It has been proposed that there could be a mirror copy of the standard model particles, restoring the parity symmetry in the weak interaction on the global level. Oscillations between a neutral ...standard model particle, such as the neutron, and its mirror counterpart could potentially answer various standing issues in physics today. Astrophysical studies and terrestrial experiments led by ultracold neutron storage measurements have investigated neutron to mirror-neutron oscillations and imposed constraints on the theoretical parameters. Recently, further analysis of these ultracold neutron storage experiments has yielded statistically significant anomalous signals that may be interpreted as neutron to mirror-neutron oscillations, assuming nonzero mirror magnetic fields. The neutron electric dipole moment collaboration performed a dedicated search at the Paul Scherrer Institute and found no evidence of neutron to mirror-neutron oscillations. Thereby, the following new lower limits on the oscillation time were obtained: τnn′>352 s at B′=0 (95% C.L.), τnn′>6s for 0.4μT<B′<25.7μT (95% C.L.), and τnn′/cosβ>9s for 5.0μT<B′<25.4μT (95% C.L.), where β is the fixed angle between the applied magnetic field and the local mirror magnetic field, which is assumed to be bound to the Earth. These new constraints are the best measured so far around B′∼10μT and B′∼20μT.
We have developed a position response calibration method for a micro-channel plate (MCP) detector with a delay-line anode position readout scheme. Using an in situ calibration mask, an accuracy of ...8µm and a resolution of 85µm (FWHM) have been achieved for MeV-scale α particles and ions with energies of ∼10keV. At this level of accuracy, the difference between the MCP position responses to high-energy α particles and low-energy ions is significant. The improved performance of the MCP detector can find applications in many fields of AMO and nuclear physics. In our case, it helps reducing systematic uncertainties in a high-precision nuclear β-decay experiment.
We provide the experimental evidence that the single electron capture process in slow collisions between O^{3+} ions and neon dimer targets leads to an unexpected production of low-energy electrons. ...This production results from the interatomic Coulombic decay process, subsequent to inner-shell single electron capture from one site of the neon dimer. Although pure one-electron capture from the inner shell is expected to be negligible in the low collision energy regime investigated here, the electron production due to this process overtakes by 1 order of magnitude the emission of Auger electrons by the scattered projectiles after double-electron capture. This feature is specific to low charge states of the projectile: similar studies with Xe^{20+} and Ar^{9+} projectiles show no evidence of inner-shell single-electron capture. The dependence of the process on the projectile charge state is interpreted using simple calculations based on the classical over the barrier model.
We measured kinetic energies of the fragment ions of argon dimers multiply ionized by low-energy Ar(9+) collisions. For (Ar2)(4+) dissociation, the asymmetric channel (Ar(3+) + Ar(+)) yield is found ...unexpectedly higher than the symmetric channel (Ar(2+) + Ar(2+)) yield in contrast with previous observation for covalent molecules or clusters. For the dissociation channel (Ar2)(2+)→Ar(+) + Ar(+), two well-separated peaks were observed, clearly evidencing that the direct Coulombic dissociation and the radiative charge transfer followed by ionic dissociation alternatively occur for the dicationic dimers. The respective intensity of these two peaks provides a direct mean to unravel the respective proportion of one-site and two-site double-electron capture, which are found equal for this collision system.
Electron capture processes for low energy Ar(9+) ions colliding with Ar(2) dimer targets are investigated, focusing attention on charge sharing between the two Ar atoms as a function of the molecular ...orientation and the impact parameter. A preference for charge-asymmetric dissociation channels is observed, with a strong correlation between the projectile scattering angle and the molecular ion orientation. The measurements here provide clear evidence that projectiles distinguish each atom in the target and that electron capture from near-site atoms is favored. Monte Carlo calculations based on the classical over-the-barrier model, with dimer targets represented as two independent atoms, are compared to the data. They give new insight into the dynamics of the collision by providing, for the different electron capture channels, the two-dimensional probability maps p(b), where b is the impact parameter vector in the molecular frame.
The trapping lasers of a magneto-optical trap have been used to bring Rb atoms into well defined oriented states. Coupled to recoil-ion-momentum spectroscopy, this provided a unique MOTRIMS setup ...which was able to probe scattering dynamics, including the coherence features, with unprecedented resolution. The technique was applied to the low-energy charge exchange reactions Na+ + Rb(5p±1)→Na(3p,4s)+Rb+. The measurements revealed detailed features of the collisional interaction which were employed to improve the theoretical description. As such, it was possible to ascertain the validity of the intuitive models used to predict the most likely capture transitions.
Synopsis Electron capture processes for low energy Ar9+ ions colliding on argon dimer targets are investigated, focusing attention on charge sharing between the two argon atoms as a function of the ...molecular orientation and the impact parameter. Confrontation between experimental results and MC-COBM simulations have been investigated to provide access to atomic site sensitivity of the different fragmentation processes by measuring the angular correlation between the scattered projectile and the recoiling fragments.
Synopsis Low energy collisions between ions and neon dimers are investigated, focusing attention on the dissociation of the ionized molecular target. The results show a clear dependance of the ...processes with the projectile charge state and an unexpected appearance of inner-shell single electron capture from one site of the neon dimer leading to interatomic coulombic decay process and low energy electrons emission.
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