422 research outputs found
Azimuthal Asymmetries in Hadronic Final States at HERA
The distribution of hadrons produced in deeply inelastic electron-proton
collisions depends on the azimuthal angle between lepton scattering plane and
hadron production plane in the photon-proton centre-of-mass frame. In addition
to the well known up-down asymmetry induced by the azimuthal dependence of the
Born level subprocess, there is also a non-vanishing left-right asymmetry,
provided the incoming electron is polarized. This asymmetry is
time-reversal-odd and induced by absorptive corrections to the Born level
process. We investigate the numerical magnitude of azimuthal asymmetries in
semi-inclusive hadron production at HERA with particular emphasis on a possible
determination of the time-reversal-odd asymmetry.Comment: 9 pages, LaTeX, 7 figures included, The complete paper, including
figures, is also available via anonymous ftp at
ftp://ttpux2.physik.uni-karlsruhe.de/ttp99/ttp99-29/ or via www at
http://www-ttp.physik.uni-karlsruhe.de/Preprints
Azimuthal Spin Asymmetries in Semi-Inclusive Production from Positron-Proton Scattering
The recent measurements of azimuthal single spin asymmetries by the HERMES
collaboration at DESY may shed some light on presently unknown fragmentation
and distribution functions. We present a study of such functions and give some
estimates of weighted integrals directly related to those measurements.Comment: 10 pages, 5 figures, comments added, figures changed, revised version
to be published on Phys. Lett.
Hadron production from quark coalescence and jet fragmentation in intermediate energy collisions at RHIC
Transverse momentum spectra of pions, protons and antiprotons in Au+Au
collisions at intermediate RHIC energy of GeV are studied in
a model that includes both quark coalescence from the dense partonic matter and
fragmentation of the quenched perturbative minijet partons. The resulting
baryon to meson ratio at intermediate transverse momenta is predicted to be
larger than that seen in experiments at higher center of mass energies.Comment: 6 pages, 2 figures. Figures replaced to differentially address the
high-pT behavior of baryon versus antibaryon to meson ratio
Inclusive B-Meson Production in e^+ e^- and p p-bar Collisions
We provide nonperturbative fragmentation functions for B mesons, both at
leading and next-to-leading order in the MS-bar factorization scheme with five
massless quark flavors. They are determined by fitting the fractional energy
distribution of B mesons inclusively produced in e^+ e^- annihilation at CERN
LEP1. Theoretical predictions for the inclusive production of B mesons with
high transverse momenta in p p-bar scattering obtained with these fragmentation
functions nicely agree, both in shape and normalization, with data recently
taken at the Fermilab Tevatron.Comment: 20 pages (Latex), 6 figures (Postscript
Compatibility of various approaches to heavy-quark fragmentation
We find that the definition of the heavy-quark fragmentation function given
by Jaffe and Randall differs by a factor of the longitudinal-momentum fraction
z from the standard Collins-Soper definition. Once this factor is taken into
account, the explicit calculation of Braaten et al. is found to be in agreement
with the general analysis of Jaffe and Randall. We also examine the model of
Peterson et al. for heavy-quark fragmentation and find that the quoted values
of the width and of the value of at the maximum are in error. The corrected
values are in agreement with the analysis of Jaffe and Randall.Comment: 4 pages late
Phenomenology of single spin asymmetries in p(transv. polarized)-p -> pion + X
A phenomenological description of single transverse spin effects in
hadron-hadron inclusive processes is proposed, assuming a generalized
factorization scheme and pQCD hard interactions. The transverse momentum, k_T,
of the quarks inside the hadrons and of the hadrons relatively to the
fragmenting quark, is taken into account in distribution and fragmentation
functions, and leads to possible non zero single spin asymmetries. The role of
k_T and spin dependent quark fragmentations -- the so-called Collins effect --
is investigated in details in p(transv. polarized)-p -> pion + X processes: it
is shown how the experimental data could be described, obtaining an explicit
expression for the spin asymmetry of a polarized fragmenting quark, on which
some comments are made. Predictions for other processes, possible further
applications and experimental tests are discussed.Comment: 20+1 pages, LaTeX, 6 eps figures, uses epsfig.sty. Version v2: Some
sentences rephrased and comments added throughout the paper; one reference
added; no changes in results and figures. Final version to be published in
Phys. Rev.
INCLUSIVE PARTICLE PRODUCTION IN \pbp COLLISIONS
We calculate the inclusive production of charged hadrons in \pbp collisions
to next-to-leading order (NLO) in the QCD improved parton model using a new set
of NLO fragmentation functions for charged pions and kaons. We predict
transverse-momentum distributions and compare them with experimental data from
the CERN S\pbpS Collider and the Fermilab Tevatron.Comment: the file containing the figures has been replaced: we correct a
mistake in the uuencoding procedure and we give the real Fig 4 instead of the
spurious one which was accidentally included in the previous file. the text
is unchanged
Heavy Flavour Production in Two-Photon Collisions
We review the production of charm and bottom quarks in two-photon collisions
at e+e- colliders. The next-to-leading order QCD predictions for total cross
sections and differential distributions are compared with recent experimental
results.Comment: 6 pages, 2 figures. Talk given at the UK Phenomenology Workshop on
Collider Physics, Durham, England, 19-24 Sep 199
Electrochemical Behavior of Nanostructured Copper Particles on Graphite for Application in Lithium Ion Batteries
Next-to-Leading Order Analysis of Inclusive and Semi-inclusive Polarized Data
We present a combined next-to-leading order QCD analysis to data on both
inclusive and semi-inclusive polarized deep inelastic scattering asymmetries.
Performing NLO QCD global fits with different sets of observables, we evaluate
the impact of the very recent semi-inclusive results presented by SMC in the
extraction of NLO polarized parton distributions.Comment: 22 pages, 4 figures include
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