Cosmic ray physics with the ARGO-YBJ experiment

Abstract

The main scientific goals of the ARGO-YBJ ex- periment are -ray astronomy with a few hundreds GeV en- ergy threshold and cosmic ray physics below and around the knee of the primary energy spectrum (10 12 10 16 eV), where the transition from direct to indirect measurement techniques takes place. The ARGO-YBJ experiment, located at the Cos- mic Ray Observatory of Yangbajing (Tibet, P.R. of China, 4 300 m a.s.l.), is an unconventional Extensive Air Shower ar- ray of about 6,700 m 2 of active area, the only one exploiting the full-coverage technique at very high altitude currently in operation. The detector space-time granularity, performance and location offer a unique chance to make a detailed study of the structure of cosmic ray showers, in particular of the hadronic component. In this work we will focus on the main experimental results concerning cosmic ray and hadronic in- teraction physics: primary cosmic ray energy spectrum, an- tiproton over proton ratio, anisotropy in the cosmic ray flux and proton-air cross-section. Moreover, the possible data analysis improvements based on the use of all detailed infor- mation on the shower front (curvature, time width, rise time, ..), as well as the extension of the investigable energy range, allowed by the analog RPC readout, will be pointed out. nique at very high altitude presently in data taking. Location and detector features make ARGO-YBJ capable of investi- gating a wide range of fundamental issues in Cosmic Ray and Astroparticle Physics at relatively low energy threshold: - very high energy -ray astronomy, with an energy thresh- old of a few hundreds GeV; - search for emission of gamma ray bursts in the full GeV - TeV energy range; - study of cosmic rays (spectrum, composition, p/p ra- tio measurement, shower space-time structure, ...) starting at TeV energies; - Sun and heliosphere physics above Eth 1 GeV. In following sections, after a brief description of the detec- tor and its performance, the main results achieved on several items of cosmic ray physics will be presented and discussed.