2,210 research outputs found
Ultimate parameters of the photon collider at the ILC
At linear colliders, the e+e- luminosity is limited by beam-collision
effects, which determine the required emittances of beams in damping rings
(DRs). While in gamma-gamma collisions at the photon collider, these effects
are absent, and so smaller emittances are desirable. In present damping rings
designs, nominal DR parameters correspond to those required for e+e-
collisions. In this note, I would like to stress once again that as soon as we
plan the photon-collider mode of ILC operation, the damping-ring emittances are
dictated by the photon-collider requirements--namely, they should be as small
as possible. This can be achieved by adding more wigglers to the DRs; the
incremental cost is easily justified by a considerable potential improvement of
the gamma-gamma luminosity. No expert analysis exists as of yet, but it seems
realistic to obtain a factor five increase of the gamma-gamma luminosity
compared to the ``nominal'' DR design.Comment: Talk at LCWS06, Bangalore, India, March 2006, to be published in
Indian Journal of Physics, 5 pp, Latex, 1 .eps figur
Relativistic mask method for electron momentum distributions after ionization of hydrogen-like ions in strong laser fields
Wavefunction-splitting or mask method, widely used in the non-relativistic
calculations of the photoelectron angular distributions, is extended to the
relativistic domain within the dipole approximation. Since the closed-form
expressions for the relativistic Volkov states are not available within the
dipole approximation, we build such states numerically solving a single
second-order differential equation. We calculate the photoelectron energy
spectra and angular distributions for highly charged ions under different
ionization regimes with both the direct and the relativistic mask methods. We
show that the relativistic mask method works very well and reproduces the
electron energy and angular distributions calculated by the direct method in
the energy range where both methods can be used. On the other hand, the
relativistic mask method can be applied for longer laser pulses and/or higher
photoelectron energies where the direct method may have difficulties
Restriction on the energy and luminosity of e+e- storage rings due to beamstrahlung
The role of beamstrahlung in high-energy e+e- storage-ring colliders (SRCs)
is examined. Particle loss due to the emission of single energetic
beamstrahlung photons is shown to impose a fundamental limit on SRC
luminosities at energies 2E_0 >~ 140 GeV for head-on collisions and 2E_0 >~ 40
GeV for crab-waist collisions. With beamstrahlung taken into account, we
explore the viability of SRCs in the E_0=240-500 GeV range, which is of
interest in the precision study of the Higgs boson. At 2E_0=240 GeV, SRCs are
found to be competitive with linear colliders; however, at 2E_0=400-500 GeV,
the attainable SRC luminosity would be a factor 15-25 smaller than desired.Comment: Latex, 5 pages. v2 differs only by minor changes is abstract and
introduction, one reference is added. v3 corresponds to the paper published
in PR
Full one-loop QCD and electroweak corrections to sfermion pair production in collisions
We have calculated the full one-loop electroweak (EW) and QCD corrections to
the third generation scalar-fermion pair production processes at an
electron-positron linear collider(LC) in the minimal supersymmetric standard
model (MSSM). We analyze the dependence of the radiative corrections on the
parameters such as the colliding energy and the SUSY
fundamental parameters , , , and so forth. The
numerical results show that the EW corrections to the squark-, stau-pair
production processes and QCD corrections to the squark-pair production
processes give substantial contributions in some parameter space. The EW
relative corrections to squark-pair production processes can be comparable with
QCD corrections at high energies. Therefore, these EW and QCD corrections
cannot be neglected in precise measurement of sfermion pair productions via
collision at future linear colliders.Comment: to be appeared in Phys. Rev.
High energy behaviour of gamma gamma to f f(bar) processes in SM and MSSM
We compute the leading logarithms electroweak contributions to gamma gamma to
f f(bar) processes in SM and MSSM. Several interesting properties are pointed
out, such as the importance of the angular dependent terms, of the Yukawa
terms, and especially of the dependence in the SUSY
contributions. These properties are complementary to those found in e+e- to f
f(bar). These radiative correction effects should be largely observable at
future high energy gamma gamma colliders. Polarized beams would bring
interesting checks of the structure of the one loop corrections. We finally
discuss the need for two-loop calculations and resummation.Comment: 22 pages and 12 figures. e-mail: [email protected]
Electron (positron) beam polarization by Compton scattering on circularly polarized laser photons
In a number of papers an attractive method of laser polarization of electrons
(positrons) at storage rings or linear colliders has been proposed. We show
that these suggestions are incorrect and based on errors in simulation of
multiple Compton scattering and in calculation of the Compton spin-flip cross
sections. We argue that the equilibrium polarization in this method is zero.Comment: 11 pages, LaTeX, talk at 9-th Intern. Workshop on Linear Colliders
(LC02), Feb. 4-8, 2002, SLAC, Stanford, US
Backward scattering of low-energy antiprotons by highly charged and neutral uranium: Coulomb glory
Collisions of antiprotons with He-, Ne-, Ni-like, bare, and neutral uranium
are studied theoretically for scattering angles close to 180 and
antiproton energies with the interval 100 eV -- 10 keV. We investigate the
Coulomb glory effect which is caused by a screening of the Coulomb potential of
the nucleus and results in a prominent maximum of the differential cross
section in the backward direction at some energies of the incident particle. We
found that for larger numbers of electrons in the ion the effect becomes more
pronounced and shifts to higher energies of the antiproton. On the other hand,
a maximum of the differential cross section in the backward direction can also
be found in the scattering of antiprotons on a bare uranium nucleus. The latter
case can be regarded as a manifestation of the screening property of the
vacuum-polarization potential in non-relativistic collisions of heavy
particles.Comment: 14 pages, 5 figure
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