402 research outputs found
Polarization Phenomena by Deuteron Fragmentation into Pions
The fragmentation of deuterons into pions emitted forward in the kinematic
region forbidden for free nucleon-nucleon collisions is analyzed. The inclusive
relativistic invariant spectrum of pions and the tensor analyzing power T_{20}
are investigated within the framework of an impulse approximation using
different kinds of the deuteron wave function. The influence of P-wave
inclusion in the deuteron wave function is studied, too. The invariant spectrum
is shown to be more sensitive to the amplitude of the process
than the tensor analyzing power T_{20}. It is shown that the inclusion of the
non-nucleon degrees of freedom in a deuteron results a satisfactory description
of experimental data about the inclusive pion spectrum and improves the
description of data about T_{20}. According to the experimental data, T_{20}
has the positive sign and very small values, less than 0.2, what contradicts to
the theoretical calculations ignoring these degrees of freedom.Comment: 18 pages, 8 eps figures, 1 picture - svjour.cls required; enlarged
new version with corrections and additional figure. The Abstract and the
section "Summary and outlook" have been also corrected. Final version to
appear in Eur.Phys.J. A. A talk given at the International Workshop
"Symmetries and Spin" (July 17-22, Prague, Czech Republic
Probing the deuteron structure at small N-N distances by cumulative pion production
The fragmentation of deuterons into pions emitted forward in the kinematic
region forbidden for free nucleon-nucleon collisions is analyzed. It is shown
that the inclusion of the non-nucleonic degrees of freedom in a deuteron
results in a satisfactory description of the data for the inclusive pion
spectrum and improves the description of the data about . According to
the data, has very small positive values, less than 0.2, which
contradicts the theoretical calculations ignoring these degrees of freedom.Comment: 3 pages, 2 postscript figures; to appear in the proceedings of
Conference on Quarks and Nuclear Physics (QNP 2002), Julich, Germany, 9-14
Jun 200
Tensor analyzing power Ayy in deuteron inclusive breakup at large Pt and spin structure of deuteron at short internucleonic distances
The Ayy data for deuteron inclusive breakup off hydrogen and carbon at a
deuteron momentum of 9.0 GeV/c and large Pt of emitted protons are presented.
The large values of Ayy independent of the target mass reflect the sensitivity
of the data to the deuteron spin structure. The data obtained at fixed and
plotted versus Pt clearly demonstrate the dependence of the deuteron spin
structure at short internucleonic distances on two variables. The data are
compared with the calculations using Paris, CD-Bonn and Karmanov's deuteron
wave functions.Comment: 4 pages, 2 figures, talk given at the SPIN2004 Conf., 10-16 Oct.
2004, Triest, Ital
Polarization control proposal for Shanghai deep ultraviolet free electron laser
In this paper, a fully coherent radiation option with controllable
polarization is proposed for Shanghai deep ultraviolet free electron laser
(FEL) test facility. Intensive start-to-end simulation suggests that, the two
crossed planar undulators which generate the horizontal and vertical linear
polarized FEL respectively, should be placed as close as possible for avoiding
the polarization performance degradation of the final combined FEL radiation.
With the existence of the phase-shifter between the two crossed radiators,
Fourier-Transform-Limited output radiation with 100 nJ order pulse energy, 5 ps
full pulse length and circular polarization degree above 90% could be achieved.Comment: 9 pages, 5 figures, 1 tabl
Type II Radio Emission and Solar Particle Observations
The 28 October 2003 flare gave us the unique opportunity to compare the
acceleration time of high-energy protons with the escaping time of those
particles which have been measured onboard spacecraft and by neutron monitors
network as GLE event. High-energy emission time scale and shock wave height and
velocity time dependencies were also studied.Comment: International Journal of Modern Physics A, Volume 20, Issue 29, pp.
6705-6707 (2005
New insights into electron spin dynamics in the presence of correlated noise
The changes of the spin depolarization length in zinc-blende semiconductors
when an external component of correlated noise is added to a static driving
electric field are analyzed for different values of field strength, noise
amplitude and correlation time. Electron dynamics is simulated by a Monte Carlo
procedure which keeps into account all the possible scattering phenomena of the
hot electrons in the medium and includes the evolution of spin polarization.
Spin depolarization is studied by examinating the decay of the initial spin
polarization of the conduction electrons through the D'yakonov-Perel process,
the only relevant relaxation mechanism in III-V crystals. Our results show
that, for electric field amplitude lower than the Gunn field, the dephasing
length shortens with the increasing of the noise intensity. Moreover, a
nonmonotonic behavior of spin depolarization length with the noise correlation
time is found, characterized by a maximum variation for values of noise
correlation time comparable with the dephasing time. Instead, in high field
conditions, we find that, critically depending on the noise correlation time,
external fluctuations can positively affect the relaxation length. The
influence of the inclusion of the electron-electron scattering mechanism is
also shown and discussed.Comment: Published on "Journal of Physics: Condensed Matter" as "Fast Track
Communications", 11 pages, 9 figure
Analysis of the rotation period of asteroids (1865) Cerberus, (2100) Ra-Shalom, and (3103) Eger - search for the YORP effect
The spin state of small asteroids can change on a long timescale by the
Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect, the net torque that arises
from anisotropically scattered sunlight and proper thermal radiation from an
irregularly-shaped asteroid. The secular change in the rotation period caused
by the YORP effect can be detected by analysis of asteroid photometric
lightcurves. We analyzed photometric lightcurves of near-Earth asteroids (1865)
Cerberus, (2100) Ra-Shalom, and (3103) Eger with the aim to detect possible
deviations from the constant rotation caused by the YORP effect. We carried out
new photometric observations of the three asteroids, combined the new
lightcurves with archived data, and used the lightcurve inversion method to
model the asteroid shape, pole direction, and rotation rate. The YORP effect
was modeled as a linear change in the rotation rate in time d\omega /dt. Values
of d\omega/ dt derived from observations were compared with the values
predicted by theory. We derived physical models for all three asteroids. We had
to model Eger as a nonconvex body because the convex model failed to fit the
lightcurves observed at high phase angles. We probably detected the
acceleration of the rotation rate of Eger d\omega / dt = (1.4 +/- 0.6) x
10^{-8} rad/d (3\sigma error), which corresponds to a decrease in the rotation
period by 4.2 ms/yr. The photometry of Cerberus and Ra-Shalom was consistent
with a constant-period model, and no secular change in the spin rate was
detected. We could only constrain maximum values of |d\omega / dt| < 8 x
10^{-9} rad/d for Cerberus, and |d\omega / dt| < 3 x 10^{-8} rad/d for
Ra-Shalom
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