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We calculate the electromagnetic form factors of the Λ 0 and ∑ 0 hyperons using a relativised constituent quark model which includes correction terms related to the potential acting between the quarks and to the center-of-mass motion during the photon-baryon scattering. Effects of the broken SU(3) symmetry on the charge distribution inside the baryon are analysed by comparing the results to the nucleonic case. Magnetic transition moments and decay widths are calculated for the most important hyperon resonances.

In this paper we investigate the electromagnetic form factors of baryons and their resonances using the framework of a relativized constituent quark model. Beyond the usual single-quark transition ansatz, we incorporate relativistic corrections which are welldetermined by the intrinsic interaction and confinement forces between the quarks. Furthermore we separate off for the compound three-quark system the relativistic center-of-mass motion by an approximately Lorentz-invariant approach. In this way for the first time recoil effects could be explicity studied. Using the harmonic oscillator wavefunctions with the configuration mixing as derived in the Isgur-Karl model, after restoring gauge invariance our relativized interaction hamiltonian can be used to calculate the transversely and longitudinally polarized photon transition form factors of the baryons.

In this paper, we present numerical results for electroproduction amplitudes of proton resonances and electromagnetic nucleon form factors calculated in a relativized quark model. Interactions with both transversely and longitudinally polarized virtual photons were considered. Contributions of the different effects included in our approach have been analysed through a sample comparison with the available data. We also discuss the validity of the usual single-quark transition ansatz and possible parametrizations of the potential acting between the constituent quarks of the baryon. Impressive agreement is obtained with the nucleon form factor data up to squared momentum transfers of 2.5 GeV2, but still some problems remain with the Δ(1232) and higher resonances.

Im Oktober des letzten Jahres konnte die Kultusministerin des nordlichsten der neuen Bundeslander feststellen, das die 1. Stufe der personellen Erneuerung der Hochschulen abgeschlossen sei. Mecklenburg-Vorpommern war damit das erste der neuen Bundeslander, das diese Zwischenstufe des Umbaus des Hochschulsystems erreichte. Fur die Physik lautet das Ergebnis, das etwa drei Viertel der C2-, C3- und C4-Professuren an den beiden Universitaten des Landes in Greifswald und Rostock sowie an der neugegrundeten Fachhochschule Wismar durch Ubernahme von qualifizierten Fachkollegen besetzt werden konnten. Die restlichen Positionen werden nach dem ublichen Berufungsverfahren ausgeschrieben.

We study the current-algebra approach to the Gerasimov-Drell-Hearn sum rule, paying particular attention to the infinite-momentum limit. Employing the order-alpha^2 Weinberg-Salam model of weak interactions as a testing ground, we find that the legitimacy of the infinite-momentum limit is intimately connected with the validity of the naive equal-times algebra of electric charge densities. Our results considerably reduce the reliability of a recently proposed modification of the Gerasimov-Drell-Hearn sum rule, originating from an anomalous charge-density algebra., 12 pages; 6 figures; LaTeX; submitted to Z.Phys.C

In the history of Elementary Particle Physics quite a few experimental results aroused the interest of a broader Physics community. This time experiments with polarized electron and muon beams on polarized proton targets gave rise to excitements leading to headlines like [1] “The Proton Spin Crisis — Where, oh where is the proton spin?” There are good reasons for such an excitement since basically one experimental number — see equation (1) below ! — has put a big question mark to our understanding of the structure of the most abundant and important hadron: the proton. Therefore this year at each Particle or Nuclear Physics Conference reviews on the “Proton Spin Problem” are given and especially at this Symposium on High Energy Spin Physics it is a most appropriate topic.

We investigate the helicity asymmetries and isospin ratios of radiative transition amplitudes for nucleon resonances electroproduced off proton and neutron targets at momentum transfers of ${Q}^{2}\ensuremath{\le}3$ Ge${\mathrm{V}}^{2}$. Calculations were done in the framework of a relativized constituent quark model which includes many-body effects due to the quark interaction potential and a consistent relativistic approximation of the center-of-mass motion of the three-quark system. We find significant deviations from the predictions of the nonrelativistic quark models and the ${\mathrm{SU}(6)}_{W}$ algebraic approach based on the single-quark-transition hypothesis. Our calculated relativistic corrections lead to an overall better agreement with the experimental data. The question of whether some of the low-lying $P$-wave baryons are of hybrid nature is briefly discussed. Finally we analyze the electroexcitation of the missing (20,${1}^{+}$) $P$-wave resonances.

Mit den Worten, die Berliner Physikalische Gesellschaft war „ein Kreis aufstrebender Talente, der durch die entschlossene Selbsthilfe eines freiwilligen Zusammenschlusses, eine Statte schuf, an der sich durch lebhafte, anregende Wechselbeziehung eine seltene Blute geistigen Lebens entfaltete”, kennzeichnete der Mathematiker Felix Klein die Physikalische Gesellschaft zu Berlin [1]. In der Tat gilt dieser Bezug auf die Physiker selbst -nach § 3 der DPG-Satzung - auch heute noch. Er spiegelt sich auch in den Themen der Empfehlungen und Stellungnahmen wider, die die DPG abgegeben hat. Dennoch hat die Aufgabe, fur die Physik und die Physiker zu wirken, die DPG immer wieder veranlast, Empfehlungen auch nach ausen an die politischgesellschaftliche Umwelt zu richten.

Stellungnahmen der Konferenz der Fachbereiche Physik (KFP) und der Gesellschaft fur Didaktik der Chemie und Physik (GDCP) zu den „Einheitlichen Prufungsanforderungen in der Abiturprufung/Chemie/Physik”.

Based on the nowadays available phenomenological multipoles for pion photoproduction, a systematic dispersion theoretic calculation of Compton partial amplitudes has been performed. By comparing with the new experimental data in the Δ(1232) region it is found that the hitherto existing discrepancies between the data and theory remain. Our results allow us to isolate the basis of this problem. It is due to the fact that the imaginary parts of the Compton amplitudes determined already by unitarity, give too large contributions to the cross section thus leaving no space for real parts required by the dispersion integrals. Therefore a simultaneous partial-wave analysis for Compton scattering and pion photoproduction was carried through employing only the unitarity connections between both. The resulting amplitudes give a good fit to the Compton cross section and all photoproduction data; moreover the photoproduction multipoles agree essentially with those of the previous analyses. On the other hand for Compton scattering, phenomenological amplitudes are obtained for the first time and a model independent test of dispersion theoretic amplitudes can be carried out. For the resonating fMM1+ amplitude which describes the M1 excitation and deexcitation to the Δ-isobar, large discrepancies have been found. Possible consequences especially for the forward scattering amplitude and the validity of the Kramers-Kronig relation are discussed.

Das in jedem zweiten Jahr stattfindende grose internationale Treffen der Elementarteilchenphysiker, auch unter dem Namen „Rochester-Konferenz” bekannt (vgl. Phys. Bl. 42(1986) Nr. 11, S. 388–389), fuhrte in diesem Jahr ca. 1000 Physiker aus allen Landern der Erde nach Munchen. Das lokale Organisationskomitee unter Leitung der Professoren G. Buschhorn und K. Pretzl vom MPI fur Physik und Astrophysik, Werner-Heisenberg-Institut, hatte die Tagung optimal vorbereitet, so das sich die Teilnehmer ohne Reibungsverluste dem wissenschaftlichen Programm widmen konnten. Fur die deutschen Physiker war die XXIV. Rochester-Konferenz ein Ereignis von besonderer Bedeutung, denn zum ersten Mal fand dieses herausragende Treffen der Hochenergiephysiker auf bundesdeutschem Boden statt. Im folgenden geben ein Theoretiker (Prof. H. Rollnik, Bonn) und ein Experimentalphysiker (Prof. D. Wegener, Dortmund) ihre Eindrucke von der Konferenz wieder.

The predictions of reggeized vector meson exchange in γp→pπo are discussed. For t small, the calculated ω- exchange agrees with available data. The theoretical minimum at t = -0.6 (GeV/c)2 is tentatively removed at 2 GeV by a resonant background.

The Weizsacker-Williams method is discussed using modern techniques. It is shown how gauge invariance guarantees the vanishing of the longitudinal cross-section for zero momentum-transfer. Explicit calculations are carried out for virtual Compton scattering and applied to determine the radiative corrections due to hard photons in muon-electron scattering.

Die bisherige allgemeine Theorie von Regelsystemen wird dadurch verallgemeinert, das fur die Regelstarke eine zeitliche Variation zugelassen wird, die das System in einem endlichen Zeitintervall in den gewunschten End-zustand uberfuhrt. Die Losung dieses Problems gelingt mit Hilfe einer allgemeinen Laplace-Transformation. Unter der Voraussetzung, das die auftretenden Differential-Operatoren Polynome beliebigen, aber endlichen Grades sind, werden die strengen Losungen in Integralform aufgeschrieben und asymptotische Entwicklungen sowie Potenzreihen daraus gefolgert. Auserdem werden die Bedingungen fur die Stabilitat des Regelsystems angegeben. Eine Anwendung der Formeln soll in einer spateren Arbeit erfolgen. The existing general theory of servomechanism is generalized so as to cover systems where the control strength varies with time in such a way that the system is brougth into the prescribed final state within a finite period of time. The problem is solved by using a general Laplace transformation. For the case that the differential operators are polynoms of any finite degree rigorous solutions in integral form are given from which asymptotic expansion and power series are derived. The stability conditions of the system are also derived. Applications will be dealt with in a forthcoming paper.

Das von den Verfassern in der fruheren Arbeit [1] gestellte Regelproblem mit zeitlich variabler Regelstarke wird vollstandig gelost. Dazu wird. 1. der Einflus einer auseren Kraft durch Berechnung des entsprechenden partikularen Integrals bestimmt und. 2. der Fehler ermittelt, der bei beliebig vorgegebenen Anfangsbedingungen des Systems, zur Zeit t = 0 besteht, wo das System den gewunschten Endzustand erreicht haben soll. The problem of servomechanism with variable control strength which has been posed in a previous paper [1] is now solved completely by. 1. determining the influence of an external force by means of the corresponding particular integral, and 2. determining the deviation from the prescribed end position at t = 0 for arbitrary initial conditions.

Theπ+−π0 mass difference is calculated from spectral function sum rules with finite widths ofρ and A1 The deviation from the zero width approximation is found to be small.

Renormalization of gauge theories.- Unified models of electromagnetic and weak interactions.- Osterwalder-Schrader positivity in conformal invariant quantum field theory.- Quantum gravity.- Quantum field theory and statistical mechanics.- Critical phenomena and the renormalization group.- Renormalization group solution of Ising spin models.- Covariant parton model.- Quark confinement in gauge theories of strong interactions.- Parton models for weak and electromagnetic interactions.- The relativistic string.- Fermi - bose - supersymmetry.- Strings, conductive and otherwise.- Hadron physics at ISR energies.- Review of results obtained at the cern intersecting storage rings.

In these lectures I shall describe the progress of our understanding of the photon hadron interaction in the resonance region. I will address myself to the fundamental properties of the electromagnetic hadron current and its behaviour under symmetries as well as to a detailed description of photon couplings of hadronic states. The progress to date is based on an impressive accumulation of experimental information about photon hadron processes and its phenomenological interpretation and has led to a remarkable improvement of our insight in the electromagnetic structures of hadrons.