121335171
A study of meson-baryon couplings in the constituent quark model
Within the framework of the constituent quark model we discuss the effects of different types of meson-baryon-baryon vertex operators on the form factors and the coupling strengths of the lowest-lying positive and negative parity non-strange baryons. We compare the quark pair creation model (3P0-model) with the SU(6)-model in which mesons are treated as elementary fields that directly couple to the quarks. The latter model is employed both in the so-called static limit and in a modification motivated by Galilei invariance. It is demonstrated that the inclusion of non-static effects simulates some features of the3P0 vertex. Especially the reaction πN→ππN is found to be very sensitive to the different assumptions on the dynamics of theq¯q pair creation process. More indirect hints for the internal structure of the mesons might be obtained from the predicted asymmetry for the two form factors ofN→Δ+π andΔ→N+π, which occurs in the3P0-model, only.
121918725
Meson-nucleus interaction - on the use of intensive meson beams for subnuclear research -
Abstract The use of intensive pion and kaon beams for subnuclear research is discussed. The goals of such investigations are briefly sketched and illustrated for some typical examples of specific flavour transfer reactions. It turns out that the meson beams which will be available at the proposed EHF will open up a new aera of subnuclear research. Such investigation touch upon quite fundamental questions of hadronic physics.
120855950
Pionic and electromagnetic excitation of A* resonances
The nuclear excitation spectrum in the Delta (3,3) energy range is studied by comparing elastic pion scattering with coherent neutral pion photoproduction. The corresponding multipole excitation strength distributions are found to be quite different. This emphasises the role of the electromagnetic excitations of nuclei for the investigation of the A* resonances which is complementary to their mesonic excitation. Results are presented for 12C( gamma , pi 0) 12C(GS); they are compared with those of the phenomenological isobar doorway model and of DWIA calculations.
117998395
Quark excitations of nuclei - A new frontier in nuclear research -
The investigation of nuclei in the energy domain of the elementary N*-resonances (i.e. for 200 MeV < Eexc < 2 GeV) opens up a new and important domain of nuclear research for essentially two reasons: (i) the quark structure of the nuclear constituent, the nucleon, leads to new nuclear phenomena; their investigation appears to be of fundamental importance for the understanding of complex hadronic systems; (ii) the nucleus can be used as a unique laboratory to test QCD in the nonasymptotic region where perturbative approaches fail. This is of particular interest, e.g. for the confinement problem. — Some specific aspects of subnuclear research are discussed in connection with the analysis of recent experiments and, in particular, in view of a possible strategy for a systematic investigation of nuclear quark excitations.
120745638
SHORT-RANGE CORRELATIONS AND ELASTIC ELECTRON SCATTERING.
118736183
Unified Description of Pion-Photo-Production and Elastic Pion Scattering on the Deuteron in the Isobar-Doorway Model
It has been recognized recently1 that the strong dominance of the Δ(1236) isobar in nuclear reactions at medium energies advocates an explicit treatment of this degree of freedom in nuclei (in contrast to its implicit incorporation in an optical model description). Such a model, phrased commonly as isobar doorway or A* model1 has two particularly interesting features, (i) it forms a natural basis for a unified description of different isobar dominated scattering processes; (ii) it offers a more or less direct test of the isobar self energy in nuclei or, equivalently, of the ΔN interaction. An ideal testing ground for such a model seems to be deuteron: with all many-body complications being absent, predictions for scattering reactions on the deuteron should reflect and in this way allow direct investigation of the various ingredients of the model.
18086811
Scattered-Light Echoes from the Historical Galactic Supernovae Cassiopeia A and Tycho (SN 1572)
We report the discovery of an extensive system of scattered light echo arclets associated with the recent supernovae in the local neighbourhood of the Milky Way: Tycho (SN 1572) and Cassiopeia A. Existing work suggests that the Tycho SN was a thermonuclear explosion while the Cas A supernova was a core collapse explosion. Precise classifications according to modern nomenclature require spectra of the outburst light. In the case of ancient SNe, this can only be done with spectroscopy of their light echo, where the discovery of the light echoes from the outburst light is the first step. Adjacent light echo positions suggest that Cas A and Tycho may share common scattering dust structures. If so, it is possible to measure precise distances between historical Galactic supernovae. On-going surveys that alert on the development of bright scattered-light echo features have the potential to reveal detailed spectroscopic information for many recent Galactic supernovae, both directly visible and obscured by dust in the Galactic plane. Subject headings: ISM: individual(Cas A) — ISM: individual(Tycho) — supernova:general — supernova remnants
7904061
Confinement and Green functions in Landau-gauge QCD
Institut fur Physik, Karl-Franzens-Universitat, Universitatsplatz 5, A-8010 Graz, AustriaIn a functionalapproachto QCD the infraredbehaviourof LandaugaugeGreenfunctionsis inves-tigated. Positivity violation for, and thus conﬁnement of, gluons is demonstrated, and the analyticstructure of the gluon propagator is studied. Quark conﬁnem ent is related to an infrared diver-gence of the quark-gluon vertex. In the latter various components are dynamically induced dueto the spontaneous breaking of chiral symmetry. As a result an infrared ﬁnite running coupling inthe Yang-Mills sector is derived whereas the running coupling related to the quark-gluonvertex isinfrared divergent. Based on a truncation for the quark-gluon vertex Dyson-Schwinger equation,which respects the analytically determined infrared behavior, numerical results for the coupledsystem of the quark propagator and vertex Dyson-Schwinger equations are presented. The result-ing quark mass function as well as the vertex function show only a very weak dependence on thecurrent quark mass in the deep infrared. From this we infer by an analysis of the quark-quarkscattering kernel a linearly rising quark potential with an almost mass independent string tensionin the case of broken chiral symmetry.8th Conference Quark Conﬁnement and the Hadron SpectrumSeptember 1-6, 2008Mainz, Germany
52245958
Revealing Bell’s nonlocality for unstable systems in high energy physics
Entanglement and its consequences—in particular the violation of Bell inequalities, which defies our concepts of realism and locality—have been proven to play key roles in Nature by many experiments for various quantum systems. Entanglement can also be found in systems not consisting of ordinary matter and light, i.e. in massive meson–antimeson systems. Bell inequalities have been discussed for these systems, but up to date no direct experimental test to conclusively exclude local realism was found. This mainly stems from the fact that one only has access to a restricted class of observables and that these systems are also decaying. In this Letter we put forward a Bell inequality for unstable systems which can be tested at accelerator facilities with current technology. Herewith, the long awaited proof that such systems at different energy scales can reveal the sophisticated “dynamical” nonlocal feature of Nature in a direct experiment gets feasible. Moreover, the role of entanglement and $\mathcal{CP}$ violation, an asymmetry between matter and antimatter, is explored, a special feature offered only by these meson–antimeson systems.
6288625
Combined limits on WIMPs from the CDMS and EDELWEISS experiments
The CDMS and EDELWEISS collaborations have combined the results of their direct searches for dark matter using cryogenic germanium detectors. The total data set represents 614  kg·days equivalent exposure. A straightforward method of combination was chosen for its simplicity before data were exchanged between experiments. The results are interpreted in terms of limits on spin-independent weakly interacting, massive particle (WIMP)-nucleon cross section. For a WIMP mass of 90  GeV/c^2, where this analysis is most sensitive, a cross section of 3.3×10^(-44)  cm^2 is excluded at 90% C.L. At higher WIMP masses, the combination improves the individual limits, by a factor 1.6 above 700  GeV/c^2. Alternative methods of combining the data provide stronger constraints for some ranges of WIMP masses and weaker constraints for others.
119277250
Infrared singularities in Landau gauge Yang-Mills theory
We present a more detailed picture of the infrared regime of Landau-gauge Yang-Mills theory. This is done within a novel framework that allows one to take into account the influence of finite scales within an infrared power counting analysis. We find that there are two qualitatively different infrared fixed points of the full system of Dyson-Schwinger equations. The first extends the known scaling solution, where the ghost dynamics is dominant and gluon propagation is strongly suppressed. It features in addition to the strong divergences of gluonic vertex functions in the previously considered uniform scaling limit, when all external momenta tend to zero, also weaker kinematic divergences, when only some of the external momenta vanish. The second solution represents the recently proposed decoupling scenario where the gluons become massive and the ghosts remain bare. In this case we find that none of the vertex functions is enhanced, so that the infrared dynamics is entirely suppressed. Our analysis also provides a strict argument why the Landau-gauge gluon dressing function cannot be infrared divergent.