The effect of carrier envelope phase (CEP) on the spatio-temporal
distribution of the electron-positron pairs created by untraintense
counterpropagating femtosecond laser pulses is studied. When the laser pulses
are linearly polarized, the temporal distribution of the pairs is found to be
sensitive to CEP. On the hand, it is found to be largely insensitive to CEP for
circularly polarized pulses.Comment: 18 pages, 12 figures. Submitted to The European Physical Journal D
(EPJ D