Determination of the s-wave scattering length of chromium -: art. no. 193201

We have measured the deca-triplet s-wave scattering length of the bosonic chromium isotopes Cr-52 and Cr-50. From the time constants for cross-dimensional thermalization in ultracold atomic samples, we have determined the magnitudes \a(Cr-52)\=(170+/-39)a(0) and \a(Cr-50)\=(40+/-15)a(0), where a(0)=0.053 nm. By measuring the rethermalization rate of Cr-52 over a wide temperature range and comparing the temperature dependence with the effective-range theory and numerical single-channel calculations, we have obtained strong evidence that the sign of a(Cr-52) is positive. Rescaling our Cr-52 model potential to Cr-50 strongly suggests that a(Cr-50) is positive also.