The spectral slope of strong MHD turbulence has recently been a matter of controversy .
While Goldreich-Sridhar model ( 1995 ) predicts Kolmogorov ’ s -5/3 slope of turbulence , shallower slopes were often reported by numerical studies .
We argue that earlier numerics was affected by driving due to a diffuse locality of energy transfer in MHD case .
Our highest-resolution simulation ( 3072 ^ { 2 } \times 1024 ) has been able to reach the asymptotic -5 / 3 regime of the energy slope .
Additionally , we found that so-called dynamic alignment , proposed in the model with -3/2 slope , saturates and therefore can not affect asymptotic slope .
The observation of the asymptotic regime allowed us to measure Kolmogorov constant C _ { KA } = 3.2 \pm 0.2 for purely Alfvénic turbulence and C _ { K } = 4.1 \pm 0.3 for full MHD turbulence .
These values are much higher than the hydrodynamic value of 1.64 .
The larger value of Kolmogorov constant is an indication of a fairly inefficient energy transfer and , as we show in this Letter , is in theoretical agreement with our observation of diffuse locality .
We also explain what has been missing in numerical studies that reported shallower slopes .