Pair Correlations and the Condensate Fraction in SuperfluidHe4

By applying the method of Hyland, Rowlands, and Cummings to pair-correlation functions obtained from new high-accuracy neutron-diffraction measurements, the condensate fraction, $n_0$, in superfluid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ has been determined for seven temperatures in the range $1.00<~T<~2.15$ K. The results are very well described by the relation $n_0\mathrm{}\left(T\right)=n_0\mathrm{}\left(0\right)[1-{\left(\frac{T}{T_{\lambda }}\right)}^{\alpha }]$, with $n_0\mathrm{}\left(0\right)=0.133\mathrm{}\pm 0.012$ and $\alpha =6.2\mathrm{}\pm 1.6$.