Measurement of delta-rays in ATLAS silicon sensors

In the inner detector of the ATLAS experiment at the LHC, $\delta$-rays originating from particle interactions in the silicon sensors may cause additional hit channels. A method for identifying silicon hit clusters that are enlarged due to the emission of a $\delta$-ray is presented. Using pp collision data the expectation is confirmed that the $\delta$-ray production rate depends linearly on the path length of the particle in silicon, independently of layer radius and detector technology. The range of the $\delta$-rays, which is a property of the material and should not depend on anything else, is indeed found to be constant as a function of detector layer, path length in silicon and momentum of the particle traversing the silicon. As a by-product of this analysis a method is proposed that could correct for the effect of these $\delta$-rays, and this could be used to improve track reconstruction.