Investigation of the mass sensitivity in the LOPES radio data

One of the main challenges in cosmic ray physics is a precise knowledge of the mass composition of ultra-high energy particles. The signature of the type of primary cosmic rays is explored here in the coherent radio emission from extensive air showers, detected in the MHz frequency range. A possible method to infer composition information from radio data is predicted by simulations (slope-method). It concerns the slope of the radio lateral distribution, which is strongly correlated with the depth of the shower maximum. The LOPES experiment, a digital interferometric antenna array, successfully detects radio events in the frequency band of 40-80 MHz and has the important advantage of taking data in coincidence with the particle detector array KASCADE-Grande. REAS3 is used to reproduce a set of LOPES detected events. The slope-method approach is applied to these simulated events and its applicability to the LOPES detected data is verified. Important parameters for Xmax reconstruction are derived. Thus Xmax values are obtained using radio-only information and compared with the expectations. A possible signature of mass composition in the LOPES data is discussed.