4,192,410 research outputs found
Nuclear corrections in neutrino-nucleus DIS and their compatibility with global NPDF analyses
We perform a global chi^2-analysis of nuclear parton distribution functions
using data from charged current neutrino-nucleus deep-inelastic scattering
(DIS), charged-lepton-nucleus DIS, and the Drell-Yan (DY) process. We show that
the nuclear corrections in nu-A DIS are not compatible with the predictions
derived from l^+A DIS and DY data. We quantify this result using a
hypothesis-testing criterion based on the chi^2 distribution which we apply to
the total chi^2 as well as to the chi^2 of the individual data sets. We find
that it is not possible to accommodate the data from nu-A and l^+A DIS by an
acceptable combined fit. Our result has strong implications for the extraction
of both nuclear and proton parton distribution functions using combined
neutrino and charged-lepton data sets.Comment: 5 page
PDFs for nuclear targets
Understanding nuclear effects in parton distribution functions (PDF) is an
essential component needed to determine the strange and anti-strange quark
contributions in the proton. In addition Nuclear Parton Distribution Functions
(NPDF) are critically important for any collider experiment with nuclei (e.g.
RHIC, ALICE). Here two next-to-leading order chi^2-analyses of NPDF are
presented. The first uses neutral current charged-lepton Deeply Inelastic
Scattering (DIS) and Drell-Yan data for several nuclear targets and the second
uses neutrino-nucleon DIS data. We compare the nuclear corrections factors
(F_2^Fe/F_2^D) for the charged-lepton data with other results from the
literature. In particular, we compare and contrast fits based upon the
charged-lepton DIS data with those using neutrino-nucleon DIS data.Comment: 5 pages, to appear in Proceedings of DIS 201
Gravitational coupling to two-particle bound states and momentum conservation in deep inelastic scattering
The momentum conservation sum rule for deep inelastic scattering (DIS) from
composite particles is investigated using the general theory of relativity. For
two 1+1 dimensional examples, it shown that covariant theories automatically
satisy the DIS momentum conservation sum rule provided the bound state is
covariantilly normalized. Therefore, in these cases the two DIS sum rules for
baryon conservation and momentum conservation are equivalent
Star Formation in Dwarf Galaxies of the Nearby Centaurus A Group
We present Halpha narrow-band imaging of 17 dwarf irregular galaxies (dIs) in
the nearby Centaurus A Group. Although all large galaxies of the group have a
current or recent enhanced star formation episode, the dIs have normal star
formation rates and do not contain a larger fraction of dwarf starbursts than
other nearby groups. Relative distances between dIs and larger galaxies of the
group can be computed in 3D since most of them have now fairly accurately known
distances. We find that the dI star formation rates do not depend on local
environment, and in particular they do not show any correlation with the
distance of the dI to the nearest large galaxy of the group. There is a clear
morphology-density relation in the Centaurus A Group, similarly to the Sculptor
and Local Groups, in the sense that dEs/dSphs tend to be at small distances
from the more massive galaxies of the group, while dIs are on average at larger
distances. We find four transition dwarfs in the Group, dwarfs that show
characteristics of both dE/dSphs and dIs, and which contain cold gas but no
current star formation. Interestingly the transition dwarfs have an average
distance to the more massive galaxies which is intermediate between those of
the dEs/dSphs and dIs, and which is quite large: 0.54 +- 0.31 Mpc. This large
distance poses some difficulty for the most popular scenarios proposed for
transforming a dI into a dE/dSph (ram-pressure with tidal stripping or galaxy
harassment). If the observed transition dwarfs are indeed missing links between
dIs and dE/dSphs, their relative isolation makes it less likely to have been
produced by these mechanisms. We propose that an inhomogeneous IGM containing
higher density clumps would be able to ram-pressure stripped the dIs at such
large distances.Comment: 57 pages, 10 fi5gure
Strange sea asymmetry from global QCD fits
We present a preliminary account of a new global QCD analysis of DIS data,
including recent DIS measurements. The model-independent cross
section reanalysis by CCFR allows a new determination of the strange sea
asymmetry, whose first moment is found to be small. The impact on the NuTeV
measurement of is discussed.Comment: Presentation at the DIS 2003 conferenc
Structure Functions are not Parton Probabilities
Parton distributions given by deep inelastic lepton scattering (DIS) are not
equal to the probabilities of finding those partons in the parent wave
function. Soft rescattering of the struck parton within the coherence length of
the hard process influences the DIS cross section and gives dynamical phases to
the scattering amplitudes. This gives rise to diffractive DIS, shadowing in
nuclear targets and transverse spin asymmetry.Comment: Talk at ICHEP 2002, Amsterdam (July 2002). 3 pages, 1 figur
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