327 research outputs found
Observation of Scaling Violations in Scaled Momentum Distributions at HERA
Charged particle production has been measured in deep inelastic scattering
(DIS) events over a large range of and using the ZEUS detector. The
evolution of the scaled momentum, , with in the range 10 to 1280
, has been investigated in the current fragmentation region of the Breit
frame. The results show clear evidence, in a single experiment, for scaling
violations in scaled momenta as a function of .Comment: 21 pages including 4 figures, to be published in Physics Letters B.
Two references adde
Level density of a Fermi gas: average growth and fluctuations
We compute the level density of a two--component Fermi gas as a function of
the number of particles, angular momentum and excitation energy. The result
includes smooth low--energy corrections to the leading Bethe term (connected to
a generalization of the partition problem and Hardy--Ramanujan formula) plus
oscillatory corrections that describe shell effects. When applied to nuclear
level densities, the theory provides a unified formulation valid from
low--lying states up to levels entering the continuum. The comparison with
experimental data from neutron resonances gives excellent results.Comment: 4 pages, 1 figur
Attosecond gamma-ray pulses via nonlinear Compton scattering in the radiation dominated regime
The feasibility of generation of bright ultrashort gamma-ray pulses is
demonstrated in the interaction of a relativistic electron bunch with a
counterpropagating tightly-focused superstrong laser beam in the radiation
dominated regime. The Compton scattering spectra of gamma-radiation are
investigated using a semiclassical description for the electron dynamics in the
laser field and a quantum electrodynamical description for the photon emission.
We demonstrate the feasibility of ultrashort gamma-ray bursts of hundreds of
attoseconds and of dozens of megaelectronvolt photon energies in the
near-backwards direction of the initial electron motion. The tightly focused
laser field structure and radiation reaction are shown to be responsible for
such short gamma-ray bursts which are independent of the durations of the
electron bunch and of the laser pulse. The results are measurable with the
laser technology available in a near-future
Coulomb corrections to density and temperature in heavy ion collisions
A recently proposed method, based on quadrupole and multiplicity fluctuations
in heavy ion collisions, is modified in order to take into account distortions
due to the Coulomb field. The classical and quantum limits for fermions are
discussed. In the classical case we find that the temperature determined from
and , after the Coulomb correction, are very similar to those
obtained from neutrons within the Constrained Molecular Dynamics (CoMD)
approach. In the quantum case, the proton temperature becomes very similar to
neutron's, while densities are not sensitive to the Coulomb corrections
Fitting theories of nuclear binding energies
In developing theories of nuclear binding energy such as density-functional
theory, the effort required to make a fit can be daunting due to the large
number of parameters that may be in the theory and the large number of nuclei
in the mass table. For theories based on the Skyrme interaction, the effort can
be reduced considerably by using the singular value decomposition to reduce the
size of the parameter space. We find that the sensitive parameters define a
space of dimension four or so, and within this space a linear refit is adequate
for a number of Skyrme parameters sets from the literature. We do not find
marked differences in the quality of the fit between the SLy4, the Bky4 and SkP
parameter sets. The r.m.s. residual error in even-even nuclei is about 1.5 MeV,
half the value of the liquid drop model. We also discuss an alternative norm
for evaluating mass fits, the Chebyshev norm. It focuses attention on the cases
with the largest discrepancies between theory and experiment. We show how it
works with the liquid drop model and make some applications to models based on
Skyrme energy functionals. The Chebyshev norm seems to be more sensitive to new
experimental data than the root-mean-square norm. The method also has the
advantage that candidate improvements to the theories can be assessed with
computations on smaller sets of nuclei.Comment: 17 pages and 4 figures--version encorporates referee's comment
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