Аннотация
A new installation HORIZON-T is commissioned at the high altitude scientific station of P.N. Lebedev Institute at the Tien-Shan Mountains. The purpose of this installation is to study EAS arriving at the zenith angles close to the horizon. The installation consists of three Vavilov – Cherenkov detectors located at the center of the installation and five registration points for muons which are placed within 500 m from the center. With the help of HORIZON-T installation EAS events have been detected at zenith angles more than 65 degrees, some of which had muon pulses with the front being ahead of one from Vavilov – Cherenkov pulses by more than 20 ns. Simulations show that such EAS are most likely initiated by primary nuclei with the mass more than 10.