Background thermal contributions in testing the Unruh effect.

Park et al's recent comment that for detectors with large energy gap in comparison with the temperature of the background thermal bath, the maximum excitation rate is obtained for some non-zero detector's velocity is correct but was previously discussed by ourselves in [3], and does not affect in [2] any mathematical formula, numerical result, or our final conclusion that the background thermal bath does not contribute substantially in the depolarization of electrons at LEP. 1 Park et al's comment [1] that for detectors with large energy gap ∆E in comparison with the temperature β −1 of the background thermal bath, one should not state that the faster a detector moves the less it interacts with the background thermal bath, because the maximum excitation rate is obtained for some detector's velocity v > 0, is true but does not affect in [2] any mathematical formula, numerical result, or our final conclusion that the background thermal bath does not contribute substantially in the depolarization of electrons at LEP. In fact, as calculated in Sec. IV of [2] using a two-level scalar model for the electron, the vacuum contribution to the flip probability is three orders of magnitude larger than the background thermal bath contribution, because of the electron acceleration.