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Merging clusters of galaxies are unique in their power to directly probe andplace limits on the self-interaction cross-section of dark matter. Detailedobservations of several merging clusters have shown the intracluster gas to bedisplaced from the centroids of dark matter and galaxy density by ram pressure,while the latter components are spatially coincident, consistent withcollisionless dark matter. This has been used to place upper limits on the darkmatter particle self-inteaction cross-section of order 1 cm^2/g. The clusterAbell 520 has been seen as a possible exception. We revisit A520 presenting newHST ACS mosaic images and a Magellan image set. We perform a detailed weaklensing analysis and show that the weak lensing mass measurements andmorphologies of the core galaxy-filled structures are mostly in good agreementwith previous works. There is however one significant difference -- we do notdetect the previously claimed "dark core" that contains excess mass with nosignificant galaxy overdensity at the location of the X-ray plasma. This peakhas been suggested to be indicative of a large self-interaction cross-sectionfor dark matter (at least ~5 sigma larger than the upper limit of 0.7 cm^2/gdetermined by observations of the Bullet Cluster). We find no such indicationand instead find that the mass distribution of A520, after subtraction of theX-ray plasma mass, is in good agreement with the luminosity distribution of thecluster galaxies. We conclude that A520 shows no evidence to contradict thecollisionless dark matter scenario.

On Dark Peaks and Missing Mass: A Weak Lensing Mass Reconstruction of the Merging Cluster System Abell 520