The Status and Recent Results of the Telescope Array Experiment

The Telescope Array (TA) is a cosmic ray observatory of the largest aperture in the northern hemisphere, located in a desert in the western part of Utah, USA, to explore the origin of ultrahigh energy cosmic rays, photons, and neutrinos. The TA employs two types of detectors to observe air showers generated by cosmic rays in the atmosphere : the first is a “surface detector (SD)” of scintillation counters to measure shower particles on the ground, and the second is a “fluorescence detector (FD)” of telescopes installed in three stations to observe fluorescence light, caused by air shower particles, from the atmosphere above the SD array. The TA detectors have been in routine operation since May 2008. We measured the energy spectrum of cosmic rays with energy greater than 1018eV from our first 4-year data. We found a clear suppression of comic ray intensity above 5× 1019 eV. This feature is consistent with a theoretical prediction that cosmic rays lose energies due to interaction with cosmic microwave background photons during propagation in the intergalactic space. In this talk, We will present the status of the TA experiment and the recent results, including the energy spectrum, study of the primary mass composition, and searches for anisotropies in the arrival directions. We also briefly describe plans for further extensions.