Beam-Energy Dependence of the Directed Flow of Protons, Antiprotons, and Pions in Au+Au Collisions

Abstract

Rapidity-odd directed flow (v1) measurements for charged pions, protons and antiprotons near mid-rapidity (y = 0) are reported in

Beam-Energy Dependence of Directed Flow ofΛ,Λ¯,K±,Adamczyk1, Adams2, Adkins3 et al. 2018Phys. Rev. Lett.Self Cite862270View full textAdd to dashboardCite

“…The pattern of departure from a coalescence-inspired sum rule can be a valuable new tool for probing the collision dynamics. [7]. Based on hydrodynamic calculations [8,9], a minimum in directed flow has been proposed as a signature of a first-order phase transition between hadronic matter and quark-gluon plasma.…”

“…The assumption of purely hadronic physics is disfavored, but there is no consensus on whether STAR measurements [7] favor a crossover or first-order phase transition. Models do not produce any dv 1 =dy minimum over the observed energy range [10][11][12][13][14]16], with the exception of one case where a minimum was calculated near one third of the energy of the measured minimum [15].…”

“…The centrality was determined from the number of charged particles within jηj < 0.5. For determination of the event plane [1], two beam-beam counters (pseudorapidity coverage 3.3 < jηj < 5.0 for inner tiles) were used at ffiffiffiffiffiffiffi ffi s NN p ≤ 39 GeV [7,28], while the STAR detector zero-degree calorimeter shower-maximum detectors (jηj > 6.3) were used at ffiffiffiffiffiffiffi ffi s NN p ¼ 62.4 and 200 GeV [7,[29][30][31][32]. We require the primary vertex position of each event along the beam direction to lie within 70 cm of the center of the detector at ffiffiffiffiffiffiffi ffi s NN p ¼ 7.7 GeV, within 50 cm at 11.5-27 GeV, and within 40 cm at 39-200 GeV.…”

Does non-monotonic behavior of directed flow signal the onset of deconfinement?

“…In Fig. 2, we compare proton directed flow to the STAR data for mid-central Au+Au collisions [10]. It is seen that the effect of nuclear cluster formation on the proton v 1 is about 15%, and the effect of the statistical decay of nuclear cluster is very tiny.…”

“…The theoretical studies on the beam energy dependence of the directed flow based on the newly developed models such as hybrid transport approach [7], three fluid model [8], and the PHDS transport model [9] have been extensively performed. However, a definite conclusion has not been drawn so far as to the interpretation of the directed flow data measured by the STAR collaboration [10].…”