Layered water Cherenkov detector for the study of ultra high energy   cosmic rays
  We present a new design for the water Cherenkov detectors that are in use in various cosmic ray observatories. This novel design can provide a significant improvement in the independent measurement of the muonic and electromagnetic component of extensive air showers. From such multi-component data an event by event classification of the primary cosmic ray mass becomes possible. According to popular hadronic interaction models, such as EPOS-LHC or QGSJetII-04, the discriminating power between iron and hydrogen primaries reaches Fisher values of $\sim$ 2 or above for energies in excess of $10^{19}$ eV with a detector array layout similar to that of the Pierre Auger Observatory. 
Antoine Letessier-Selvon, Pierre Billoir, Miguel Blanco, Ioana C.   Maris, Mariangela Settimo
astro-ph.IM