Ultra-relativistic nuclear collisions: where the spectators flow?

Abstract

In high energy heavy ion collisions, the directed flow of particles is conventionally measured with respect to that of the projectile spectators, which is defined as positive $x$ direction. But it is not known if the spectators deflect in the "outward" direction or "inward" -- toward the center line of the collision. In this Letter we discuss how the measurements of the directed flow at mid-rapidity, especially in asymmetric collision such as Cu+Au, can be used to answer this question. We show that the existing data strongly favor the case that the spectators, in the ultrarelativistic collisions, on average deflect outwards.

4 pages, 4 figures, typos corrected, added grid to Fig.4

References in corpus (5)

• Triangularity and Dipole Asymmetry in Heavy Ion Collisions
• Global polarization measurement in Au+Au collisions
• Testing the Chiral Magnetic Effect with Central U+U collisions
• Polarized secondary particles in unpolarized high energy hadron-hadron collisions?
• Beam Fragmentation in Heavy Ion Collisions with Realistically Correlated Nuclear Configurations

Cited by in corpus (10)

• Global $\Lambda$ hyperon polarization in nuclear collisions: evidence for the most vortical fluid
• Global polarization of $\Lambda$ hyperons in Au+Au collisions at $\sqrt{s_{{}_{NN}}}$ = 200 GeV
• Global hyperon polarization at local thermodynamic equilibrium with vorticity, magnetic field and feed-down
• Global polarization of $\Xi$ and $\Omega$ hyperons in Au+Au collisions at $\sqrt{s_{{}_{NN}}}$ = 200 GeV
• Vorticity and particle polarization in heavy ion collisions (experimental perspective)
• Polarization phenomenon in heavy-ion collisions
• Azimuthal anisotropy in Cu+Au collisions at $\sqrt{s_{{}_{NN}}}$ = 200 GeV
• Charge-dependent directed flow in Cu+Au collisions at $\sqrt{s_{{}_{NN}}}$ = 200 GeV
• Testing the impact of electromagnetic fields on the directed flow of constituent quarks in heavy-ion collisions
• Elliptic flow of charged particles at midrapidity relative to the spectator plane in Pb-Pb and Xe-Xe collisions