Global Lambda hyperon polarization in nuclear collisions

doi:10.1038/nature23004

CORC > 上海应用物理研究所 > 中国科学院上海应用物理研究所 > 中科院上海应用物理研究所2011-2017年

	Global Lambda hyperon polarization in nuclear collisions
	Adamczyk, L; Adkins, JK; Agakishiev, G; Aggarwal, MM; Ahammed, Z; Ajitanand, NN; Alekseev, I; Anderson, DM; Aoyama, R; Aparin, A
刊名	NATURE
	2017
卷号	548 期号:7665 页码:62-+
关键词	Heavy-ion Collisions Vorticity
ISSN号	0028-0836
DOI	10.1038/nature23004
文献子类	期刊论文
英文摘要	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(1). Non-central collisions have angular momenta of the order of 1,000., and the resulting fluid may have a strong vortical structure(2-4) 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(5). However, no experimental indications of fluid vorticity in heavy ion collisions 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 Lambda 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 Lambda and (Lambda) over bar hyperons show a positive polarization of the order of a few per cent, consistent with some hydrodynamic predictions(6). (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(7) 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. These data provide experimental access to the vortical structure of the nearly ideal liquid(8) 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.
WOS关键词	HEAVY-ION COLLISIONS ; VORTICITY
语种	英语
WOS记录号	WOS:000406831700036
内容类型	期刊论文
源URL	[http://ir.sinap.ac.cn/handle/331007/28669]
专题	上海应用物理研究所_中科院上海应用物理研究所2011-2017年
推荐引用方式 GB/T 7714	Adamczyk, L,Adkins, JK,Agakishiev, G,et al. Global Lambda hyperon polarization in nuclear collisions[J]. NATURE,2017,548(7665):62-+.
APA	Adamczyk, L.,Adkins, JK.,Agakishiev, G.,Aggarwal, MM.,Ahammed, Z.,...&Zyzak, M.(2017).Global Lambda hyperon polarization in nuclear collisions.NATURE,548(7665),62-+.
MLA	Adamczyk, L,et al."Global Lambda hyperon polarization in nuclear collisions".NATURE 548.7665(2017):62-+.