Linear discriminant analysis of ultra-high energy cosmic ray composition: the importance of the detector resolution

P. HANSEN; J. ALVAREZ-MUÑIZ; R.A. VAZQUEZ; L.C. UZAL; P.M. GRANITTO

Malargüe, Mendoza

Encuentro; Auger Collaboration Meeting March 2014; 2014

Pierre Auger Observatory

We consider the case of a surface detector array with capabilities to measure the muonic component of the shower as well as the depth of the electromagnetic shower maximum Xmax with an almost 100% duty cycle. We address its potential to discriminate cosmic primaries on an event-by-event basis. In particular we study to which extent these new detector capabilities may help improving the separation of primary proton and iron-induced extensive air showers. We obtain the discrimination power when several composition-sensitive observables are (a) taken individually, and (b) combined in a linear discriminant analysis. The depth of shower maximum gives the best separation as an individual parameter as long as its measurement resolution is small (below ∼ 50 g/cm2), with a moderate improvement when other observables, such as the number of muons at ground, are combined in a linear discriminant analysis. However, if the measurement of Xmax degrades significantly, above about 50 g/cm2, measuring the number of muons with good accuracy and combining it with other observables, becomes crucial to achieve an event-by-event discrimination with large identification efficiency.