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Title: Global hyperon polarization at local thermodynamic equilibrium with vorticity, magnetic field, and feed-down

Authors:
; ; ; ;
Publication Date:
Sponsoring Org.:
USDOE
OSTI Identifier:
1355964
Grant/Contract Number:
FG02-92ER-40713
Resource Type:
Journal Article: Publisher's Accepted Manuscript
Journal Name:
Physical Review C
Additional Journal Information:
Journal Volume: 95; Journal Issue: 5; Related Information: CHORUS Timestamp: 2017-05-05 22:11:17; Journal ID: ISSN 2469-9985
Publisher:
American Physical Society
Country of Publication:
United States
Language:
English

Citation Formats

Becattini, Francesco, Karpenko, Iurii, Lisa, Michael Annan, Upsal, Isaac, and Voloshin, Sergei A. Global hyperon polarization at local thermodynamic equilibrium with vorticity, magnetic field, and feed-down. United States: N. p., 2017. Web. doi:10.1103/PhysRevC.95.054902.
Becattini, Francesco, Karpenko, Iurii, Lisa, Michael Annan, Upsal, Isaac, & Voloshin, Sergei A. Global hyperon polarization at local thermodynamic equilibrium with vorticity, magnetic field, and feed-down. United States. doi:10.1103/PhysRevC.95.054902.
Becattini, Francesco, Karpenko, Iurii, Lisa, Michael Annan, Upsal, Isaac, and Voloshin, Sergei A. 2017. "Global hyperon polarization at local thermodynamic equilibrium with vorticity, magnetic field, and feed-down". United States. doi:10.1103/PhysRevC.95.054902.
@article{osti_1355964,
title = {Global hyperon polarization at local thermodynamic equilibrium with vorticity, magnetic field, and feed-down},
author = {Becattini, Francesco and Karpenko, Iurii and Lisa, Michael Annan and Upsal, Isaac and Voloshin, Sergei A.},
abstractNote = {},
doi = {10.1103/PhysRevC.95.054902},
journal = {Physical Review C},
number = 5,
volume = 95,
place = {United States},
year = 2017,
month = 5
}

Journal Article:
Free Publicly Available Full Text
This content will become publicly available on May 5, 2018
Publisher's Accepted Manuscript

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  • The extreme energy densities generated by ultra-relativistic collisions between heavy atomic nuclei produce a state of matter that behaves surprisingly like a fluid, with exceptionally high temperature and low viscosity. Non-central collisions have angular momenta of the order of 1,000ћ, and the resulting fluid may have a strong vortical structure that must be understood to describe the fluid properly. The vortical structure is also of particular interest because the restoration of fundamental symmetries of quantum chromodynamics is expected to produce novel physical effects in the presence of strong vorticity. But, no experimental indications of fluid vorticity in heavy ion collisionsmore » have yet been found. Since vorticity represents a local rotational structure of the fluid, spin–orbit coupling can lead to preferential orientation of particle spins along the direction of rotation. Here we present measurements of an alignment between the global angular momentum of a non-central collision and the spin of emitted particles (in this case the collision occurs between gold nuclei and produces Λ baryons), revealing that the fluid produced in heavy ion collisions is the most vortical system so far observed. (At high energies, this fluid is a quark–gluon plasma.) We find that Λ and hyperons show a positive polarization of the order of a few per cent, consistent with some hydrodynamic predictions. (A hyperon is a particle composed of three quarks, at least one of which is a strange quark; the remainder are up and down quarks, found in protons and neutrons.) A previous measurement that reported a null result, that is, zero polarization, at higher collision energies is seen to be consistent with the trend of our observations, though with larger statistical uncertainties. Furthermore, these data provide experimental access to the vortical structure of the nearly ideal liquid created in a heavy ion collision and should prove valuable in the development of hydrodynamic models that quantitatively connect observations to the theory of the strong force.« less
  • It has recently been reported that two types of triaxial electric or magnetic fields can drive vorticity in dielectric or magnetic particle suspensions, respectively. The first type-symmetry -- breaking rational fields -- consists of three mutually orthogonal fields, two alternating and one dc, and the second type -- rational triads -- consists of three mutually orthogonal alternating fields. In each case it can be shown through experiment and theory that the fluid vorticity vector is parallel to one of the three field components. For any given set of field frequencies this axis is invariant, but the sign and magnitude ofmore » the vorticity (at constant field strength) can be controlled by the phase angles of the alternating components and, at least for some symmetry-breaking rational fields, the direction of the dc field. In short, the locus of possible vorticity vectors is a 1-d set that is symmetric about zero and is along a field direction. In this paper we show that continuous, 3-d control of the vorticity vector is possible by progressively transitioning the field symmetry by applying a dc bias along one of the principal axes. Such biased rational triads are a combination of symmetry-breaking rational fields and rational triads. A surprising aspect of these transitions is that the locus of possible vorticity vectors for any given field bias is extremely complex, encompassing all three spatial dimensions. As a result, the evolution of a vorticity vector as the dc bias is increased is complex, with large components occurring along unexpected directions. More remarkable are the elaborate vorticity vector orbits that occur when one or more of the field frequencies are detuned. As a result, these orbits provide the basis for highly effective mixing strategies wherein the vorticity axis periodically explores a range of orientations and magnitudes.« less