Collisional Frequency Shifts in 133Cs Fountain Clocks
P J. Leo, Paul S. Julienne, F H. Mies, Carl J. Williams
We present a theoretical analysis of the pressure shift in Cs fountain clocks using the highly constrained binary collision model described by Leo et al. [Phys. Rev. Lett. xx, xx (2000)]. We predict a reversal in the pressure shift at temperatures near 0.08 K which could allow elimination of a large source of uncertainty in the Cs fountain clock. Our results show that s-waves dominate the collision process however as a consequence of the large scattering lengths in Cs the pressure shift is strongly temperature dependent and does not reach a constant Wigner-law value until temperatures are less than 0.1 nK.