121214824
Pion-deuteron scattering in a D∗ model
Abstract Pion-deuteron scattering at medium energies is formulated in a model which treats the nucleon and the isolar Δ(1236) on equal footing. Following the absorption of the pion which excites (ΔN) states with different multipolarity these D∗ states of the excited deuteron are mixed and split up by the strong isobar-nucleon interaction. Those with low multipolarity dominate the differential cross section, which turns out to be in qualitative agreement with the data. As the characteristic features of the D∗ spectrum are closely related to the ΔN interaction, they should show up more or less directly in all medium energy scattering processes on the deuteron.
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.
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.
13703277
COLLECTIVE TREATMENT OF THE GIANT RESONANCES IN SPHERICAL NUCLEI.
In a collective treatment the energies of the giant resonances are given by the boundary conditions at the nuclear surface, which is subject to vibration in spherical nuclei. The general form of the coupling between these two collective motions is given by angular-momentum and parity conservation. The coupling constants are completely determined within the hydrodynamical model. In the present treatment the influence of the surface vibrations on the total photon-absorption cross section is calculated. It turns out that in most of the spherical nuclei this interaction leads to a pronounced structure in the cross section. The agreement with the experiments in medium-heavy nuclei is striking; many of the experimental characteristics are reproduced by the present calculations. In some nuclei, however, there seem to be indications of single-particle excitations which are not yet contained in this work.
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.
120745638
SHORT-RANGE CORRELATIONS AND ELASTIC ELECTRON SCATTERING.
4429028
Light echoes from ancient supernovae in the Large Magellanic Cloud
The light from historical supernovae could in principle still be visible as scattered-light echoes centuries after the explosion. The detection of light echoes could allow us to pinpoint the supernova event both in position and age and, most importantly, permit the acquisition of spectra to determine the ‘type’ of the supernova centuries after the direct light from the explosion first reached Earth. Although echoes have been discovered around some nearby extragalactic supernovae, targeted searches have not found any echoes in the regions of historical Galactic supernovae. Here we report three faint variable-surface-brightness complexes with high apparent proper motions pointing back to three of the six smallest (and probably youngest) previously catalogued supernova remnants in the Large Magellanic Cloud, which are believed to have been thermonuclear (type Ia) supernovae. Using the distance and apparent proper motions of these echo arcs, we estimate ages of 610 and 410 years for two of them.
117129613
On the Analytic Structure of Scalar Glueball Operators
The correlator of the square of the Yang-Mills field-strength tensor corresponds to a scalar glueball, i.e., to a bound-state formed by gluonic ingredients only. It has quantum numbers 0++ and its mass, as predicted by different theoretical approaches, is expected to lie between 1 and 2 GeV. Here we restrict our considerations to the Born level, that is, we consider the correlator to zeroth order in the coupling. Gluonic self-interaction is taken into account indirectly by using non-perturbative gluon propagators. The employed closed expressions are motivated by lattice and Dyson-Schwinger studies. The analytic continuation of the integrals themselves is complicated by additional obstructive structures like branch cuts and poles that are induced by the inner integral in the complex plane of the outer integration variable. We deal with this problem by deforming the outer integration contour accordingly. For different input gluon propagators we find a positive glueball spectral density which is required for physical states. Poles are, however, absent which is most likely an artifact of working at Born level.
117986736
On two- and three-point functions of Landau gauge Yang-Mills theory
We present results for the gluon and ghost propagators and the ghost-gluon vertex obtained from Dyson-Schwinger equations. In the zero temperature case we elaborate on the role of the three-gluon vertex and discuss a model that can capture its qualitative features like its anomalous dimensions and a zero crossing of the dressing function. Our results compare well with lattice data. At non-zero temperature we calculated the ghost propagator which agrees rather well with lattice results already within our simple truncation. These results are used to obtain the temperature dependence of the ghost-gluon vertex. We also explain why the ghost propagator does not react to the phase transition despite its direct coupling to the chromoelectric gluon.
6090781
Search for axions with the CDMS experiment.
We report on the first axion search results from the Cryogenic Dark Matter Search (CDMS) experiment at the Soudan Underground Laboratory. An energy threshold of 2 keV for electron-recoil events allows a search for possible solar axion conversion into photons or local galactic axion conversion into electrons in the germanium crystal detectors. The solar axion search sets an upper limit on the Primakov coupling g(agammagamma) of 2.4x10(-9) GeV-1 at the 95% confidence level for an axion mass less than 0.1 keV/c2. This limit benefits from the first precise measurement of the absolute crystal plane orientations in this type of experiment. The galactic axion search analysis sets a world-leading experimental upper limit on the axioelectric coupling g(aee) of 1.4x10(-12) at the 90% confidence level for an axion mass of 2.5 keV/c2.
40014688
Pan-STARRS1 DISCOVERY OF TWO ULTRALUMINOUS SUPERNOVAE AT z ≈ 0.9
We present the discovery of two ultraluminous supernovae (SNe) at z ≈ 0.9 with the Pan-STARRS1 Medium Deep Survey. These SNe, PS1-10ky and PS1-10awh, are among the most luminous SNe ever discovered, comparable to the unusual transients SN 2005ap and SCP 06F6. Like SN 2005ap and SCP 06F6, they show characteristic high luminosities (M_(bol) ≈ –22.5 mag), blue spectra with a few broad absorption lines, and no evidence for H or He. We have constructed a full multi-color light curve sensitive to the peak of the spectral energy distribution in the rest-frame ultraviolet, and we have obtained time series spectroscopy for these SNe. Given the similarities between the SNe, we combine their light curves to estimate a total radiated energy over the course of explosion of (0.9-1.4) × 10^(51) erg. We find photospheric velocities of 12,000-19,000 km s^(–1) with no evidence for deceleration measured across ~3 rest-frame weeks around light curve peak, consistent with the expansion of an optically thick massive shell of material. We show that, consistent with findings for other ultraluminous SNe in this class, radioactive decay is not sufficient to power PS1-10ky, and we discuss two plausible origins for these events: the initial spin-down of a newborn magnetar in a core-collapse SN, or SN shock breakout from the dense circumstellar wind surrounding a Wolf-Rayet star.