title: Test of the universality of the three-body Efimov parameter at narrow Feshbach resonances.
abstract: We measure the critical scattering length for the appearance of the first three-body bound state, or Efimov three-body parameter, at seven different Feshbach resonances in ultracold ^{39}K atoms. We study both intermediate and narrow resonances, where the three-body spectrum is expected to be determined by the nonuniversal coupling of two scattering channels. Instead, our observed ratio of the three-body parameter with the van der Waals radius is approximately the same universal ratio as for broader resonances. This unexpected observation suggests the presence of a new regime for three-body scattering at narrow resonances.
authors: LENS and Dipartimento di Fisica e Astronomia, Universitá di Firenze, and Istituto Nazionale di Ottica, CNR, 50019 Sesto Fiorentino, Italy.
authors: Sanjukta
authors: S
authors: Roy
authors: Manuele
authors: M
authors: Landini
authors: Andreas
authors: A
authors: Trenkwalder
authors: Giulia
authors: G
authors: Semeghini
authors: Giacomo
authors: G
authors: Spagnolli
authors: Andrea
authors: A
authors: Simoni
authors: Marco
authors: M
authors: Fattori
authors: Massimo
authors: M
authors: Inguscio
authors: Giovanni
authors: G
authors: Modugno