6 research outputs found
Measurement of global polarization of {\Lambda} hyperons in few-GeV heavy-ion collisions
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 (%) = 6.0 \pm 1.3
(stat.) \pm 2.0 (syst.) for Au+Au and (%) = 4.6 \pm 0.4 (stat.)
\pm 0.5 (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.Comment: 8 pages, 4 figure
The synthesis and non-linear optical properties of (N-alkylpyrrol-2-yl)squaraine derivatives. Part 1
The synthesis of a soluble poly(pyrrolylsquaraine) was achieved by N-alkylation of the pyrrole nucleus with 1-bromooctadecane and subsequent condensation with squaric acid. Bis(1-octadecylpyrrol-2-yl)-squaraine was also produced and found to exist in a variety of inseparable isomeric forms. When deposited as Langmuir-Blodgett monolayers on hydrophilic substrates, these dyes exhibit second harmonic generation (SHG) with d = 0.5 ± 0.1 pm V for both. For comparison, bis(3,5-dimethyl-1-octadecylpyrrol-2-yl)squaraine was synthesised and revealed a higher SHG activity of d = 1.8 ± 0.2 pm V. Poly(1-octadecylpyrrolylsquaraine) is the first alternating donor-acceptor polymer to give SHG
Measurement of global polarization of hyperons in few-GeV heavy-ion collisions
The global polarization of Λ 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 √({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 (%) = 6.0 \pm 1.3 (stat.) \pm 2.0 (syst.) for Au+Au and (%) = 4.6 \pm 0.4 (stat.) \pm 0.5 (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
Measurement of global polarization of hyperons in few-GeV heavy-ion collisions
The global polarization of Λ 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 = 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's 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 \left (%) = 6.8 1.3 (stat.) 2.1 (syst.) for Au+Au and \left (%) = 6.2 0.4 (stat.) 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