353 research outputs found
Decay theory of double giant resonances
The decay theory of double giant resonances incorporating fluctuation
contributions of the Brink-Axel type is developed. The gamma and neutron
emission decay of Double Giant Dipole Resonances (DGDR) in 208Pb is discussed
in connection with a recent measurement.Comment: 5 pages, Late
Multiphonon and ``hot''-phonon Isovector Electric-Dipole Excitations
We argue that a substantial increase in the cross section for Coulomb
excitation in the region of the Double Giant Dipole Resonance should be
expected from Coulomb excitation of excited states involved in the spreading of
the one-phonon resonance, in a manifestation of the Brink-Axel phenomenon. This
generates an additional fluctuating amplitude and a corresponding new term to
be added incoherently to the usual cross-section. The appropriate extension of
an applicable reaction calculation is considered in order to estimate this
effect.Comment: 6 pages, Latex, 1 figure available on reques
SU(2,1) Dynamics of Multiple Giant Dipole Resonance Coulomb Excitation
We construct a three-dimensional analytically soluble model of the nonlinear
effects in Coulomb excitation of multiphonon Giant Dipole Resonances (GDR)
based on the SU(2,1) algebra. The full 3-dimensional model predicts further
enhancement of the Double GDR (DGDR) cross sections at high bombarding
energies. Enhancement factors for DGDR measured in thirteen different processes
with various projectiles and targets at different bombarding energies are well
reproduced with the same value of the nonlinearity parameter with the exception
of the anomalous case of Xe which requires a larger value.Comment: 10 pages, 3 Postscript figures, late
Equilibrium and stability properties of a coupled two-component Bose-Einstein condensate
The equilibrium and stability properties of a coupled two-component BEC is
studied using a variational method and the one-dimensional model of Williams
and collaborators. The variational parameters are the population fraction,
translation and scaling transformation of the condensate densities, assumed to
have a Gaussian shape. We study the equilibrium and stability properties as a
function of the strength of the laser field and the traps displacement. We find
many branches of equilibrium configurations, with a host of critical points. In
all cases, the signature of the onset of criticality is the collapse of a
normal mode which is a linear combination of the out of phase translation and
an in phase breathing oscillation of the condensate densities. Our calculations
also indicate that we have symmetry breaking effects when the traps are not
displacedComment: 13 pages,3 figure
Theory of Multiphonon Excitation in Heavy-Ion Collisions
We study the effects of channel coupling in the excitation dynamics of giant
resonances in relativistic heavy ions collisions. For this purpose, we use a
semiclassical approximation to the Coupled-Channels problem and separate the
Coulomb and the nuclear parts of the coupling into their main multipole
components. In order to assess the importance of multi-step processes, we
neglect the resonance widths and solve the set of coupled equations exactly.
Finite widths are then considered. In this case, we handle the coupling of the
ground state with the dominant Giant Dipole Resonance exactly and study the
excitation of the remaining resonances within the Coupled-Channels Born
Approximation. A comparison with recent experimental data is made.Comment: 29 pages, 7 Postscript figures available upon reques
Anomalous anapole moment of an exotic nucleus
Using the information on the nuclear structure of exotic neutron-rich halo
nucleus Be, we evaluate the parity violating anapole moment in its
ground state. The resulting value Be) is fifteen times
bigger than the typical value of the anapole moment of a normal nucleus of the
same mass, and in fact exceeds by few times anapole moments of any known
neutron-odd nuclei (e.g., kappa(^{11}Be) > 2|\kappa(^{207}Pb)|. It is also few
times bigger than the neutral current contribution to the lepton-nucleus
interaction.Comment: 12 pages, 2 figure
Maximal surface group representations in isometry groups of classical Hermitian symmetric spaces
Higgs bundles and non-abelian Hodge theory provide holomorphic methods with
which to study the moduli spaces of surface group representations in a
reductive Lie group G. In this paper we survey the case in which G is the
isometry group of a classical Hermitian symmetric space of non-compact type.
Using Morse theory on the moduli spaces of Higgs bundles, we compute the number
of connected components of the moduli space of representations with maximal
Toledo invariant.Comment: v2: added due credits to the work of Burger, Iozzi and Wienhard. v3:
corrected count of connected components for G=SU(p,q) (p \neq q); added due
credits to the work of Xia and Markman-Xia; minor corrections and
clarifications. 31 page
Pion, kaon, proton and anti-proton transverse momentum distributions from p+p and d+Au collisions at GeV
Identified mid-rapidity particle spectra of , , and
from 200 GeV p+p and d+Au collisions are reported. A
time-of-flight detector based on multi-gap resistive plate chamber technology
is used for particle identification. The particle-species dependence of the
Cronin effect is observed to be significantly smaller than that at lower
energies. The ratio of the nuclear modification factor () between
protons and charged hadrons () in the transverse momentum
range GeV/c is measured to be
(stat)(syst) in minimum-bias collisions and shows little
centrality dependence. The yield ratio of in minimum-bias d+Au
collisions is found to be a factor of 2 lower than that in Au+Au collisions,
indicating that the Cronin effect alone is not enough to account for the
relative baryon enhancement observed in heavy ion collisions at RHIC.Comment: 6 pages, 4 figures, 1 table. We extended the pion spectra from
transverse momentum 1.8 GeV/c to 3. GeV/
Longitudinal double-spin asymmetry and cross section for inclusive neutral pion production at midrapidity in polarized proton collisions at sqrt(s) = 200 GeV
We report a measurement of the longitudinal double-spin asymmetry A_LL and
the differential cross section for inclusive Pi0 production at midrapidity in
polarized proton collisions at sqrt(s) = 200 GeV. The cross section was
measured over a transverse momentum range of 1 < p_T < 17 GeV/c and found to be
in good agreement with a next-to-leading order perturbative QCD calculation.
The longitudinal double-spin asymmetry was measured in the range of 3.7 < p_T <
11 GeV/c and excludes a maximal positive gluon polarization in the proton. The
mean transverse momentum fraction of Pi0's in their parent jets was found to be
around 0.7 for electromagnetically triggered events.Comment: 6 pages, 3 figures, submitted to Phys. Rev. D (RC
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