Sb for photon-hadron discrimination

GERMÁN ROS; G. A. MEDINA-TANCO; A.D. SUPANITSKY; LUIS DEL PERAL; MARÍA DOLORES RODRÍGUEZ-FRÍAS

Malargüe

Otro; Reunion de la Colaboración Internacional Pierre Auger; 2010

Colaboración Internacional Pierre Auger

The parameter S b was first suggested for proton-iron discrimination in [1] and more details are given in [2,3]. Among other analysis, it was shown that the best value for Sb exponent is b = 3.0 in case of hadron discrimination and that, under the same realistic experimental conditions, the composition could be more accurately determined from S3 than by using the risetime or Xmax. In this GAP, we apply Sb to discriminate between photons and hadrons. We expect Sb to discriminate better hadrons from photons than hadrons from themselves because Sb is very sensitive to the difference in the muon component. The definition has been optimized showing that it is better to use b = 4.0 to that end. We have compared the separation power of S 4 and the parameters most commonly used for photon searches, i.e. the risetime at 1000 meters from shower axis (t_1/2 (1000)), the radius of curvature (R) and the number of candidate stations (N_cand). S4 has a larger separation power, especially compared to the t_1/2(1000) and R that were used in the Auger paper about the photon limit with SD [4]. Therefore, using S4 we could not only improve the current photon limit, but also could allow us to extendit below 10^19 eV where t_1/2(1000) and R are not very useful. In addition, S4 does not depend on the zenith angle while the other parameters do, which could simplify the search for photon candidates.