Lambda polarization in 108Ag<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.svg"><mml:mo linebreak="badbreak" linebreakstyle="after">+</mml:mo><mml:msup><mml:mrow/><mml:mrow><mml:mn>108</mml:mn></mml:mrow></mml:msup></mml:math>Ag and 197Au<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si2.svg"><mml:mo linebreak="badbreak" linebreakstyle="after">+</mml:mo><mml:msup><mml:mrow/><mml:mrow><mml:mn>197</mml:mn></mml:mrow></mml:msup></mml:math>Au collisions around a few GeV
Xian-Gai Deng, Xu-Guang Huang, Y. G.
Abstract
Within the framework of Ultra-relativistic Quantum Molecular Dynamics (UrQMD) model, we extract the global spin polarization of Λ hyperon in 108Ag+108Ag and 197 Au+197Au collisions at sNN=2.42–62.4 GeV. We use two different approaches to calculate the Λ polarization Py: approach I is based on equilibrium assumption so that Py is determined by thermal vorticity and approach II assumes a proportional relation between Py and the system's angular momentum in Λ's rest frame. We find that both approaches can describe the experimental data at low energies around a few GeV but only approach I describes well also higher-energy data. This suggests that at higher energies the relativistic effect plays an important role. After taking into such effect properly, the relativity-improved approach II can describe the higher-energy data as well.