Charged elliptic flow at zero charge asymmetry
PublisherAmerican Physical Society
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The difference between the flow ellipticities of oppositely charged pions Delta nu(2) equivalent to nu(2)[pi(-)] -nu(2)[pi(+)], measured recently by the STAR Collaboration at the Brookhaven National Laboratory Relativistic Heavy Ion Collider (RHIC) shows a linear dependence on the event charge asymmetry A(+/-) = (N+ - N-)/(N+ + N-): Delta nu(2)(A(+/-)) = Delta nu(2)(0) + rA(+/-) with a slope r > 0 and a nonzero intercept Delta nu(2)(0) > 0 on the order of 10-4. We discuss two novel mechanisms, which could explain the nonzero value of the charged elliptic flow Delta nu(2) at zero charge asymmetry A(+/-) = 0, i.e., the nonzero positive intercept Delta nu(2)(0). Both effects are due to the electric fields created by the colliding ions. These fields have quadrupole asymmetry of the magnitude and the sign needed to account for the nonzero intercept Delta nu(2)(0) > 0 in the RHIC data. One of the mechanisms also involves the chiral magnetic effect. This mechanism, although negligible at RHIC energies, may become important at the CERN Large Hadron Collider energies.