1,102 research outputs found
Leading logarithm calculation of the e^+ e^- -> e^+ \nu_e \bar{u} d cross section
We analytically evaluate in the leading logarithm approximation the
differential cross section for e^+ e^- -> e^+ \nu_e \bar{u} d. We compare our
order \alpha^4 \alpha_s^0 leading-log result to the order \alpha^4 \alpha_s^0
exact result obtained from the GRC4F Monte Carlo program. Finally we use the
Gluck, Reya, Schienbien distribution of partons in a virtual photon, which
incorporates both evolution and nonperturbative strong interaction
contributions, to obtain better estimates of the differential cross section.Comment: 10 pages including 9 figure
Longitudinally Polarized Photoproduction of Inclusive Hadrons Beyond the Leading Order
We present a complete next-to-leading order QCD calculation for
single-inclusive large-pT hadron production in longitudinally polarized
lepton-nucleon collisions, consistently including ``direct'' and ``resolved''
photon contributions. This process could be studied experimentally at a future
polarized lepton-proton collider like eRHIC at BNL. We examine the sensitivity
of such measurements to the so far completely unknown parton content of
circularly polarized photons.Comment: 15 pages, 7 eps figure
Threshold Resummation for W-Boson Production at RHIC
We study the resummation of large logarithmic perturbative corrections to the
partonic cross sections relevant for the process pp -> W^+- X at the BNL
Relativistic Heavy Ion Collider (RHIC). At RHIC, polarized protons are
available, and spin asymmetries for this process will be used for precise
measurements of the up and down quark and anti-quark distributions in the
proton. The corrections arise near the threshold for the partonic reaction and
are associated with soft-gluon emission. We perform the resummation to
next-to-leading logarithmic accuracy, for the rapidity-differential cross
section. We find that resummation leads to relatively moderate effects on the
cross sections and spin asymmetries.Comment: 25 pages, 15 figures as eps files. One reference added and typo
correcte
Probing the parton densities of virtual photons with the reaction gamma^*gamma->jets at LEP
We present a next-to-leading order calculation of jet production in
gamma^*gamma collisions from e+e- scattering in a region where the virtuality
Q^2 of the probing virtual photon is small compared to the transverse jet
energy. The calculation is based on the phase-space slicing method. The initial
state singularity of the virtual photon is factorized into the structure
function of the virtual photon, using the MS-bar factorization scheme for
virtual photons. Numerical results are presented for LEP2 conditions. The
perturbative stability of the pure direct virtual photon approach is compared
to that of including resolved virtual photons in different regions of Q^2. We
make predictions for cross sections which suggest that different
parametrizations of virtual photon parton densities should be distinguishable
by measurements of jet cross sections at LEP.Comment: 19 pages, 8 eps figue
Longitudinally Polarized Photoproduction of Inclusive Hadrons at Fixed-Target Experiments
We present a detailed phenomenological study of spin-dependent
single-inclusive high-p_T hadron photoproduction with particular emphasis on
the kinematics relevant for the Compass and Hermes fixed-target experiments. We
carefully examine the theoretical uncertainties associated with the only
moderate transverse momenta accessible in such measurements and analyze the
sensitivity of the relevant spin asymmetries to the gluon polarization in the
nucleon as well as to the completely unknown parton content of circularly
polarized photons.Comment: 12 pages, 14 figures; final version to appear in EPJC; comparison to
E155 data and references adde
Has the QCD RG-Improved Parton Content of Virtual Photons been Observed?
It is demonstrated that present and DIS ep data on the structure of
the virtual photon can be understood entirely in terms of the standard `naive'
quark--parton model box approach. Thus the QCD renormalization group (RG)
improved parton distributions of virtual photons, in particular their gluonic
component, have not yet been observed. The appropriate kinematical regions for
their future observation are pointed out as well as suitable measurements which
may demonstrate their relevance.Comment: 24 pages, LaTeX, 5 figure
Heavy Quark Initiated Contributions to Deep Inelastic Structure Functions
We present O(alpha_s^1) corrections to deep inelastic scattering amplitudes
on massive quarks obtained within the scheme of Aivazis, Collins, Olness and
Tung (ACOT). After identifying the correct subtraction term the convergence of
these contributions towards the analogous coefficient functions for massless
quarks, obtained within the modified minimal subtraction scheme (MSbar), is
demonstrated. Furthermore, the quantitative relevance of the contributions to
neutral current (NC) and charged current (CC) structure functions is
investigated for several choices of the factorization scale.Comment: 29 pages, 6 figures; uses epsfig.sty, amssymb.sty, axodraw.sty; minor
changes for publication in Phys. Rev.
Generalized parton distributions of the nucleon in constituent quark models
Generalized parton distributions (GPDs) are studied at the hadronic
(nonperturbative) scale within different assumptions based on a relativistic
constituent quark model. In particular, by means of a meson-cloud model we
investigate the role of nonperturbative antiquark degrees of freedom and the
valence quark contribution. A QCD evolution of the obtained GPDs is used to add
perturbative effects and to investigate the GPDs' sensitivity to the
nonperturbative ingredients of the calculation at larger (experimental) scale.Comment: 4 pages, 1 figure, presented at the Baryon-04 Conference, Palaiseau
(France), October 25-29, 2004. Nuclear Physics A, to be publishe
New proton polarized structure functions in charged current processes at HERA
Estimates for longitudinal spin asymmetries which single out new polarized
nucleon structure functions in deeply inelastic charged current interactions at
HERA energies are given, exploiting their interpretation in terms of polarized
quark distributions. These asymmetries turn out to be large and allow a
measurement of the new polarized structure functions and ,
which would add valuable tests and information on the spin content of quarks
inside a polarized proton. We also show that single spin asymmetries in neutral
current interactions are very small.Comment: LaTeX, 8 pages, 6 figure
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