961 research outputs found
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
Ultracold Atoms as a Target: Absolute Scattering Cross-Section Measurements
We report on a new experimental platform for the measurement of absolute
scattering cross-sections. The target atoms are trapped in an optical dipole
trap and are exposed to an incident particle beam. The exponential decay of the
atom number directly yields the absolute total scattering cross-section. The
technique can be applied to any atomic or molecular species that can be
prepared in an optical dipole trap and provides a large variety of possible
scattering scenarios
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
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
A Scanning Electron Microscope for Ultracold Atoms
We propose a new technique for the detection of single atoms in ultracold
quantum gases. The technique is based on scanning electron microscopy and
employs the electron impact ionization of trapped atoms with a focussed
electron probe. Subsequent detection of the resulting ions allows for the
reconstruction of the atoms position. This technique is expected to achieve a
much better spatial resolution compared to any optical detection method. In
combination with the sensitivity to single atoms, it makes new in situ
measurements of atomic correlations possible. The detection principle is also
well suited for the addressing of individual sites in optical lattices.Comment: 5 pages, 2 figure
Fast nonadiabatic dynamics of many-body quantum systems
Modeling many-body quantum systems with strong interactions is one of the core challenges of modern physics. A range of methods has been developed to approach this task, each with its own idiosyncrasies, approximations, and realm of applicability. However, there remain many problems that are intractable for existing methods. In particular, many approaches face a huge computational barrier when modeling large numbers of coupled electrons and ions at finite temperature. Here, we address this shortfall with a new approach to modeling many-body quantum systems. On the basis of the Bohmian trajectory formalism, our new method treats the full particle dynamics with a considerable increase in computational speed. As a result, we are able to perform large-scale simulations of coupled electron-ion systems without using the adiabatic Born-Oppenheimer approximation
Ion structure in warm dense matter: benchmarking solutions of hypernetted-chain equations by first-principle simulations
We investigate the microscopic structure of strongly coupled ions in warm dense matter using ab initio simulations and hypernetted chain (HNC) equations. We demonstrate that an approximate treatment of quantum effects by weak pseudopotentials fails to describe the highly degenerate electrons in warm dense matter correctly. However, one-component HNC calculations for the ions agree well with first-principles simulations if a linearly screened Coulomb potential is used. These HNC results can be further improved by adding a short-range repulsion that accounts for bound electrons. Examples are given for recently studied light elements, lithium and beryllium, and for aluminum where the extra short-range repulsion is essential
Probing the hydrogen melting line at high pressures by dynamic compression
We investigate the capabilities of dynamic compression by intense heavy ion beams to yield information about the high pressure phases of hydrogen. Employing ab initio simulations and experimental data, a new wide range equation of state for hydrogen is constructed. The results show that the melting line up to its maximum as well as the transition from molecular fluids to fully ionized plasmas can be tested with the beam parameters soon to be available. We demonstrate that x-ray scattering can distinguish between phases and dissociation states
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
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