If dark matter interacts , even weakly , via non-gravitational forces , simulations predict that it will be preferentially scattered towards the trailing edge of the halo during collisions between galaxy clusters .
This will temporarily create a non-symmetric mass profile , with a trailing over-density along the direction of motion .
To test this hypothesis , we fit ( and subtract ) symmetric halos to the weak gravitational data of 72 merging galaxy clusters observed with the Hubble Space Telescope .
We convert the shear directly into excess \kappa and project in to a one dimensional profile .
We generate numerical simulations and find that the one dimensional profile is well described with simple Gaussian approximations .
We detect the weak lensing signal of trailing gas at a 4 \sigma confidence , finding a mean gas fraction of M _ { gas } / M _ { dm } = 0.13 \pm 0.035 .
We find no evidence for scattered dark matter particles with a estimated scattering fraction of f = 0.03 \pm 0.05 .
Finally we find that if we can reduce the statistical error on the positional estimate of a single dark matter halo to < 2.5 \arcsec , then we will be able to detect a scattering fraction of 10 \% at the 3 \sigma level with current surveys .
This potentially interesting new method can provide an important independent test for other complimentary studies of the self-interaction cross-section of dark matter .