Abstract
Initial large global angular momentum in non-central relativistic heavy-ion collisions can produce strong vorticity, and through the spin-orbit coupling, causes the spin of particles to align with the system’s global angular momentum. We present the azimuthal angle dependent (relative to the reaction plane) polarization for Λ and Λ in mid-central Au+Au collisions at [see formula in PDF] = 200 GeV. We also present the ϕ meson spin alignment parameter, ρ00 in Au+Au collisions at [see formula in PDF] = 19.6, 27, 39, 62.4 and 200 GeV. The implications of the results are discussed.
Highlights
High-energy relativistic heavy-ion collisions at Relativistic Heavy Ion Collider (RHIC) produce a strongly interacting, hot and dense medium known as Quark Gluon Plasma (QGP) [1]
The initial orbital angular momentum, associated with the receding spectators, is large (∼1000 ) in non-central collisions may be transferred to quarks through spin-orbit coupling [2,3,4], which is transmitted to final-state hadrons and is detectable through the Λ(Λ) polarization and φ meson spin alignment
Measurements of the polarization of the particles produced in heavy-ion collisions can provide new insights into the initial conditions and evolution of the QGP [5, 6]
Summary
High-energy relativistic heavy-ion collisions at Relativistic Heavy Ion Collider (RHIC) produce a strongly interacting, hot and dense medium known as Quark Gluon Plasma (QGP) [1]. The STAR experiment at RHIC has observed for the first time a significant alignment between the angular momentum of the medium produced in non-central collision and the spin of Λ(Λ) hyperons (J=1/2), revealing that the matter produced in heavy-ion collisions is by far the most vortical system ever observed [7]. Such vorticity is expected to be maximal at the equator and due to the low viscosity of the system the vorticity may not be efficiently propagated to the poles. The φ meson spin alignment probes the particle production mechanisms
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