CONDENSATE AND FINAL-STATE EFFECTS IN SUPERFLUID HE-4

We present high-precision measurements of the dynamics of single atoms in superfluid He-4 at T=1.6 K and saturated vapor pressure. The measu rements were taken on the MARI instrument at the ISIS neutron-scatteri ng facility, Rutherford-Appleton Laboratory. From the measurements we obtain a condensate fraction n(0)=6.0 +/- 2.0%, at T=1.6 K, The final- state effects (FSE's) in the atomic response are also determined from the data in the form of a final-state broadening function, R(Q,y). We find that this FS function is the same in the superfluid at T=1.6 It a s that determined previously in normal He-4 at T=2.3 K. If we reanalyz e the data assuming that the superfluid has no condensate, i.e., n(0)= 0, then the data requires that the normal n(k) change dramatically bet ween T=2.3 K and T=1.6 K. Since such a change in n(k) is physically un expected, given that kT is much less than the zero-point energy, the d ata requires that a new contribution, such as a condensate,enter n(k i n the superfluid.