A new technique to measure cosmic ray energy and composition via (2+1)d lateral distribution function fits to surface detector array data

The concept of a one-dimensional lateral distribution function is extended to a set of (2+1)d functions which describe the spatial and temporal distributions of the muonic and electromagnetic components of extended air showers. By design, these functions incorporate the curvature and time structure of the shower front as well as the asymmetries in particle density and in time structure expected in inclined showers. These observables are sensitive to the mass of the primary cosmic ray and to the details of the hadronic interactions inducing the air shower. The (2+1)d functions smoothly interpolate between the values of X{sub max} and muon flux predicted by various simulations performed with different assumptions of primary composition and interaction model. A maximum likelihood fit to surface detector array data can then give simultaneous event-by-event measurements of the shower energy, X{sub max}, and the muon content, from which the primary composition may subsequently be inferred. The methods outlined are applicable to a large number of existing and future shower detector arrays covering a range of energies.