Influence of molecular temperature on the coherence of fullerenes in a near-field interferometer

We study C70 fullerene matter waves in a Talbot-Lau interferometer as a function of their temperature. While the ideal fringe visibility is observed at moderate molecular temperatures, we find a gradual degradation of the interference contrast if the molecules are heated before entering the interferometer. A method is developed to assess the distribution of the micro-canonical temperatures of the molecules in free flight. This way the heating-dependent reduction of interference contrast can be compared with the predictions of quantum theory. We find that the observed loss of coherence agrees quantitatively with the expected decoherence rate due to the thermal radiation emitted by the hot molecules.Comment: 11 pages, 9 figure

Electroexcitation of the Roper resonance from CLAS data

The helicity amplitudes of the electroexcitation of the Roper resonance on proton are extracted at 1.7 < Q2 < 4.2 GeV2 from recent high precision JLab-CLAS cross sections data and longitudinally polarized beam asymmetry for pi+ electroproduction on protons. The analysis is made using two approaches, dispersion relations and unitary isobar model, which give consistent results. It is found that the transverse helicity amplitude for the gamma* p --> P11(1440) transition, which is large and negative at Q2=0, becomes large and positive at Q2 ~ 2 GeV2, and then drops slowly with Q2. Longitudinal helicity amplitude, that was previously found from CLAS data as large and positive at Q2=0.4,0.65 GeV2, drops with Q2. These results rule out the presentation of P11(1440) as a 3qG hybrid state, and provide strong evidence in favor of this resonance as a first radial excitation of the 3q ground state.Comment: 3 pages, 2 figures, Talk on the Workshop on "The Physics of Excited Nucleons", Bonn, Germany, October 200

Updated resonance photo-decay amplitudes to 2 GeV

We present the results of an energy-dependent and set of single-energy partial-wave analyses of single-pion photoproduction data. These analyses extend from threshold to 2 GeV in the laboratory photon energy, and update our previous analyses to 1.8 GeV. Photo-decay amplitudes are extracted for the baryon resonances within this energy range. We consider two photoproduction sum rules and the contributions of two additional resonance candidates found in our most recent analysis of $\pi N$ elastic scattering data. Comparisons are made with previous analyses.Comment: Revtex, 26 pages, 3 figures. Postscript figures available from ftp://clsaid.phys.vt.edu/pub/pr or indirectly from http://clsaid.phys.vt.edu/~CAPS

Hadronic Electromagnetic Properties at Finite Lattice Spacing

Electromagnetic properties of the octet mesons as well as the octet and decuplet baryons are augmented in quenched and partially quenched chiral perturbation theory to include O(a) corrections due to lattice discretization. We present the results for the SU(3) flavor group in the isospin limit as well as the results for SU(2) flavor with non-degenerate quarks. These corrections will be useful for extrapolation of lattice calculations using Wilson valence and sea quarks, as well as calculations using Wilson sea quarks and Ginsparg-Wilson valence quarks.Comment: 19 pages, 0 figures, RevTeX

Diffraction of complex molecules by structures made of light

We demonstrate that structures made of light can be used to coherently control the motion of complex molecules. In particular, we show diffraction of the fullerenes C60 and C70 at a thin grating based on a standing light wave. We prove experimentally that the principles of this effect, well known from atom optics, can be successfully extended to massive and large molecules which are internally in a thermodynamic mixed state and which do not exhibit narrow optical resonances. Our results will be important for the observation of quantum interference with even larger and more complex objects.Comment: 4 pages, 3 figure

Sum rule for the backward spin polarizability of the nucleon from a backward dispersion relation

A new sum rule for $\gamma_\pi$, the backward spin polarizability of the nucleon, is derived from a backward-angle dispersion relation. Taking into account single- and multi-pion photoproduction in the s-channel up to the energy 1.5 GeV and resonances in the t-channel with mass below 1.5 GeV, it is found for the proton and neutron that $[\gamma_\pi]_p$ = -39.5 +/- 2.4 and $[\gamma_\pi]_n$ = 52.5 +/- 2.4, respectively, in units of 10^{-4} fm^4.Comment: 10 pages, 1 figure, revtex. Submitted to Phys. Lett.

Li/MgO with spin sensors as catalyst for the oxidative coupling of methane

Co-doping of Li/MgO, a well-known catalyst for the oxidative coupling of methane, was investigated. It is demonstrated that Gd3+ and Fe3+ can be used as spin sensors in these solids to investigate the structure via EPR spectroscopy. These aliovalent ions occupy Mg2+ sites in the lattice; the expected coupling with charge-compensating neighboring Li+ was detected. A strong increase of the activity was observed. However, all samples suffered from deactivation. The solubility of Gd3+ in MgO turned out to be inhibited. No such restriction was observed for Fe3+

Collisional decoherence observed in matter wave interferometry

We study the loss of spatial coherence in the extended wave function of fullerenes due to collisions with background gases. From the gradual suppression of quantum interference with increasing gas pressure we are able to support quantitatively both the predictions of decoherence theory and our picture of the interaction process. We thus explore the practical limits of matter wave interferometry at finite gas pressures and estimate the required experimental vacuum conditions for interferometry with even larger objects.Comment: 4 pages, 3 figure

Dressing the nucleon in a dispersion approach

We present a model for dressing the nucleon propagator and vertices. In the model the use of a K-matrix approach (unitarity) and dispersion relations (analyticity) are combined. The principal application of the model lies in pion-nucleon scattering where we discuss effects of the dressing on the phase shifts.Comment: 17 pages, using REVTeX, 6 figure