  We present blast wave fits to elliptic flow ($v_{2}(p_{\rm T})$) data in
minimum bias collisions from the $\sqrt{s_{\rm NN}} =$ 7.7--200 GeV at RHIC,
and 2.76 TeV at LHC. The fits are performed separately for particles and
corresponding anti-particles. The mean transverse velocity parameter $\beta$
shows an energy dependent difference between particles and corresponding
anti-particles, which increases as the beam energy decreases. Possible effects
of feed down, baryon stopping, anti-particle absorption, and early production
times for anti-particles are discussed.
