798 research outputs found
Probing Quark Fragmentation Functions for Spin-1/2 Baryon Production in Unpolarized Annihilation
We study the measurement of the quark fragmentation functions for spin-1/2
baryon production ( and , in particular) in unpolarized
annihilation. The spin-dependent fragmentation functions
and can be probed in the process as a result of quark-antiquark
spin correlation and the weak decay of the baryons. The relevant cross section
is expressed as a product of the two-jet cross-section, the fragmentation
functions, and the differential width of the hyperon decay.Comment: 17 pages, ReVTeX with (1 figure available from authors), MIT-CTP:
#236
Comparison of quantum mechanical and classical trajectory calculations of cross sections for ion-atom impact ionization of negative - and positive -ions for heavy ion fusion applications
Stripping cross sections in nitrogen have been calculated using the classical
trajectory approximation and the Born approximation of quantum mechanics for
the outer shell electrons of 3.2GeV I and Cs ions. A large
difference in cross section, up to a factor of six, calculated in quantum
mechanics and classical mechanics, has been obtained. Because at such high
velocities the Born approximation is well validated, the classical trajectory
approach fails to correctly predict the stripping cross sections at high
energies for electron orbitals with low ionization potential.Comment: submitted to Phys. Rev.
Enhanced Fusion-Evaporation Cross Sections in Neutron-Rich Sn on Ni
Evaporation residue cross sections have been measured with neutron-rich
radioactive Sn beams on Ni in the vicinity of the Coulomb
barrier. The average beam intensity was particles per second
and the smallest cross section measured was less than 5 mb. Large subbarrier
fusion enhancement was observed. Coupled-channels calculations taking into
account inelastic excitation and neutron transfer underpredict the measured
cross sections below the barrier.Comment: 4 pages including 1 table and 3 figure
Strange chiral nucleon form factors
We investigate the strange electric and magnetic form factors of the nucleon
in the framework of heavy baryon chiral perturbation theory to third order in
the chiral expansion. All counterterms can be fixed from data. In particular,
the two unknown singlet couplings can be deduced from the parity-violating
electron scattering experiments performed by the SAMPLE and the HAPPEX
collaborations. Within the given uncertainties, our analysis leads to a small
and positive electric strangeness radius, .
We also deduce the consequences for the upcoming MAMI A4 experiment.Comment: 7 pp, REVTeX, uses epsf, minor correction
Gravitational-wave Detection With Matter-wave Interferometers Based On Standing Light Waves
We study the possibility of detecting gravitational-waves with matter-wave
interferometers, where atom beams are split, deflected and recombined totally
by standing light waves. Our calculation shows that the phase shift is
dominated by terms proportional to the time derivative of the gravitational
wave amplitude. Taking into account future improvements on current
technologies, it is promising to build a matter-wave interferometer detector
with desired sensitivity.Comment: 7 pages, 3 figures. To be published in General Relativity and
Gravitatio
Progress in the determination of the cross section
Improving previous calculations, we compute the cross section using QCD sum rules. Our sum rules for the , , and hadronic
matrix elements are constructed by using vaccum-pion correlation functions, and
we work up to twist-4 in the soft-pion limit. Our results suggest that, using
meson exchange models is perfectly acceptable, provided that they include form
factors and that they respect chiral symmetry. After doing a thermal average we
get mb at T=150\MeV.Comment: 22 pages, RevTeX4 including 7 figures in ps file
Parity violating target asymmetry in electron - proton scattering
We analyze the parity-violating (PV) components of the analyzing power in
elastic electron-proton scattering and discuss their sensitivity to the strange
quark contributions to the proton weak form factors. We point out that the
component of the analyzing power along the momentum transfer is independent of
the electric weak form factor and thus compares favorably with the PV beam
asymmetry for a determination of the strangeness magnetic moment. We also show
that the transverse component could be used for constraining the strangeness
radius. Finally, we argue that a measurement of both components could give
experimental information on the strangeness axial charge.Comment: 24 pages, Latex, 5 eps figures, submitted to Phys.Rev.
Nuclear shadowing in deep inelastic scattering on nuclei: leading twist versus eikonal approaches
We use several diverse parameterizations of diffractive parton distributions,
extracted in leading twist QCD analyses of the HERA diffractive deep inelastic
scattering (DIS) data, to make predictions for leading twist nuclear shadowing
of nuclear quark and gluon distributions in DIS on nuclei. We find that the
HERA diffractive data are sufficiently precise to allow us to predict large
nuclear shadowing for gluons and quarks, unambiguously. We performed detailed
studies of nuclear shadowing for up and charm sea quarks and gluons within
several scenarios of shadowing and diffractive slopes, as well as at central
impact parameters. We compare these leading twist results with those obtained
from the eikonal approach to nuclear shadowing (which is based on a very
different space-time picture) and observe sharply contrasting predictions for
the size and Q^2-dependence of nuclear shadowing. The most striking differences
arise for the interaction of small dipoles with nuclei, in particular for the
longitudinal structure function F_{L}^{A}.Comment: 43 pages, 16 figures, requires JHEP style fil
Strange form factors in the context of SAMPLE, HAPPEX, and A4 experiments
The strange properties of the nucleon are investigated within the framework
of the SU(3) chiral quark-soliton model assuming isospin symmetry and applying
the symmetry conserving SU(3) quantization. We present the form factors
, and the electric and magnetic strange form
factors incorporating pion and kaon asymptotics. The results
show a fairly good agreement with the recent experimental data from the SAMPLE
and HAPPEX collaborations. We also present predictions for future measurements
including the A4 experiment at MAMI (Mainz).Comment: 10 pages with four figures. RevTeX4 is used. Few lines are changed.
Accepted for publication in Phys.Rev.
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