  The interference between the K+K- S-wave and P-wave amplitudes in B_s ->
J/psi K+K- decays with the K+K- pairs in the region around the phi(1020)
resonance is used to determine the variation of the difference of the strong
phase between these amplitudes as a function of K+K- invariant mass. Combined
with the results from our CP asymmetry measurements in B_s -> J/psi phi decays,
we conclude that the B_s mass eigenstate that is almost CP =+1 is lighter and
decays faster than the mass eigenstate that is almost CP =-1. This determines
the sign of the decay width difference DeltaGamma_s == Gamma_L -Gamma_H to be
positive. Our result also resolves the ambiguity in the past measurements of
the CP violating phase phi_s to be close to zero rather than pi. These
conclusions are in agreement with the Standard Model expectations.
