Charge balance functions and the transverse flow

Correlations between opposite charge particles emitted in ultrarelativistic heavy-ion collisions can be used as a measure of the transverse flow present at the time of the decoupling of the charged pair. The width of the charge balance function in azimuthal angle depends on the transverse velocity and the temperature of the emitting source. Asymmetry in the balance function between in plane and out of plane emission can serve as a probe of the azimuthal asymmetry of the velocity field in the source.