31,771 research outputs found
Next-to-Leading Order Hard Scattering Using Fully Unintegrated Parton Distribution Functions
We calculate the next-to-leading order fully unintegrated hard scattering
coefficient for unpolarized gluon-induced deep inelastic scattering using the
logical framework of parton correlation functions developed in previous work.
In our approach, exact four-momentum conservation is maintained throughout the
calculation. Hence, all non-perturbative functions, like parton distribution
functions, depend on all components of parton four-momentum. In contrast to the
usual collinear factorization approach where the hard scattering coefficient
involves generalized functions (such as Dirac -functions), the fully
unintegrated hard scattering coefficient is an ordinary function. Gluon-induced
deep inelastic scattering provides a simple illustration of the application of
the fully unintegrated factorization formalism with a non-trivial hard
scattering coefficient, applied to a phenomenologically interesting case.
Furthermore, the gluon-induced process allows for a parameterization of the
fully unintegrated gluon distribution function.Comment: 22 pages, Typos Fixed, Reference Added, Minor Clarification Adde
Fully Unintegrated Parton Correlation Functions and Factorization in Lowest Order Hard Scattering
Motivated by the need to correct the potentially large kinematic errors in
approximations used in the standard formulation of perturbative QCD, we
reformulate deeply inelastic lepton-proton scattering in terms of gauge
invariant, universal parton correlation functions which depend on all
components of parton four-momentum. Currently, different hard QCD processes are
described by very different perturbative formalisms, each relying on its own
set of kinematical approximations. In this paper we show how to set up
formalism that avoids approximations on final-state momenta, and thus has a
very general domain of applicability. The use of exact kinematics introduces a
number of significant conceptual shifts already at leading order, and tightly
constrains the formalism. We show how to define parton correlation functions
that generalize the concepts of parton density, fragmentation function, and
soft factor. After setting up a general subtraction formalism, we obtain a
factorization theorem. To avoid complications with Ward identities the full
derivation is restricted to abelian gauge theories; even so the resulting
structure is highly suggestive of a similar treatment for non-abelian gauge
theories.Comment: 44 pages, 69 figures typos fixed, clarifications and second appendix
adde
Angular momentum exchange between coherent light and matter fields
Full, three dimensional, time-dependent simulations are presented
demonstrating the quantized transfer of angular momentum to a Bose-Einstein
condensate from a laser carrying orbital angular momentum in a
Laguerre-Gaussian mode. The process is described in terms of coherent Bragg
scattering of atoms from a chiral optical lattice. The transfer efficiency and
the angular momentum content of the output coupled vortex state are analyzed
and compared with a recent experiment.Comment: 4 pages, 4 figure
On scale dependence of QCD string operators
We have obtained a general solution of evolution equations for QCD twist-2
string operators in form of expansion over complete set of orthogonal
eigenfunctions of evolution kernels in coordinate-space representation. In the
leading logarithmic approximation the eigenfunctions can be determined using
constraints imposed by conformal symmetry. Explicit formulae for the LO
scale-dependence of quark and gluon twist-2 string operators are given
Kinematics of Current Region Fragmentation in Semi-Inclusive Deeply Inelastic Scattering
Different kinematical regimes of semi-inclusive deeply inelastic scattering
(SIDIS) processes correspond to different underlying partonic pictures, and it
is important to understand the transition between them. This is particularly
the case when there is sensitivity to intrinsic transverse momentum, in which
case kinematical details can become especially important. We address the
question of how to identify the current fragmentation region --- the
kinematical regime where a factorization picture with fragmentation functions
is appropriate. We distinguish this from soft and target fragmentation regimes.
Our criteria are based on the kinematic regions used in derivations of
factorization theorems. We argue that, when hard scales are of order a few
GeVs, there is likely significant overlap between different rapidity regions
that are normally understood to be distinct. We thus comment on the need to
take this into account with more unified descriptions of SIDIS, which should
span all rapidities for the produced hadron. Finally, we propose general
criteria for estimating the proximity to the current region at large Q.Comment: 9 Pages, 5 figures; minor clarifications and corrections, version
appearing in Physics Letters
Dihadron fragmentation functions and high Pt hadron-hadron correlations
We propose the formulation of a dihadron fragmentation function in terms of
parton matrix elements. Under the collinear factorization approximation and
facilitated by the cut-vertex technique, the two hadron inclusive cross section
at leading order (LO) in e+ e- annihilation is shown to factorize into a short
distance parton cross section and the long distance dihadron fragmentation
function. We also derive the DGLAP evolution equation of this function at
leading log. The evolution equation for the non-singlet quark fragmentation
function is solved numerically with a simple ansatz for the initial condition
and results are presented for cases of physical interest.Comment: Latex, 4 pages, 4 figures, talk given at Quark Matter 2004, To appear
in J. Phys.
Airborne laser topographic mapping results from initial joint NASA/US Army Corps of Engineers experiment
Initial results from a series of joint NASA/US Army Corps of Engineers experiments are presented. The NASA Airborne Oceanographic Lidar (AOL) was exercised over various terrain conditions, collecting both profile and scan data from which river basin cross sections are extracted. Comparisons of the laser data with both photogrammetry and ground surveys are made, with 12 to 27 cm agreement observed over open ground. Foliage penetration tests, utilizing the unique time-waveform sampling capability of the AOL, indicate 50 cm agreement with photogrammetry (known to have difficulty in foliage covered terrain)
Mediating the cultivation of fear through media literacy education
College students (N = 110) received a media literacy intervention based on critical thinking or they received no intervention. Students were also classified as low or high television viewers based on responses to a Television Use Survey. Fear was measured with a Safety Survey and analyzed with a 2 Intervention x 2 Television Viewing ANOVA. Fear was expected to be lower in the intervention and low television viewing groups than in the no intervention and high television viewing groups. However, no results were significant
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