Hadronic parity violation and neutron capture reactions

The hadronic weak interaction remains one of the most poorly understood sectors of the Standard Model; for obvious reasons. On the one hand, the initial and final states involve strongly bound systems of particles, for which the theoretical description (e.g. QCD) is insufficient itself and all of the current alternative or hybrid approaches are phenomenological and therefore depend on experimental input. On the other hand, experimental tests are notoriously difficult because the weak interaction observables are suppressed by the strong interaction and very high statistics measurements are needed to reach a meaningful accuracy, which in turn requires tight control of systematic uncertainties. All of this is true for both strangeness-conserving (ΔS = 0) and strangeness-changing (ΔS = 1) nonleptonic interactions. In the former category, new high intensity neutron facilities and the experiments that are proposed or are in preparation there promise sensitivities that could finally see non-zero parity violating (PV) effects in systems that have a theoretically clean interpretation. This paper provides a brief description of the physics issues and various models and introduces a few experimental efforts that are currently underway

Adiabatic loading of a Bose-Einstein condensate in a 3D optical lattice

We experimentally investigate the adiabatic loading of a Bose-Einstein condensate into an optical lattice potential. The generation of excitations during the ramp is detected by a corresponding decrease in the visibility of the interference pattern observed after free expansion of the cloud. We focus on the superfluid regime, where we show that the limiting time scale is related to the redistribution of atoms across the lattice by single-particle tunneling

All-optical formation of a Bose-Einstein condensate for applications in scanning electron microscopy

We report on the production of a F=1 spinor condensate of 87Rb atoms in a single beam optical dipole trap formed by a focused CO2 laser. The condensate is produced 13mm below the tip of a scanning electron microscope employing standard all-optical techniques. The condensate fraction contains up to 100,000 atoms and we achieve a duty cycle of less than 10s.Comment: 5 pages, 4 figure

Strong-coupling effects in the relaxation dynamics of ultracold neutral plasmas

We describe a hybrid molecular dynamics approach for the description of ultracold neutral plasmas, based on an adiabatic treatment of the electron gas and a full molecular dynamics simulation of the ions, which allows us to follow the long-time evolution of the plasma including the effect of the strongly coupled ion motion. The plasma shows a rather complex relaxation behavior, connected with temporal as well as spatial oscillations of the ion temperature. Furthermore, additional laser cooling of the ions during the plasma evolution drastically modifies the expansion dynamics, so that crystallization of the ion component can occur in this nonequilibrium system, leading to lattice-like structures or even long-range order resulting in concentric shells

Quantitative adsorbate structure determination under catalytic reaction conditions

Current methods allow quantitative local structure determination of adsorbate geometries on surfaces in ultrahigh vacuum (UHV) but are incompatible with the higher pressures required for a steady-state catalytic reactions. Here we show that photoelectron diffraction can be used to determine the structure of the methoxy and formate reaction intermediates during the steady-state oxidation of methanol over Cu(110) by taking advantage of recent instrumental developments to allow near-ambient pressure x-ray photoelectron spectroscopy. The local methoxy site differs from that under static UHV conditions, attributed to the increased surface mobility and dynamic nature of the surface under reaction conditions

The \Delta contribution to the parity-violating nucleon-nucleon force

Because the nucleon may be excited and transformed into a virtual $\Delta$ resonance easily, we consider the decuplet contribution to the parity-violating (PV) nucleon-nucleon interaction in the chiral effective field theory. The effective PV nucleon-nucleon potential is derived without introducing any unknown coupling constants.Comment: 5 pages, 2 figures. The version appeared in Chinese Physics C (HEP & NP

Precision measurement of spin-dependent interaction strengths for spin-1 and spin-2 87Rb atoms

We report on precision measurements of spin-dependent interaction-strengths in the 87Rb spin-1 and spin-2 hyperfine ground states. Our method is based on the recent observation of coherence in the collisionally driven spin-dynamics of ultracold atom pairs trapped in optical lattices. Analysis of the Rabi-type oscillations between two spin states of an atom pair allows a direct determination of the coupling parameters in the interaction hamiltonian. We deduce differences in scattering lengths from our data that can directly be compared to theoretical predictions in order to test interatomic potentials. Our measurements agree with the predictions within 20%. The knowledge of these coupling parameters allows one to determine the nature of the magnetic ground state. Our data imply a ferromagnetic ground state for 87Rb in the f=1 manifold, in agreement with earlier experiments performed without the optical lattice. For 87Rb in the f=2 manifold the data points towards an antiferromagnetic ground state, however our error bars do not exclude a possible cyclic phase.Comment: 11 pages, 5 figure

Strong Metal Support Interaction as a Key Factor of Au Activation in CO Oxidation

We address the question of the nature of Au NP activation and through a combination of experimental and theoretical techniques. In situ XPS measurements of Au TiO2 during CO oxidation show high catalytic activity can be associated with the formation of an ionic Au species. DFT calculations performed on Au TiO2 show that the formation of such ionic Au is due to a strong metal support interaction between Au and reduced and defective TiO2. TEM supports these findings, indicating the formation of an overlayer of transition metal oxide support on Au NPs after CO oxidation. These results suggest TiO2 lattice oxygen is involved directly in CO oxidation, which was confirmed with labeled 18O2 experiment

Methanol oxidation over model cobalt catalysts: Influence of the cobalt oxidation state on the reactivity

X-ray photoelectron and absorption spectroscopies (XPS and XAS) combined with on-line mass spectrometry were applied under working catalytic conditions to investigate the methanol oxidation on cobalt. Two cobalt oxidation states (Co3O4 and CoO) were prepared and investigated as regards their influence on the catalytic activity and selectivity. In addition adsorbed species were monitored in the transition of the catalyst from the non-active to the active state. It was unequivocally shown that the surface oxidation state of cobalt is readily adapted to the oxygen chemical potential in the CH3OH/O2 reaction mixture. In particular, even in rich to oxygen mixtures the Co3O4 surface is partially reduced, while the degree of surface reduction is higher as the methanol concentration in the mixture increases. The reaction selectivity depends on the cobalt oxidation state with the more reduced samples favouring the partial oxidation of methanol to formaldehyde. In the absence of oxygen, methanol is effectively reducing cobalt to the metallic state, promoting also hydrogen and CO production. Direct evidence of methoxy and formate species adsorbed on the surface upon reaction was found by analysing the O 1s and C 1s photoelectron spectra. However, the surface coverage of those species was not proportional to the catalytic activity, indicating that in the absence of surface oxygen, these species might act also as reaction inhibitors