The global polarization of {\Lambda} hyperons along the total orbital angular momentum of a relativistic heavy-ion collision is presented based on the high statistics data samples collected in Au+Au ...collisions at \sqrt{s_{NN}} = 2.4 GeV and Ag+Ag at 2.55 GeV with the High-Acceptance Di-Electron Spectrometer (HADES) at GSI, Darmstadt. This is the first measurement below the strangeness production threshold in nucleon-nucleon collisions. Results are reported as a function of the collision centrality as well as a function of the hyperon transverse momentum (p_T) and rapidity (y_{CM}) for the range of centrality 0--40%. We observe a strong centrality dependence of the polarization with an increasing signal towards peripheral collisions. For mid-central (20--40%) collisions the polarization magnitudes are <P_{\Lambda}>(%) = 6.8 \pm 1.3 (stat.) \pm 2.1 (syst.) for Au+Au and <P_{\Lambda}>(%) = 6.2 \pm 0.4 (stat.) \pm 0.6 (syst.) for Ag+Ag, which are the largest values observed so far. This observation thus provides a continuation of the increasing trend previously observed by STAR and contrasts expectations from recent theoretical calculations predicting a maximum in the region of collision energies about 3 GeV. The observed polarization is of a similar magnitude as predicted by 3D fluid dynamics and the UrQMD plus thermal vorticity model and significantly above results from the AMPT model.
Second-harmonic microscopy is a fast, interface specific remote sensing technique for the quantitative in situ characterization of a large variety of real interfaces. The second-order optical ...susceptibility tensor of the individual domains in an image can be measured and interpreted molecularly. Additional information as compared with linear optical microscopy is obtained. A noncollinear experimental geometry with no linear optical analogue combines various outstanding advantages.
Second-harmonic microscopy (SHM) is a fast, non-contact, surface-sensitive imaging technique for the quantitative
in situ characterisation of a large variety of real interfaces. In conventional ...second-harmonic generation (SHG) experiments the surface symmetry and order averaged over the illuminated area are obtained. In contrast, SHM allows us to measure the susceptibility of any feature resolved in the images. The local susceptibility can be interpreted in terms of local molecular order and symmetry. The resolution limit of the stigmatic microscope is Abbe's limit for the frequency-doubled light.
