407 research outputs found
Interference Fragmentation Functions and the Nucleon's Transversity
We introduce twist-two quark interference fragmentation functions in helicity
density matrix formalism and study their physical implications. We show how the
nucleon's transversity distribution can be probed through the final state
interaction between two mesons (, , or ) produced
in the current fragmentation region in deep inelastic scattering on a
transversely polarized nucleon.Comment: Final version to be published in Phys. Rev. Let
Final-state Interaction Effects on Inclusive Two-particle Production in Electron-positron Annihilation
The final-state interaction effects on the inclusive two-particle production
in electron-positron annihilation are investigated within the context of the
one-photon annihilation approximation. Such effects are characterized by one
structure function in the decomposition of the hadronic tensor. On the basis of
the positivity, we derived an inequality to bound this structure function. The
price to access it experimentally is to polarize longitudinally one of the
initial-state beam, to say, the electron beam, and measure the corresponding
single spin asymmetry. By combining the Callan-Gross relation with our
positivity analysis, we obtain an upper bound for the single spin asymmetry
considered.Comment: Revtex, 11 pages, 1 figure in postscript, to appear in J. Phys.
Resonant Diffraction Radiation from an Ultrarelativistic Particle Moving Close to a Tilted Grating
A simple model for calculating the diffraction radiation characteristics from
an ultrarelativistic charged particle moving close to a tilted ideally
conducting strip is developed. Resonant diffraction radiation (RDR) is treated
as a superposition of the radiation fields for periodically spaced strips. The
RDR characteristics have been calculated as a function of the number of grating
elements, tilted angle, and initial particle energy. An analogy with both the
resonant transition radiation in absorbing medium and the parametric X-ray
radiation is noted.Comment: 17 pages, 12 figures, RevTe
Transversity K Factors for Drell-Yan
The question of the K factor in transversely polarised Drell-Yan (DY)
processes is examined. The transverse-spin case is peculiar for the absence of
a reference point in deeply inelastic scattering (DIS). Therefore, in order to
study more fully the possible effects of higher-order corrections on DY
asymmetries, a DIS definition for transversity is devised using a hypothetical
scalar (Higgs-like) vertex. The results show that some care may be required in
interpreting experimentally extracted partonic transversity, in particular when
comparing with model calculations or predictions.Comment: 8 pages, 4 figures (eps and feynmp); uses standard LaTeX/MiKTeX
packages [svjour.cls, amsmath, bbm, feynmp, graphicx, maybemath, natbib,
psfrag, slashed] some homespun packages (included in the zip file);
discussion augmented, 1 figure removed; resubmitted to Eur. Phys. J. section
Transverse Double-Spin Asymmetries for Muon Pair Production in pp-Collisions
We calculate the rapidity dependence of the transverse double-spin asymmetry
for the Drell-Yan process to next-to-leading order in the strong coupling.
Input transversity distributions are obtained by saturating the Soffer
inequality at a low hadronic mass scale. Results for the polarized BNL-RHIC
proton-proton collider and the proposed HERA-N fixed-target experiment are
presented, and the influence of the limited muon acceptance of the detectors on
measurements of the asymmetry is studied in detail.Comment: 7 pages including 5 figures; significantly shortened, to be published
in Phys. Rev.
CMS ridge effect at LHC as a manifestation of bremstralung of gluons due to the quark-anti-quark string formation
The recently reported effect of long-range near-side angular correlations at
LHC occurs for large multiplicities of particles with
. To understand the effect several possibilities have
been discussed. In the letter we propose a simple qualitative mechanism which
corresponds to gluon bremstralung of quarks moving with acceleration
appropriate to the quark--anti-quark string. The smallness of azimuthal angle
difference along with large at large multiplicities
in this interval of are natural in the mechanism. The mechanism predicts
also bremstralung photons with mean values of and
.Comment: 5 pages, 3 figure
Chiral-Odd and Spin-Dependent Quark Fragmentation Functions and their Applications
We define a number of quark fragmentation functions for spin-0, -1/2 and -1
hadrons, and classify them according to their twist, spin and chirality. As an
example of their applications, we use them to analyze semi-inclusive
deep-inelastic scattering on a transversely polarized nucleon.Comment: 19 pages in Plain TeX, MIT CTP #221
Novel Quark Fragmentation Functions and the Nucleon's Transversity Distribution
We define twist-two and twist-three quark fragmentation functions in Quantum
Chromodynamics (QCD) and study their physical implications. Using this
formalism we show how the nucleon's transversity distribution can be measured
in single pion inclusive electroproduction.Comment: 10 pages, uses PHYZZX macro package, 2 PostScript figures (added
using FIGURES). MIT-CTP-215
Positivity Constraints for Spin-Dependent Parton Distributions
We derive new positivity constraints on the spin-dependent structure
functions of the nucleon. These model independent results reduce conside\-rably
their domain of allowed values, in particular for the chiral-odd parton
distribution .Comment: 8 pages,CPT-94/P.3059,LaTex,3 fig available on cpt.univ-mrs.fr
directory pub/preprints/94/fundamental-interactions/94-P.305
A positron source using an axially oriented crystal associated to a granular amorphous converter
Submitted to Chinese Physics CA non conventional positron source using the intense Îł radiation from an axially oriented monocrystal which materialize into e+e- pairs in a granular amorphous converter is described. The enhancement of photon radiation by multi-GeV electrons crossing a tungsten crystal along its axis is reported. The resulting enhancement of pair production in an amorphous converter placed 2 meters downstream, is also reported. Sweeping off the charged particles from the crystal by a bending magnet upstream of the converter allows a significant reduction of the deposited energy density. Substituting a granular target made of small spheres to the usual compact one, makes easier the energy dissipation. The deposited energy and corresponding heating are analyzed and solutions for cooling are proposed. The configurations studied here for this kind of positron source allow its consideration for unpolarized positrons for the ILC
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