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Title: Global polarization measurements and their implications regarding the magnetic fields

Spectators in non-central heavy-ion collisions create dynamic magnetic fields with magnitudes as large as $10^{14}$ Tesla. The fields may cause a splitting between $\Lambda$ and $\overline{\Lambda}$ polarization through magnetic moment coupling. A signal of such splitting could provide a quantitative estimate of the field strength at freeze-out. The dynamics of the magnetic field are expected to depend on the conductivity of the QGP. The field is of fundamental interest for heavy-ion physics, but is of particular interest to other novel phenomena, e.g. the Chiral Magnetic Effect (CME).

The STAR Collaboration observed global hyperon polarization in non-central Au+Au collisions in the energy range of 7.7 to 39 GeV [1]. In this analysis, a magnetic splitting is hinted at, but the improved statistics and resolution achievable with future runs are required to make a definitive measurement of the magnetic field. In 2018, RHIC will run an isobaric system (Zr+Zr and Ru+Ru) as well as 1B 27GeV Au+Au events. The 27GeV dataset will add an important point on the energy trend of the polarization, and may provide the earliest statistical evidence for magnetic splitting. If a measurable splitting existed at top RHIC energy for the isobar system, one would expect a difference in the splitting between the two species, due to a difference in the underlying magnetic field. Observing such a difference would provide robust evidence that the splitting between $\Lambda$ and $\overline{\Lambda}$ polarization is driven by the magnetic field.

[1] Nature 548, 62 (2017)
 

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(old) version 1
Title: Magnetic field implications and opportunities in global polarization measurements

Spectators in non-central heavy-ion collisions create dynamic magnetic fields with magnitude as large as $10^{14}$ Tesla. The field may cause a splitting between $\Lambda$ and $\overline{\Lambda}$ polarization through magnetic moment coupling. A signal of such splitting could provide a quantitative estimate of the field strength at freeze out. The dynamics of the magnetic field depend, in principal, on the conductivity of the QGP. The field is of fundamental interest to heavy-ion collisions, but is of particular interest to other novel phenomena, e.g. the Chiral Magnetic Effect (CME).

The STAR Collaboration has made the first observation of global hyperon polarization in non-central Au+Au collisions at Beam Energy Scan energies. A magnetic splitting is hinted at, but the improved statistics and resolution achievable with future runs are required to make a definitive measurement of the magnetic field. In 2018 RHIC will run an isobaric system (Zr+Zr and Ru+Ru) as well as 1B new 27GeV Au+Au events. The 27GeV dataset will add an important point on the energy trend of the polarization, and may provide the earliest statistical evidence for splitting. If a measurable splitting existed at top RHIC energy for the isobar system one would expect a difference in the splitting for the different species, due to a difference in the underlying magnetic field. Observing a difference in the isobar data would be an extremely robust measurement.

version 2

Title: Global polarization measurements and their implications regarding the magnetic fields

Spectators in non-central heavy-ion collisions create dynamic magnetic fields with magnitudes as large as $10^{14}$ Tesla. The fields may cause a splitting between $\Lambda$ and $\overline{\Lambda}$ polarization through magnetic moment coupling. A signal of such splitting could provide a quantitative estimate of the field strength at freeze out. The dynamics of the magnetic field are expected to depend, on the conductivity of the QGP. The field is of fundamental interest to heavy-ion collisions, but is of particular interest to other novel phenomena, e.g. the Chiral Magnetic Effect (CME).

The STAR Collaboration has made the first observation of global hyperon polarization in non-central Au+Au collisions in the energy range of 7.7 to 39 GeV. In this analysis, a magnetic splitting is hinted at, but the improved statistics and resolution achievable with future runs are required to make a definitive measurement of the magnetic field. In 2018, RHIC will run an isobaric system (Zr+Zr and Ru+Ru) as well as 1B 27GeV Au+Au events. The 27GeV dataset will add an important point on the energy trend of the polarization, and may provide the earliest statistical evidence for magnetic splitting. If a measurable splitting existed at top RHIC energy for the isobar system, one would expect a difference in the splitting for the different species, due to a difference in the underlying magnetic field. Observing a difference in the isobar data would be an extremely robust measurement.

 
version 3

Title: Global polarization measurements and their implications regarding the magnetic fields

Spectators in non-central heavy-ion collisions create dynamic magnetic fields with magnitudes as large as $10^{14}$ Tesla. The fields may cause a splitting between $\Lambda$ and $\overline{\Lambda}$ polarization through magnetic moment coupling. A signal of such splitting could provide a quantitative estimate of the field strength at freeze out. The dynamics of the magnetic field are expected to depend on the conductivity of the QGP. The field is of fundamental interest to heavy-ion collisions, but is of particular interest to other novel phenomena, e.g. the Chiral Magnetic Effect (CME).

The STAR Collaboration observed global hyperon polarization in non-central Au+Au collisions in the energy range of 7.7 to 39 GeV[1]. In this analysis, a magnetic splitting is hinted at, but the improved statistics and resolution achievable with future runs are required to make a definitive measurement of the magnetic field. In 2018, RHIC will run an isobaric system (Zr+Zr and Ru+Ru) as well as 1B 27GeV Au+Au events. The 27GeV dataset will add an important point on the energy trend of the polarization, and may provide the earliest statistical evidence for magnetic splitting. If a measurable splitting existed at top RHIC energy for the isobar system, one would expect a difference in the splitting between the two species, due to a difference in the underlying magnetic field. Observing such a different would provide a robust evidence that the splitting between $\Lambda$ and $\overline{\Lambda}$ polarization is driven by the magnetic field.

[1] Nature 548, 62 (2017)