON 2007, Paris 9-13 July 2007,
to be published in Nucl. Phys. B (Proceedings Supplements
A Realistic Solvable Model for the Coulomb Dissociation of Neutron Halo Nuclei
As a model of a neutron halo nucleus we consider a neutron bound to an inert
core by a zero range force. We study the breakup of this simple nucleus in the
Coulomb field of a target nucleus. In the post-form DWBA (or, in our simple
model CWBA (``Coulomb Wave Born Approximation'')) an analytic solution for the
T-matrix is known. We study limiting cases of this T-matrix. As it should be,
we recover the Born approximation for weak Coulomb fields (i.e., for the
relevant Coulomb parameters much smaller than 1). For strong Coulomb fields,
high beam energies, and scattering to the forward region we find a result which
is very similar to the Born result. It is only modified by a relative phase
(close to 0) between the two terms and a prefactor (close to 1). A similar
situation exists for bremsstrahlung emission. This formula can be related to
the first order semiclassical treatment of the electromagnetic dissociation.
Since our CWBA model contains the electromagnetic interaction between the core
and the target nucleus to all orders, this means that higher order effects
(including postacceleration effects) are small in the case of high beam
energies and forward scattering. Our model also predicts a scaling behavior of
the differential cross section, that is, different systems (with different
binding energies, beam energies and scattering angles) show the same dependence
on two variables x and y.Comment: to appear in the Proceedings of ENAM2001, 3rd Internation Conference
on Exotic Nuclei and Atomic Masse
Single-Photon Switch based on Rydberg Blockade
All-optical switching is a technique in which a gate light pulse changes the
transmission of a target light pulse without the detour via electronic signal
processing. We take this to the quantum regime, where the incoming gate light
pulse contains only one photon on average. The gate pulse is stored as a
Rydberg excitation in an ultracold atomic gas using electromagnetically induced
transparency. Rydberg blockade suppresses the transmission of the subsequent
target pulse. Finally, the stored gate photon can be retrieved. A retrieved
photon heralds successful storage. The corresponding postselected subensemble
shows an extinction of 0.05. The single-photon switch offers many interesting
perspectives ranging from quantum communication to quantum information
processing
Ultraperipheral Collisions
Ultraperipheral collisions at heavy ion colliders use the strong Coulomb
fields surrounding the ions to study photon-photon and photon-hadron processes
at high energy. A number of processes of interest are discussed here.Comment: 12 pages, Talk presented at "Physics at LHC", Vienna, Austria, July
13-17, 2004. To be published in Czechoslovak Journal of Physic
Transverse momentum distribution of vector mesons produced in ultraperipheral relativistic heavy ion collisions
We study the transverse momentum distribution of vector mesons produced in
ultraperipheral relativistic heavy ion collisions (UPCs). In UPCs there is no
strong interaction between the nuclei and the vector mesons are produced in
photon-nucleus collisions where the (quasireal) photon is emitted from the
other nucleus. Exchanging the role of both ions leads to interference effects.
A detailed study of the transverse momentum distribution which is determined by
the transverse momentum of the emitted photon, the production process on the
target and the interference effect is done. We study the total unrestricted
cross section and those, where an additional electromagnetic excitation of one
or both of the ions takes place in addition to the vector meson production, in
the latter case small impact parameters are emphasized.Comment: 12 pages, REVTeX manuscrip
Production of Low Mass Electron Pairs Due to the Photon-Photon Mechanism in Central Collisions
We calculate the probability for dilepton production in central relativistic
heavy ion collisions due to the gamma-gamma mechanism. This is a potential
background to more interesting mechanisms. We find that this mechanism is
negligible in the CERES experiments. Generally, the contribution due to this
mechanism is small in the central region, while it can be large for small
invariant masses and forward or backward rapidities. A simple formula based on
the equivalent photon approximation and applications to a possible scenario at
RHIC are also given.Comment: 10 pages REVTeX, 5 Figures, for related work see
http://quasar.physik.unibas.ch/~hencken
Single-Photon Transistor Using a F\"orster Resonance
An all-optical transistor is a device in which a gate light pulse switches
the transmission of a target light pulse with a gain above unity. The gain
quantifies the change of the transmitted target photon number per incoming gate
photon. We study the quantum limit of one incoming gate photon and observe a
gain of 20. The gate pulse is stored as a Rydberg excitation in an ultracold
gas. The transmission of the subsequent target pulse is suppressed by Rydberg
blockade which is enhanced by a F\"orster resonance. The detected target
photons reveal in a single shot with a fidelity above 0.86 whether a Rydberg
excitation was created during the gate pulse. The gain offers the possibility
to distribute the transistor output to the inputs of many transistors, thus
making complex computational tasks possible
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