Differential measurements of Λ polarization in Au plus Au collisions and a search for the magnetic field by STAR

Global hadron polarization, (P) over bar (H), was measured by the STAR collaboration through the Lambda hyperon, confirming the existence of extremely large vorticities within the Quark-Gluon Plasma (QGP). A recent study using high-statistics data set at root s(NN) = 200 GeV has shown that (P) over bar (H) depends on collision centrality, azimuthal angle, phi, transverse momentum, p(T), and pseudorapidity, eta. We extend these differential measurements to the collision energies of root s(NN) = 54.4 and 27 GeV, using three different detectors for the event-plane determination. Additionally, there is a suggested enhancement (P) over bar ((Lambda) over bar) relative to (P) over bar (Lambda) across all beam energies; however, the statistics are too limited to make a significant measurement. A recent, high-statistics data set of Au+Au collisions at root s(NN) = 27 GeV includes improved event-plane resolution; we discuss the feasibility of using this data set to study the possible splitting between (P) over bar (Lambda) and (P) over bar ((Lambda) over bar).

Automated summary

The measurement of global hadron polarization through Lambda hyperon by the STAR collaboration confirms the existence of extremely large vorticities within the Quark-Gluon Plasma. The polarization is found to depend on collision centrality, azimuthal angle, transverse momentum, and pseudorapidity. The study also explores the suggested enhancement of polarization relative to different beam energies, but limited statistics prevent significant measurements. Additionally, the feasibility of using high-statistics data set to study the possible splitting between different types of polarization is discussed.