720 research outputs found
Do we understand the incompressibility of neutron-rich matter?
The ``breathing mode'' of neutron-rich nuclei is our window into the
incompressibility of neutron-rich matter. After much confusion on the
interpretation of the experimental data, consistency was finally reached
between different models that predicted both the distribution of isoscalar
monopole strength in finite nuclei and the compression modulus of infinite
matter. However, a very recent experiment on the Tin isotopes at the Research
Center for Nuclear Physics(RCNP) in Japan has again muddled the waters.
Self-consistent models that were successful in reproducing the energy of the
giant monopole resonance (GMR) in nuclei with various nucleon asymmetries (such
as 90Zr, 144Sm, and 208Pb) overestimate the GMR energies in the Tin isotopes.
As important, the discrepancy between theory and experiment appears to grow
with neutron excess. This is particularly problematic as models artificially
tuned to reproduce the rapid softening of the GMR in the Tin isotopes become
inconsistent with the behavior of dilute neutron matter. Thus, we regard the
question of ``why is Tin so soft?'' as an important open problem in nuclear
structure.Comment: 12 pages, 3 figures, and 1 table. Submitted to the "Focus issue on
Open Problems in Nuclear Structure", Journal of Physics
Update of High Resolution (e,e'K^+) Hypernuclear Spectroscopy at Jefferson Lab's Hall A
Updated results of the experiment E94-107 hypernuclear spectroscopy in Hall A
of the Thomas Jefferson National Accelerator Facility (Jefferson Lab), are
presented. The experiment provides high resolution spectra of excitation energy
for 12B_\Lambda, 16N_\Lambda, and 9Li_\Lambda hypernuclei obtained by
electroproduction of strangeness. A new theoretical calculation for
12B_\Lambda, final results for 16N_\Lambda, and discussion of the preliminary
results of 9Li_\Lambda are reported.Comment: 8 pages, 5 figures, submitted to the proceedings of Hyp-X Conferenc
Weak charge form factor and radius of 208Pb through parity violation in electron scattering
We use distorted wave electron scattering calculations to extract the weak
charge form factor F_W(q), the weak charge radius R_W, and the point neutron
radius R_n, of 208Pb from the PREX parity violating asymmetry measurement. The
form factor is the Fourier transform of the weak charge density at the average
momentum transfer q=0.475 fm. We find F_W(q) =0.204 \pm 0.028 (exp) \pm
0.001 (model). We use the Helm model to infer the weak radius from F_W(q). We
find R_W= 5.826 \pm 0.181 (exp) \pm 0.027 (model) fm. Here the exp error
includes PREX statistical and systematic errors, while the model error
describes the uncertainty in R_W from uncertainties in the surface thickness
\sigma of the weak charge density. The weak radius is larger than the charge
radius, implying a "weak charge skin" where the surface region is relatively
enriched in weak charges compared to (electromagnetic) charges. We extract the
point neutron radius R_n=5.751 \pm 0.175 (exp) \pm 0.026 (model) \pm 0.005
(strange) fm$, from R_W. Here there is only a very small error (strange) from
possible strange quark contributions. We find R_n to be slightly smaller than
R_W because of the nucleon's size. Finally, we find a neutron skin thickness of
R_n-R_p=0.302\pm 0.175 (exp) \pm 0.026 (model) \pm 0.005 (strange) fm, where
R_p is the point proton radius.Comment: 5 pages, 1 figure, published in Phys Rev. C. Only one change in this
version: we have added one author, also to metadat
A comprehensive framework tool for performance assessment of NBS for hydro-meteorological risk management
publishedVersio
Are standard cell culture conditions adequate for human umbilical cord blood mesenchymal stem cells?
Performance of the Two Aerogel Cherenkov Detectors of the JLab Hall A Hadron Spectrometer
We report on the design and commissioning of two silica aerogel Cherenkov
detectors with different refractive indices. In particular, extraordinary
performance in terms of the number of detected photoelectrons was achieved
through an appropriate choice of PMT type and reflector, along with some design
considerations. After four years of operation, the number of detected
photoelectrons was found to be noticeably reduced in both detectors as a result
of contamination, yellowing, of the aerogel material. Along with the details of
the set-up, we illustrate the characteristics of the detectors during different
time periods and the probable causes of the contamination. In particular we
show that the replacement of the contaminated aerogel and parts of the
reflecting material has almost restored the initial performance of the
detectors.Comment: 18 pages, 9 Figures, 4 Tables, 44 Reference
Quark-Hadron Duality in Neutron (3He) Spin Structure
We present experimental results of the first high-precision test of
quark-hadron duality in the spin-structure function g_1 of the neutron and
He using a polarized 3He target in the four-momentum-transfer-squared range
from 0.7 to 4.0 (GeV/c)^2. Global duality is observed for the spin-structure
function g_1 down to at least Q^2 = 1.8 (GeV/c)^2 in both targets. We have also
formed the photon-nucleon asymmetry A_1 in the resonance region for 3He and
found no strong Q^2-dependence above 2.2 (GeV/c)^2.Comment: 13 pages, 3 figure
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