375 research outputs found
Method of functional integration in the problem of line width of parametric X-ray relativistic electron radiation in a crystal
The coherent and non-coherent scattering effects on "backward" parametric
X-ray radiation by relativistic electrons in a crystal on the basis of the
method of functional integration is investigated. A comparison of contributions
of these effects to parametric X-ray radiation line width has been considered.
It is shown that in a number of cases the major contribution to the line width
of parametric X-ray radiation is made by non-coherent multiple scattering.Comment: 7 pages, LaTeX2e forma
LPM effect as the origin of the jet fragmentation scaling in heavy ion collisions
We address a recent puzzling result from the LHC: the jet fragmentation
functions measured in and collisions appear very similar in spite
of a large medium-induced energy loss (we will call this "jet fragmentation
scaling", JFS). To model the real-time non-perturbative effects in the
propagation of a high energy jet through the strongly coupled QCD matter, we
adopt an effective dimensionally reduced description in terms of the
quasi-Abelian Schwinger theory. This theory is exactly soluble at any value of
the coupling and shares with QCD the properties of dynamical generation of
"mesons" with a finite mass and the screening of "quark" charge that are
crucial for describing the transition of the jet into hadrons. We find that
this approach describes quite well the vacuum jet fragmentation in
annihilation at at jet energies in the range of the LHC heavy ion
measurements ( is the ratio of hadron and jet momenta). In QCD medium, we
find that the JFS is reproduced if the mean free path of the jet is
short, fm, which is in accord with the small shear viscosity
inferred from the measurements of the collective flow. The JFS holds since at
short mean free path the quantum interference (analogous to the
Landau-Pomeranchuk-Migdal effect in QED) causes the produced mesons to have low
momenta , where GeV is the typical meson mass.
Meanwhile the induced jet energy loss at short mean free path is much larger
than naively expected in string models.Comment: 4 pages, 4 figure
Measurements of Compton Scattered Transition Radiation at High Lorentz Factors
X-ray transition radiation can be used to measure the Lorentz factor of
relativistic particles. Standard transition radiation detectors (TRDs)
typically incorporate thin plastic foil radiators and gas-filled x-ray
detectors, and are sensitive up to \gamma ~ 10^4. To reach higher Lorentz
factors (up to \gamma ~ 10^5), thicker, denser radiators can be used, which
consequently produce x-rays of harder energies (>100 keV). At these energies,
scintillator detectors are more efficient in detecting the hard x-rays, and
Compton scattering of the x-rays out of the path of the particle becomes an
important effect. The Compton scattering can be utilized to separate the
transition radiation from the ionization background spatially. The use of
conducting metal foils is predicted to yield enhanced signals compared to
standard nonconducting plastic foils of the same dimensions. We have designed
and built a Compton Scatter TRD optimized for high Lorentz factors and exposed
it to high energy electrons at the CERN SPS. We present the results of the
accelerator tests and comparisons to simulations, demonstrating 1) the
effectiveness of the Compton Scatter TRD approach; 2) the performance of
conducting aluminum foils; and 3) the ability of a TRD to measure energies
approximately an order of magnitude higher than previously used in very high
energy cosmic ray studies.Comment: 10 pages, 4 figures, To be published in NI
Spectrum of Radiation from Rough Surfaces
Radiation from a charged particle travelling parallel to a rough surface has
been considered. Spectral-angular intensity is calculated in the weak
scattering regime. It is shown that the main contribution to the radiation
intensity is determined by the multiple scattering of polaritons induced by a
charge on the surface. Multiple scattering effects lead to strong frequency
dependence of radiation intensity. Possible applications in beam and surface
diagnostics are discussed.Comment: submitted to Europhys.Let
Synchrotron radiation contributions to optical diffraction radiation measurements
If we try to measure the backward optical diffraction radiation (BODR) of
high energy electrons from a conductive slit or a semi infinitive plate, the
electron beam will pass thru the bending or steering magnets or magnet lenses
before striking the target. The synchrotron radiation (SR) from these magnets
can obscure the BODR measurements. An analysis of the properties of SR from
these magnets is in this paper presented. A model based on the modified Lenar
Wikherd potentials was created, and the SR angular distribution from
relativistic electrons in bending and steering magnets for different conditions
of radiation in the optical region was calculated. The analysis shows, that for
the conditions of the KEK ATF extraction line, the intensity of SR exceeds that
of the backward optical transition radiation (BOTR) from the conducting
targets, and it is much lager than the intensity of the BODR. The SR intensity
from the steering magnets depends on its tuning and may be comparable to BOTR.
Thus, these results it is seen, that the problem of separation of the BODR and
SR in the BODR measurements is important. Two methods resolving of this problem
is in this article suggested
Diffraction Radiation Diagnostics for Moderate to High Energy Charged Particle Beams
Diffraction radiation (DR) is produced when a charged particle passes through
an aperture or near a discontinuity in the media in which it is traveling. DR
is closely related to transition radiation (TR), which is produced when a
charged particle traverses the boundary between media with different dielectric
constants. In contrast to TR, which is now extensively used for beam diagnostic
purposes, the potential of DR as a non-interceptive, multi-parameter beam
diagnostic remains largely undeveloped. For diagnostic measurements it is
useful to observe backward reflected DR from an circular aperture or slit
inclined with respect to the beam velocity. However, up to now, well founded
equations for the spectral-angular intensities of backward DR from such
apertures have not been available. We present a new derivation of the spectral
angular intensity of backward DR produced from an inclined slit for two
orientations of the slit axis, i.e. perpendicular and parallel to the plane of
incidence. Our mathematical approach is generally applicable to any geometry
and simpler than the Wiener Hofp method previously used to calculate DR from
single knife edges. Our results for the slit are applied to the measurement of
orthogonal beam size and divergence components. We discuss the problem of
separating the simultaneous effects of these beam parameters on the angular
distribution of DR and provide solutions to this difficulty. These incude using
the horizontal and vertical polarization components of the radiation from a
single slit and interferences from two inclined slits. Examples of DR
diagnostics for a 500 MeV beam are presented and the current limitations to the
technique are discussed.Comment: 32 pages,including 14 figures; submitted to NIM
Compton Scattered Transition Radiation from Very High Energy Particles
X-ray transition radiation can be used to measure the Lorentz factor of
relativistic particles. At energies approaching gamma = E/mc^2 = 10^5,
transition radiation detectors (TRDs) can be optimized by using thick (sim 5 -
10 mil) foils with large (5-10 mm) spacings. This implies X-ray energies >100
keV and the use of scintillators as the X-ray detectors. Compton scattering of
the X-rays out of the particle beam then becomes an important effect. We
discuss the design of very high energy detectors, the use of metal radiator
foils rather than the standard plastic foils, inorganic scintillators for
detecting Compton scattered transition radiation, and the application to the
ACCESS cosmic ray experiment.Comment: To be published, Astroparticle Physic
Resonant Diffraction Radiation and Smith-Purcell Effect
An approach has been developed where the Smith-Purcell radiation (SPR), i.e.
emission of electrons moving close to a periodic structure, is treated as the
resonant diffraction radiation. Simple formulas have been designed for the SPR
intensity for a grating having perfectly conducting strips spaced by a vacuum
gap. The results have been compared with those obtained via other techniques.
It has been shown that the intensity of radiation for the said gratings for a
relativistic case sufficiently exceeds the SPR intensity for the grating made
up by a periodically deformed continuous surface.Comment: 9 pages, LATEX, 3 Postscript figures, uses epsf.sty, submitted to
Phys.Letters
Quantum theory of transition radiation and transition pair creation
Theory of the transition radiation and the transition pair creation is
developed in the frame of QED. The spectral-angular distributions of
probability of the transition radiation and of the transition pair creation are
found. The total energy losses of and the total probability of pair creation
are calculated and analyzed. Features of radiation and pair creation processes
in a superdence medium (typical for white dwarfs) are discussed.Comment: LaTeX, 12 pages, 3 eps figure
Experimental Research of the Diffraction and Vavilov-Cherenkov Radiation Generation in a Teflon Target
Geometry of Vavilov-Cherekov (VChR) radiation when an electron moves close to
a dielectric target is in analogy to diffraction radiation (DR) geometry. In
this case we may expect DR generation from the upstream face of the target
besides that VChR. The joint observation of these booth types of radiation is
very interesting from the pseudo-photon viewpoint, which is applicable for
relativistic electrons. Unexpected results obtained in our experiment insist on
reflection about nature both DR and VChR. The experiment was performed on the
relativistic electron beam of the microtron of Tomsk Polytechnic University.Comment: This article will be published in Journal of Physic
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