May 13 – 19, 2018
Venice, Italy
Europe/Zurich timezone
The organisers warmly thank all participants for such a lively QM2018! See you in China in 2019!

Lambda polarization in heavy ion collisions: from RHIC BES to LHC energies

May 15, 2018, 9:40 AM
Sala Mosaici-2, 3rd Floor (Palazzo del Casinò)

Sala Mosaici-2, 3rd Floor

Palazzo del Casinò

Parallel Talk Chirality, vorticity and polarisation effects Chirality, vorticity and polarisation effects


Dr Iurii Karpenko (SUBATECH Nantes)


In hydrodynamic picture of heavy ion collisions, local thermal vorticity of the QGP fluid leads to polarization of nonzero spin hadrons produced out of it [1]. The nonzero polarization of $\Lambda$ hyperons has been recently discovered by STAR in non-central Au-Au collisions in RHIC Beam Energy Scan program [2].

We further study the predictions of the hydrodynamic model for different components of the $\Lambda$ polarization in the framework of 3-dimensional viscous hydrodynamic model with UrQMD initial state, and demonstrate that:

  1. at RHIC Beam Energy Scan energies, the global polarization $P$ of produced Lambda is directed along the total angular momentum of the fireball (perpendicular to reaction plane). $P$ decreases with collision energy from 1.7 to 0.2% [3], in agreement with STAR results [2]. The global $\Lambda$ polarization further decreases towards LHC energies,

  2. at full RHIC and LHC energies, the dominant component of polarization is the one in the beam direction. This component has a quadrupole structure in transverse momentum plane. Its amplitude $f_2$ shows a mild decrease with collision energy, and it is thus detectable at LHC enegries.

We show that different components of polarization are driven by different properties of the hydrodynamic expansion: whereas the global polarization $P$ is a result of initial shear flow in the reaction plane, $f_2$ is driven by anisotropy of the transverse expansion (which is also responsible for elliptic flow $v_2$). Polarization component in the beam direction is a generic effect present even in a simple 2-dimensional hydrodynamic calculation with longitudinal boost invariance [4].

[1] F. Becattini, V. Chandra, L. Del Zanna, E. Grossi, Ann. Phys. 338 (2013) 32.
[2] STAR collaboration, Nature 548 (2017), 62–65
[3] I. Karpenko, F. Becattini, Eur. Phys. J. C (2017) 77: 213.
[4] F. Becattini, Iu. Karpenko, arXiv:1707.07984, accepted to Phys.Rev.Lett.

Content type Theory
Centralised submission by Collaboration Presenter name already specified

Primary author

Dr Iurii Karpenko (SUBATECH Nantes)


Francesco Becattini (Unversity of Florence)

Presentation materials