679 research outputs found
A Future Linear Collider with polarised beams: Searches for New Physics
There exists a world--wide consensus for a future Linear Collider in
the energy range between GeV as the next large facility in
HEP. The Linear Collider has a large physics potential for the discovery of new
physics beyond the Standard Model and for precision studies of the Standard
Model itself. It is well suited to complement and extend the physics program of
the LHC. The use of polarised beams at a Linear Collider will be one of the
powerful tools. In this paper some highlights of searches for physics beyond
the Standard Model at a future Linear Collider with polarised and
beams are summarised.Comment: 15 pages, 10 eps figures, Invited plenary talk given at 15th
International Spin Physics Symposium, September 2002, BNL, Brookhaven, US
Physics aspects of polarized e+ at the linear collider
Polarized e- and e+ at the International Linear Collider play an important
role for discovering physics beyond the Standard Model and for precisely
unravelling the structure of the underlying physics. The physics programme at
the first energy stage at sqrt{s}=500 GeV benefits strongly from the
polarization of both beams. But also at 1 TeV as well as at a possible
multi-TeV design of a linear collider, CLIC, the physics output is greatly
enriched by beam polarization. An overview is given of the impact of providing
polarized e+ at the linear collider in addition to polarized e- for physics
studies in top, Higgs, supersymmetry and further models of physics beyond the
Standard Model.Comment: 14 pages, 16 eps figures Talk given at the Polarized Positrons
Workshop `POSIPOL', CERN, 26-28 April 200
News from polarized e- and e+ at the ILC
The proposed International Linear Collider (ILC) is well-suited for
discovering physics beyond the Standard Model and for precisely unravelling the
structure of the underlying physics. The physics return of the ILC can be
maximized by the use of polarized beams, in particular the simultaneous
polarization of the e- and the e+ beam. Ongoing physics studies are accompanied
by active R&D on the machine part for generating polarized beams and for
measuring the polarization with high precision at the ILC. Some new results on
the physics case and on the technical aspects of the polarization of both beams
are briefly summarized.Comment: 6 pages, 12 eps figures, style files; Contribution to '2005
International Linear Collider Workshop -Stanford, U.S.A.
Prototype for an Undulator-based Source for Polarised Positrons: International Polarised Positron Collaboration: Project E-166
The full exploitation of the physics potential of a future Linear Collider
requires the development of polarised positron beams. A very promising scheme
for the technical realisation is the use of helical undulators, generating
circular polarised photons of several MeV which are then converted in a thin
target to longitudinally polarised positrons. The experiment E-166 tests this
scheme. It uses the low-emittance 50-GeV electron beam at the Final Focus Test
Beam (FFTB) at SLAC, passing through a 1 meter-long helical undulator. The flux
and polarisation of the undulator photons as well as the properties of the
positrons will be measured and will be compared with simulations.Comment: 3 pages, 5 postscript figures, epj style, talk given at the EPS
conference, Aachen, Germany, July 200
LHC/ILC Interplay in SUSY Searches
Combined analyses at the Large Hadron Collider and at the International
Linear Collider are important to reveal precisely the new physics model as, for
instance, supersymmetry. Examples are presented where ILC results as input for
LHC analyses could be crucial for the identification of signals as well as of
the underlying model. The synergy of both colliders leads also to rather
accurate SUSY parameter determination and powerful mass constraints even if the
scalar particles have masses in the multi-TeV range.Comment: 5 pages, contribution to the proceedings of EPS0
Euclidean mirrors: enhanced vacuum decay from reflected instantons
We study the tunneling of virtual matter-antimatter pairs from the quantum
vacuum in the presence of a spatially uniform, time-dependent electric
background composed of a strong, slow field superimposed with a weak, rapid
field. After analytic continuation to Euclidean spacetime, we obtain from the
instanton equations two critical points. While one of them is the closing point
of the instanton path, the other serves as an Euclidean mirror which reflects
and squeezes the instanton. It is this reflection and shrinking which is
responsible for an enormous enhancement of the vacuum pair production rate. We
discuss how important features of two different mechanisms can be analysed and
understood via such a rotation in the complex plane. a) Consistent with
previous studies, we first discuss the standard assisted mechanism with a
static strong field and certain weak fields with a distinct pole structure in
order to show that the reflection takes place exactly at the poles. We also
discuss the effect of possible sub-cycle structures. We extend this reflection
picture then to weak fields which have no poles present and illustrate the
effective reflections with explicit examples. An additional field strength
dependence for the rate occurs in such cases. We analytically compute the
characteristic threshold for the assisted mechanism given by the critical
combined Keldysh parameter. We discuss significant differences between these
two types of fields. For various backgrounds, we present the contributing
instantons and perform analytical computations for the corresponding rates
treating both fields nonperturbatively. b) In addition, we also study the case
with a nonstatic strong field which gives rise to the assisted dynamical
mechanism. For different strong field profiles we investigate the impact on the
critical combined Keldysh parameter. [...]Comment: 54 pages, 23 figures, revised, restructured to improve readability,
matches journal versio
Nonlinear lepton-photon interactions in external background fields
Nonlinear phenomena of lepton-photon interactions in external backgrounds
with a generalised periodic plane-wave geometry are studied. We discuss
nonlinear Compton scattering in head-on lepton-photon collisions extended
properly to beyond the soft-photon regime. In addition, our results are applied
to stimulated lepton-antilepton pair production in photon collisions with
unrestricted energies. Derivations are considered semi-classically based on
unperturbed fermionic Volkov representations encoding the full interaction with
the background field. Closed expressions for total probabilities considering
S-matrix elements have been derived. The general formula is applied to Compton
scattering by an electron propagating in an external laser-like background. We
obtain additive contributions in the extended unconstrained result which turns
out to be stringently required in the highly nonlinear regime. A detailed
comparison of contributing harmonics is discussed for various field parameters.Comment: 39 pages, 8 figures, minor changes in introduction, references added,
a few misprints foun
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