Abstract
We first compare different approaches to estimates of the magnitude of the chiral magnetic effect in relativistic heavy ion collisions and show that their main difference lies in the assumptions on the length of persistence of the magnetic field generated by the colliding nuclei. We then analyze recent measurements of the global polarization of $\Lambda$ and $\bar \Lambda$ hyperons in terms of the bounds they set on the magnitude of the late time magnetic field.
Highlights
A few years ago, the claim that experimental data from the STAR Collaboration [1,2] could indicate a sizeable chiral magnetic effect (CME) [3,4] in peripheral heavy ion collisions initiated extensive theoretical and experimental research
Instead, based on a recent analysis of topological fluctuations in the glasma [10] we will reiterate the observation that the underlying physics is quite complicated, different approaches give similar results leading to the conclusion that whether or not phenomena related to the CME can be large enough to be observable in relativistic heavy ion collisions depends crucially on the longevity of the magnetic field
We have argued that different approaches to calculating the initial axial charge density fluctuations in the quark-gluon plasma created in heavy ion collisions yield estimates of similar magnitude
Summary
A few years ago, the claim that experimental data from the STAR Collaboration [1,2] could indicate a sizeable chiral magnetic effect (CME) [3,4] in peripheral heavy ion collisions initiated extensive theoretical and experimental research. By Gürsoy et al [12], the magnetic field may be partially “frozen in” by the large electric conductivity and the nonlinear properties of the quark gluon plasma Such a delayed decay could result in a significant magnetic field strength at midrapidity and late times. We point out that new limits on the difference in observed global Λ and Λpolarization transverse to the reaction plane in peripheral heavy ion collisions, a phenomenon that is at the focus of intense investigation in connection with the study of the quark gluon plasma vorticity [13,14,15], provides a relevant limit on the magnetic field strength at late times and a direct test for, e.g., the prediction made in [12].
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