Magnetic fields in heavy ion collisions : flow and charge transport
Inghirami, G., Mace, M., Hirono, Y., Del Zanna, L., Kharzeev, D. E., & Bleicher, M. (2020). Magnetic fields in heavy ion collisions : flow and charge transport. European Physical Journal C, 80(3), Article 293. https://doi.org/10.1140/epjc/s10052-020-7847-4
Published inEuropean Physical Journal C
© The Author(s) 2020
At the earliest times after a heavy-ion collision, the magnetic field created by the spectator nucleons will generate an extremely strong, albeit rapidly decreasing in time, magnetic field. The impact of this magnetic field may have detectable consequences, and is believed to drive anomalous transport effects like the Chiral Magnetic Effect (CME). We detail an exploratory study on the effects of a dynamical magnetic field on the hydrodynamic medium created in the collisions of two ultrarelativistic heavy-ions, using the framework of numerical ideal MagnetoHydroDynamics (MHD) with the ECHO-QGP code. In this study, we consider a magnetic field captured in a conducting medium, where the conductivity can receive contributions from the electromagnetic conductivity σ and the chiral magnetic conductivity σχ. We first study the elliptic flow of pions, which we show is relatively unchanged by the introduction of a magnetic field. However, by increasing the magnitude of the magnetic field, we find evidence for an enhancement of the elliptic flow in peripheral collisions. This effect is stronger at RHIC than the LHC, and it is evident already at intermediate collision centralities. Next, we explore the impact of the chiral magnetic conductivity on electric charges produced at the edges of the fireball. This initial σχ can be understood as a long-wavelength effective description of chiral fermion production. We then demonstrate that this chiral charge, when transported by the MHD medium, produces a charge dipole perpendicular to the reaction plane which extends a few units in rapidity. Assuming charge conservation at the freeze-out surface, we show that the produced charge imbalance can have measurable effects on some experimental observables, like v1 or ⟨sinϕ⟩. This demonstrates the ability of a MHD fluid to transport the signature of the initial chiral magnetic fields to late times. We also comment on the limitations of the ideal MHD approximation and detail how further development of a dissipative-resistive model can provide a more realistic description of the QGP. ...
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Related funder(s)Academy of Finland
Funding program(s)Academy Project, AoF
Additional information about fundingG. Inghirami is supported by the Academy of Finland, Project no. 297058. MM is supported by the European Research Council, grant ERC-2015-CoG-681707. This material is based on work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics, under Contracts No. DE-SC0012704 (D.K, Y.H, and M.M.) and No. DE-FG02-88ER40388 (D.K., M.M.), and within the framework of the Beam Energy Scan Theory (BEST) Topical Collaboration. The work of Y.H. was supported in part by the Korean Ministry of Education, Science and Technology, Gyeongsangbuk-do and Pohang City for Independent Junior Research Groups at the Asia Pacific Center for Theoretical Physics. During the initial parts of this work, M. Mace was supported by the BEST Topical Collaboration. During the initial part of this work, G. Inghirami was supported by a GSI scholarship in cooperation with the John von Neumann Institute for Computing. G. Inghirami also gratefully acknowledges past support from the HIC for FAIR and from Helmholtz Graduate School for Hadron and Ion Research. This project was supported by COST Action CA15213 “THOR”. The computational resources were provided by the by the Center for Scientific Computing (CSC) of the Goethe University, the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231, by the INFN - Sezione di Firenze and by the Frankfurt Institute for Advanced Studies. Moreover, we acknowledge grants of computer capacity from the Finnish Grid and Cloud Infrastructure (persistent identifier urn:nbn:fi:research-infras-2016072533 ). ...
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