We present measurements of $\pi^-$ and $\pi^+$ elliptic flow, $v_2$, at midrapidity in Au+Au collisions at $\sqrt{s_{_{\rm NN}}} =$ 200, 62.4, 39, 27, 19.6, 11.5 and 7.7 GeV, as a function of event-by-event charge asymmetry, $A_{ch}$, based on data from the STAR experiment at RHIC. We find that $\pi^-$ ($\pi^+$) elliptic flow linearly increases (decreases) with charge asymmetry for most centrality bins at $\sqrt{s_{_{\rm NN}}} = \text{27 GeV}$ and higher. At $\sqrt{s_{_{\rm NN}}} = \text{200 GeV}$, the slope of the difference of $v_2$ between $\pi^-$ and $\pi^+$ as a function of $A_{ch}$ exhibits a centrality dependence, which is qualitatively similar to calculations that incorporate a chiral magnetic wave effect. Similar centrality dependence is also observed at lower energies.
The distribution of observed charge asymmetry from STAR data.
Pion $v_2${2} as a function of observed charge asymmetry.
$v_2$ difference between $\pi^-$ and $\pi^+$ as a function of charge asymmetry with the tracking efficiency correction, for 30-40% central Au+Au collisions at 200 GeV. The errors are statistical only.
A supersymmetric extension of the interacting boson model (IBM) is constructed to describe high-spin anomalies in both even- and odd-mass spectra of the Hg, Pt region (190 ⩽ A ⩽ 200). Supergroup chains such as U ( 6 2j + 1 ) ⊃ Osp ( 6 2j + 1 ) ⊃ O (6) × Sp ( 6 2j + 1 )… U ( 6 2j + 1 ) ⊃ U ( 5 2j + 1 ) ⊃ Osp ( 5 2j + 1 )… incorporate a single j -shell fermion in addition to the usual “s” and “d” bosons ( L = 0 and L = 2). The orthosympletic supergroup reflects the strong pairing force in the subspace of the fermion intruder level. The model agrees favourably with experiment and microscopic calculation.
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