Abstract
The first measurement at the LHC of charge-dependent directed flow (v_{1}) relative to the spectator plane is presented for Pb-Pb collisions at sqrt[s_{NN}]=5.02 TeV. Results are reported for charged hadrons and D^{0} mesons for the transverse momentum intervals p_{T}>0.2 GeV/c and 3<p_{T}<6 GeV/c in the 5%-40% and 10%-40% centrality classes, respectively. The difference between the positively and negatively charged hadron v_{1} has a positive slope as a function of pseudorapidity η, dΔv_{1}/dη=[1.68±0.49(stat)±0.41(syst)]×10^{-4}. The same measurement for D^{0} and D[over ¯]^{0} mesons yields a positive value dΔv_{1}/dη=[4.9±1.7(stat)±0.6(syst)]×10^{-1}, which is about 3 orders of magnitude larger than the one of the charged hadrons. These measurements can provide new insights into the effects of the strong electromagnetic field and the initial tilt of matter created in noncentral heavy ion collisions on the dynamics of light (u, d, and s) and heavy (c)quarks. The large difference between the observed Δv_{1} of charged hadrons and D^{0} mesons may reflect different sensitivity of the charm and light quarks to the early time dynamics of a heavy ion collision. These observations challenge some recent theoretical calculations, which predicted a negative and an order of magnitude smaller value of dΔv_{1}/dη for both light flavor and charmed hadrons.
Highlights
Quantum chromodynamic (QCD) calculations on the lattice [1,2,3,4,5,6] predict at high temperatures the existence of a deconfined state of quarks and gluons, known as the quark– gluon plasma (QGP)
Characterizing the QGP properties is among the main goals of the experimental program with ultrarelativistic heavy ion collisions at the Large Hadron Collider (LHC)
Hadrons at the LHC [20] has significantly smaller magnitude compared to that at lower relativistic heavy ion collider (RHIC) energies [21], which can be interpreted as a smaller initial tilt at the LHC [22,23,24]
Summary
Quantum chromodynamic (QCD) calculations on the lattice [1,2,3,4,5,6] predict at high temperatures the existence of a deconfined state of quarks and gluons, known as the quark– gluon plasma (QGP). The measurements of the charge-integrated directed flow of hadrons containing light (u, d, and s) and heavy (c) quarks together with their difference in magnitude are of great interest and allow one to probe the three-dimensional space-time evolution of the produced matter.
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