TY - JOUR AU - Roman Chapurin AU - Xin Xie AU - Michael Van de Graaff AU - Jared Popowski AU - Jose D'Incao AU - Paul Julienne AU - Jun Ye AU - Eric Cornell AB - We perform precise studies of two- and three-body interactions near an intermediate-strength Feshbach resonance in 39K at 33.5820(14) G. Precise measurement of dimer binding energies, spanning three orders of magnitude, enables the construction of a complete two-body coupled-channel model for determination of the scattering lengths with an unprecedented low uncertainty. Utilizing an accurate scattering length map, we measure the precise location of the Efimov ground state to test van der Waals universality. Precise control of the sample's temperature and density ensures that systematic effects on the Efimov trimer state are well understood. We measure the ground Efimov resonance location to be at -14.05(17) times the van der Waals length rvdW, significantly deviating from the value of -9.7rvdW predicted by van der Waals universality. We find that a refined multichannel three-body model, built on our measurement of two-body physics, can account for this difference and even successfully predict the Efimov inelasticity parameter η. BT - Physical Review Letters DA - 2019-12 DO - 10.1103/PhysRevLett.123.233402 N2 - We perform precise studies of two- and three-body interactions near an intermediate-strength Feshbach resonance in 39K at 33.5820(14) G. Precise measurement of dimer binding energies, spanning three orders of magnitude, enables the construction of a complete two-body coupled-channel model for determination of the scattering lengths with an unprecedented low uncertainty. Utilizing an accurate scattering length map, we measure the precise location of the Efimov ground state to test van der Waals universality. Precise control of the sample's temperature and density ensures that systematic effects on the Efimov trimer state are well understood. We measure the ground Efimov resonance location to be at -14.05(17) times the van der Waals length rvdW, significantly deviating from the value of -9.7rvdW predicted by van der Waals universality. We find that a refined multichannel three-body model, built on our measurement of two-body physics, can account for this difference and even successfully predict the Efimov inelasticity parameter η. PY - 2019 EP - 233402 T2 - Physical Review Letters TI - Precision Test of the Limits to Universality in Few-Body Physics UR - https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.123.233402 VL - 123 SN - 0031-9007 ER -