Context : The radio supernova remnant W50 hosts at its center the peculiar galactic X-ray binary SS 433 .
It shows a central spherical structure with two “ ears ” which are supposed to be formed by the interaction of the precessing jets of SS 433 with the supernova shell .

Aims : A study of the spectral and spatial structure of the X-ray emission can reveal the physical conditions of the interaction of the precessing jet of SS 433 with the material of the surrounding supernova remnant W50 .

Methods : In two pointings in September/October 2004 for 30 ks each the eastern jet of SS 433 was observed with XMM-Newton to study the outermost parts of the “ ear ” and the X-ray bright emission region about 35′ from SS 433 .

Results : The spectra consist of two components : a non-thermal power law with photon index \Gamma \sim 2.17 \pm 0.02 and a thermal component at a typical temperature of kT \sim 0.3 keV .
The X-ray emission seems to fill the whole interior region of the radio remnant W50 .
The jet terminates in the eastern “ ear ” in a ring-like terminal shock which indicates a flow with a kind of hollow-cone morphology .
The spatial coincidence of X-ray and radio emission suggests physical conditions similar to those found at the outer shocks of ordinary supernova remnants .
The bright emission region closer to SS 433 radiates non-thermally in a spatially well confined geometry at higher X-ray energies .
At soft X-rays the shape of the region gets blurred , centered on the hard lenticular emission .
The shape of this region and the bend in the jet propagation direction might be caused by the interaction of a re-collimated jet with the outer , non homogeneous interstellar matter distribution .

Conclusions : The physical conditions leading to the re-collimation of the jet and the peculiar emission morphology are far from being understood and require deeper observations as well as a detailed modeling of the interaction of a jet with its surroundings .