title: Cancellation of the collisional frequency shift in caesium fountain clocks.
abstract: We have observed that the collisional frequency shift in primary caesium fountain clocks varies with the clock state population composition and, in particular, is zero for a given fraction of the |F=4,mF=0) atoms, depending on the initial cloud parameters. We present a theoretical model explaining our observations. The possibility of the collisional shift cancellation implies an improvement in the performance of caesium fountain standards and a simplification in their operation.
authors.affiliation: National Physical Laboratory, Hampton Road, Teddington, TW11 0LW, United Kingdom.
authors.forename: K
authors.initials: K
authors.lastname: Szymaniec
authors.forename: W
authors.initials: W
authors.lastname: Chałupczak
authors.forename: E
authors.initials: E
authors.lastname: Tiesinga
authors.forename: C J
authors.initials: CJ
authors.lastname: Williams
authors.forename: S
authors.initials: S
authors.lastname: Weyers
authors.forename: R
authors.initials: R
authors.lastname: Wynands