674 research outputs found
Leading Chiral Contributions to the Spin Structure of the Proton
The leading chiral contributions to the quark and gluon components of the
proton spin are calculated using heavy-baryon chiral perturbation theory.
Similar calculations are done for the moments of the generalized parton
distributions relevant to the quark and gluon angular momentum densities. These
results provide useful insight about the role of pions in the spin structure of
the nucleon, and can serve as a guidance for extrapolating lattice QCD
calculations at large quark masses to the chiral limit.Comment: 8 pages, 2 figures; a typo in Ref. 7 correcte
The Direct Measurement of Circulation in Free Surface Vortices
Ultrasonic techniques have been used to directly and non-intrusively measure the circulation of free surface vortices. All experiments were performed in a vertical cylindrical tank with a central drain and a tangential inlet The circulation was measured on a closed triangular path by measuring the difference in upstream and downstream transit-times. Circulation was measured as a function of the Reynolds and Froude numbers and was found to increase as the Reynolds and Froude numbers increased. The circulation was also found to be proportional to the square of the ratio of the drain diameter to cylinder diameter while the ratio of fluid depth to cylinder diameter was held constant. Minimum surface elevations were measured at various conditions and attempts were made to correlate them with measured circulation
A GLOBAL QCD STUDY OF DIRECT PHOTON PRODUCTION
A global QCD analysis of the direct photon production process from both fixed
target and collider experiments is presented. These data sets now completely
cover the parton range from 0.01 to 0.6, thereby providing a stringent test
of perturbative QCD and parton distributions. Previous detailed studies of
direct photons emphasized fixed target data. We find most data sets have a
steeper distribution than the QCD prediction. Neither global fits with
new parton distributions nor improved photon fragmentation functions can
resolve this problem since the deviation occurs at different values for
experiments at different energies. A more likely explanation is the need for
additional broadening of the of the initial state partons. The magnitude
and the possible physical origin of this effect are investigated and discussed.Comment: 8 page Latex file using epsf.sty for figures. 6 eps figures submitted
separately in uuencoded file
Tevatron Mass Limits for Heavy Quarks Decaying via Flavor Changing Neutral Current
The dimuon and dielectron data from the Tevatron collider are used
to probe for heavy quarks, which decay dominantly via flavour changing neutral
current. Depending on whether the decay occurs at the tree or loop
level, one gets a lower mass limit of 85 or 75 GeV. The former applies to
singlet, vector doublet and mirror type quarks while the latter applies to a
lefthanded quark doublet of the fourth generation.Comment: 13 pages, TIFR/TH/92-58, Two figures to be supplied on reques
Soft Color Enhancement of the Production of J/psi's by Neutrinos
We calculate the production of J/psi mesons by neutrino-nucleon collisions in
fixed target experiments. Soft color, often referred to as color evaporation
effects, enhance production cross sections due to the contribution of color
octet states. Though still small, J/\psi production may be observable in
present and future experiments like NuTeV and muon colliders.Comment: 7 pages, Revtex, 4 postscript figures, uses epsfig.st
Dynamics of Light Antiquarks in the Proton
We present a comprehensive analysis of the recent data from the E866
experiment at Fermilab on Drell-Yan production in pD and pp collisions, which
indicates a non-trivial x-dependence for the asymmetry between u-bar and d-bar
quark distributions in the proton. The relatively fast decrease of the
asymmetry at large x suggests the important role played by the chiral structure
of the nucleon, in particular the pi-N and pi-Delta components of the nucleon
wave function. At small x the data require an additional non-chiral component,
which may be attributed to the Pauli exclusion principle as first suggested by
Field and Feynman.Comment: version to appear in Phys. Rev.
Shadowing in neutrino deep inelastic scattering and the determination of the strange quark distribution
We discuss shadowing corrections to the structure function in neutrino
deep-inelastic scattering on heavy nuclear targets. In particular, we examine
the role played by shadowing in the comparison of the structure functions
measured in neutrino and muon deep inelastic scattering. The importance of
shadowing corrections in the determination of the strange quark distributions
is explained.Comment: 22 pages, 7 figure
The Leading Particle Effect from Heavy-Quark Recombination
The leading particle effect in charm hadroproduction is an enhancement of the
cross section for a charmed hadron D in the forward direction of the beam when
the beam hadron has a valence parton in common with the D. The large D+/D-
asymmetry observed by the E791 experiment is an example of this phenomenon. We
show that the heavy-quark recombination mechanism provides an economical
explanation for this effect. In particular, the D+/D- asymmetry can be fit
reasonably well using a single parameter whose value is consistent with a
recent determination from charm photoproduction.Comment: Revtex file, 4 pages, 3 figure
Lambda Polarization in Polarized Proton-Proton Collisions at RHIC
We discuss Lambda polarization in semi-inclusive proton-proton collisions,
with one of the protons longitudinally polarized. The hyperfine interaction
responsible for the - and - mass splittings gives
rise to flavor asymmetric fragmentation functions and to sizable polarized
non-strange fragmentation functions. We predict large positive Lambda
polarization in polarized proton-proton collisions at large rapidities of the
produced Lambda, while other models, based on SU(3) flavor symmetric
fragmentation functions, predict zero or negative Lambda polarization. The
effect of and decays is also discussed. Forthcoming
experiments at RHIC will be able to differentiate between these predictions.Comment: 18 pages, 5 figure
Bloom-Gilman duality of inelastic structure functions in nucleon and nuclei
The Bloom-Gilman local duality of the inelastic structure function of the
proton, the deuteron and light complex nuclei is investigated using available
experimental data in the squared four-momentum transfer range from 0.3 to 5
(GeV/c)**2. The results of our analysis suggest that the onset of the
Bloom-Gilman local duality is anticipated in complex nuclei with respect to the
case of the protonand the deuteron. A possible interpretation of this result in
terms of a rescaling effect is discussed with particular emphasis to the
possibility of reproducing the damping of the nucleon-resonance transitions
observed in recent electroproduction data off nuclei.Comment: revised version, to appear in Physical Review
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