A model for the parton distributions in hadrons

A simple model is presented for the parton distributions in hadrons. The parton momenta in the hadron rest frame are derived from a spherically symmetric, Gaussian, distribution having a width motivated by the Heisenberg uncertainty relation applied to the hadron size. Valence quarks and gluons originate from the `bare' hadron, while sea partons arise mainly from pions in hadronic fluctuations. Starting from a low Q^2 scale, the distributions are evolved with next-to-leading order DGLAP and give the proton structure function F2(x,Q^2) in good agreement with deep inelastic scattering data.Comment: 12 pages, Latex, 5 figures. Added discussion on the applicability of the model at small Q^2. Figure 3 modified to show smaller Q^

Manifestly Covariant Analysis of the QED Compton Process in ep→eγpe p\to e \gamma p and ep→eγXe p \to e \gamma X

We calculate the unpolarized QED Compton scattering cross section in a manifestly covariant way. Our approach allows a direct implementation of the specific kinematical cuts imposed in the experiments, {\it e. g.} HERA-H1. We compare the 'exact' cross section in terms of the structure functions $F_{1,2} (x_B,Q^2)$, assuming the Callan-Gross relation, with the one obtained using the equivalent photon approximation (EPA) as well as with the experimental results. We find that the agreement with the EPA is better in $x_{\gamma}$ bins, where $x_{\gamma}$ is the fraction of the longitudinal momentum of the proton carried by the virtual photon, compared to the bins in the leptonic variable $x_l$.Comment: 22 pages, 4 figures, 2 table

The Photon Structure Function at Small-x

It is shown that recent small-x measurements of the photon structure function F_2^{\gamma}(x,Q^2) by the LEP-OPAL collaboration are consistent with parameter-free QCD predictions at all presently accessible values of Q^2.Comment: 7 pages, LaTeX, 2 figure

Future physics with polarized ep-colliders

We discuss some of the physics opportunities at polarized ep-colliders. Recent studies for polarized ep-colliders include HERA, EIC and THERA.Comment: 7 pages, 6 figures, Invited talk presented at the ``International Workshop on the Spin Structure of the Proton and Polarized Collider Physics'', ECT, Trento, Italy, July 23-28, 200

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

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.

Inverse Slope Systematics in High-Energy p+p and Au+Au Reactions

We employ the Monte-Carlo PYTHIA to calculate the transverse mass spectra of various hadrons and their inverse slopes T* at m_T-m=1.5-2 GeV in p+p reactions at sqrt(s)=200 GeV. Due to (multiple) minijet production T* increases as a function of the hadron mass. Moreover, the T*(m) systematics has a ``discontinuity'' at the charm threshold, i.e. the inverse slope of D-mesons is much higher than that of non-charmed hadrons and even of the heavier Lambda_C baryon. The experimental observation of this characteristic behaviour in Au+Au collisions would indicate the absence of c-quark rescattering. In contrast, the assumption of thermalized partons and hydrodynamical evolution would lead to a smoothly increasing T*(m), without discontinuity at the charm threshold. The degree of collective transverse flow, indicated by the slope of the T*(m) systematics, depends strongly on whether kinetic equilibrium is maintained for some time after hadronization or not.Comment: 14 pages, 2 figures, REVTEX; mistake in plot of c-quark mt-distribution corrected, some references adde

Do emotions fit the frame? A critical appraisal of visual framing research approaches

With the rise of a visibly more emotional public sphere, this article asks if visual framing approaches can be enriched by the integration of emotive elements. Focussing on television news, I ask in what way emotions manifest within audio-visual material, and how these representations of emotions and emotive elements can be analysed using visual framing analysis. This understanding is grounded in two recent turns: the turn to the visual and to the affective. Both turns provide the background for current framing understandings and visual framing approaches, and for a discussion of three empirical models of analysis and their varying potential to integrate emotive elements. I distinguish here between a holistic ‘emotion frame’, emotions as narrative structures, and emotion as frame element. I argue that emotions can be best conceptualized as a frame element; and three practical realizations are discussed to what extent they are helpful to analyse emotions empirically in audio-visual news material

Deep-inelastic Electron-Photon Scattering at High Q^2 : Neutral and Charged Current Reactions

We present the results of a calculation of deep inelastic electron-photon scattering at a linear collider for very high virtuality of the intermediate gauge boson up to NLO in perturbative QCD. The real photon is produced unpolarized via the Compton back scattering of laser light of the incoming beam. For $Q^2$ values close to the masses squared of the Z and W gauge bosons, the deep inelastic electron-photon scattering process receives important contributions not only from virtual photon exchange but also from the exchange of a Z-boson and a W-boson. We find that the total cross section for center of mass energies above $500 \rm{GeV}$ is at least of ${\cal O}(pb)$ and has an important charged current contribution.Comment: Talk given at the International Conference on the Structure and Interactions of the Photon, PHOTON 99, Freiburg im Breisgau, Germany, May 23-27, 1999. To be published in the Proceedings. 6 pages, 6 postscript figures. The complete paper, including figures, is also available via anonymous ftp at ftp://ttpux2.physik.uni-karlsruhe.de/ttp99/ttp99-30/ or via www at http://www-ttp.physik.uni-karlsruhe.de/Preprints

Models for Photon-photon Total Cross-sections

We present here a brief overview of recent models describing the photon-photon cross-section into hadrons. We shall show in detail results from the eikonal minijet model, with and without soft gluon summation.Comment: 7 pages, 5 figures, laTeX, requires espcrc2.sty. To appear in the Proceedings of Photon-99, Freiburg, 23 -27 May 99, labels in the figures 1,3,4,5 corrected, one typo in an equation correcte