1,951 research outputs found
Parametrization of nuclear parton distributions
Optimum nuclear parton distributions are obtained by analyzing available
experimental data on electron and muon deep inelastic scattering (DIS). The
distributions are given at Q^2=1 GeV^2 with a number of parameters, which are
determined by a chi^2 analysis of the data. Valence-quark distributions are
relatively well determined at medium x, but they are slightly dependent on the
assumed parametrization form particularly at small x. Although antiquark
distributions are shadowed at small x, their behavior is not obvious at medium
x from the F_2 data. The gluon distributions could not be restricted well by
the inclusive DIS data; however, the analysis tends to support the gluon
shadowing at small x. We provide analytical expressions and computer
subroutines for calculating the nuclear parton distributions, so that other
researchers could use them for applications to other high-energy nuclear
reactions.Comment: 1+11 pages, LaTeX, amsmath.sty, wrapfig.sty, graphicx.sty, ias.cls,
ias.sty, pramana.sty, pmana10.sty, pbib.sty, times.sty, 9 eps figures.
Invited talk given at the International Symposium on Nuclear Physics, Mumbai,
India, Dec. 18-22, 2000, to be published in proceedings. Complete postscript
file is available at http://www-hs.phys.saga-u.ac.jp Email:
[email protected], [email protected],
[email protected]
Do we expect light flavor sea-quark asymmetry also for the spin-dependent distribution functions of the nucleon?
After taking account of the scale dependence by means of the standard DGLAP
evolution equation, the theoretical predictions of the chiral quark soliton
model for the unpolarized and longitudinally polarized structure functions of
the nucleon are compared with the recent high energy data. The theory is shown
to explain all the qualitative features of the experiments, including the NMC
data for , , the Hermes and NuSea
data for , the EMC and SMC data for ,
and . Among others, flavor asymmetry of the longitudinally
polarized sea-quark distributions is a remarkable prediction of this model,
i.e., it predicts that with a sizable negative coefficient
(and ) in qualitative consistency with the recent
semi-phenomenological analysis by Morii and Yamanishi.Comment: 14pages, including 5 eps_figures with epsbox.sty, late
Coexistence of Superconductivity and Charge Density Wave in SrPt2As2
SrPt2As2 is a novel arsenide superconductor, which crystallizes in the
CaBe2Ge2-type structure as a different polymorphic form of the ThCr2Si2-type
structure. SrPt2As2 exhibits a charge-density-wave (CDW) ordering at about 470
K and enters into a superconducting state at Tc = 5.2 K. The coexistence of
superconductivity and CDW refers to Peierls instability with a moderately
strong electron-phonon interaction. Thus SrPt2As2 can be viewed as a
nonmagnetic analog of iron-based superconductors, such as doped BaFe2As2, in
which superconductivity emerges in close proximity to spin-density-wave
ordering.Comment: 4 pages, 5 figure
Impact-parameter dependent nuclear parton distribution functions: EPS09s and EKS98s and their applications in nuclear hard processes
We determine the spatial (impact parameter) dependence of nuclear parton
distribution functions (nPDFs) using the -dependence of the spatially
independent (averaged) global fits EPS09 and EKS98. We work under the
assumption that the spatial dependence can be formulated as a power series of
the nuclear thickness functions . To reproduce the -dependence over the
entire range we need terms up to . As an outcome, we release two
sets, EPS09s (LO, NLO, error sets) and EKS98s, of spatially dependent nPDFs for
public use. We also discuss the implementation of these into the existing
calculations. With our results, the centrality dependence of nuclear
hard-process observables can be studied consistently with the globally fitted
nPDFs for the first time. As an application, we first calculate the LO nuclear
modification factor for primary partonic-jet production in
different centrality classes in Au+Au collisions at RHIC and Pb+Pb collisions
at LHC. Also the corresponding central-to-peripheral ratios are
studied. We also calculate the LO and NLO nuclear modification factors for
single inclusive neutral pion production, , at mid- and
forward rapidities in different centrality classes in d+Au collisions at RHIC.
In particular, we show that our results are compatible with the PHENIX
mid-rapidity data within the overall normalization uncertainties given by the
experiment. Finally, we show our predictions for the corresponding
modifications in the forthcoming p+Pb collisions at LHC.Comment: 36 page
Disorder-driven quantum phase transition from antiferromagnetic metal to insulating state in multilayered high-Tc cuprate (Cu,C)Ba2Ca4Cu5Oy
We report on superconducting(SC) characteristics for oxygen-reduced Cu-based
five-layered high-temperature superconductor (Cu,C)Ba2Ca4Cu5Oy(Cu-1245(OPT)),
which includes five-fold outer planes (OP) and four-fold inner planes (IP).As a
result of the reduction of the carrier density, the bulk SC for Cu-1245 (OPT)
takes place at the nearly optimally-doped OP with Tc= 98 K that is different
from previously-reported Cu-1245(OVD) where IP plays a primary role for the
onset of SC. It gives an evidence that the carrier density of the
optimally-doped layer determines its bulk Tc.Static antiferromagnetic(AFM)
order is evidenced at IP's by zero-field Cu-NMR at low temperature,
irrespective of the SC transition at OP's below 98K. This AFM state at IP's is
characterized by a carrier localization at low temperatures due to disorder
effect, whereas the carrier densities in each layer are similar to Hg-1245(OPT)
where the AFM metallic state are realized in IP's. This finding reinforces the
phase diagram in which the AFM metallic phase exists between AFM insulator and
SC states for the case of ideally-flat CuO2 plane without disorder.Comment: 4 pages, 5 figure
Ruthenocuprates RuSr2(Eu,Ce)2Cu2O10: Intrinsic magnetic multilayers
We report ac susceptibility data on RuSr_2(Eu,Ce)_2Cu_2O_(10-y) (Ru-1222, Ce
content x=0.5 and 1.0), RuSr_2GdCu_2O_8 (Ru-1212) and SrRuO_3. Both Ru-1222
(x=0.5, 1.0) sample types exhibit unexpected magnetic dynamics in low magnetic
fields: logarithmic time relaxation, switching behavior, and `inverted'
hysteresis loops. Neither Ru-1212 nor SrRuO_3 exhibit such magnetic dynamics.
The results are interpreted as evidence of the complex magnetic order in
Ru-1222. We propose a specific multilayer model to explain the data, and note
that superconductivity in the ruthenocuprate is compatible with both the
presence and absence of the magnetic dynamics.Comment: 9 pages, 11 figures, Revtex; submitted to Phys.Rev.
- …