In this paper we report on the timing resolution obtained in a beam test with pions of 180 GeV/c momentum at CERN for the first production of 45 µm thick Ultra-Fast Silicon Detectors (UFSD). UFSD are based on the Low-Gain Avalanche Detector (LGAD) design, employing n-on-p silicon sensors with internal charge multiplication due to the presence of a thin, low-resistivity diffusion layer below the junction. The UFSD used in this test had a pad area of 1.7 mm 2 . The gain was measured to vary between 5 and 70 depending on the sensor bias voltage. The experimental setup included three UFSD and a fast trigger consisting of a quartz bar readout by a SiPM. The timing resolution was determined by doing Gaussian fits to the time-of-flight of the particles between one or more UFSD and the trigger counter. For a single UFSD the resolution was measured to be 34 ps for a bias voltage of 200 V, and 27 ps for a bias voltage of 230 V. For the combination of 3 UFSD the timing resolution was 20 ps for a bias voltage of 200 V, and 16 ps for a bias voltage of 230 V.In this paper we report on the timing resolution of the first production of 50 micro-meter thick Ultra-Fast Silicon Detectors (UFSD) as obtained in a beam test with pions of 180 GeV/c momentum. UFSD are based on the Low-Gain Avalanche Detectors (LGAD) design, employing n-on-p silicon sensors with internal charge multiplication due to the presence of a thin, low-resistivity diffusion layer below the junction. The UFSD used in this test belongs to the first production of thin (50 {\mu}m) sensors, with an pad area of 1.4 mm2. The gain was measured to vary between 5 and 70 depending on the bias voltage. The experimental setup included three UFSD and a fast trigger consisting of a quartz bar readout by a SiPM. The timing resolution, determined comparing the time of arrival of the particle in one or more UFSD and the trigger counter, for single UFSD was measured to be 35 ps for a bias voltage of 200 V, and 26 ps for a bias voltage of 240 V, and for the combination of 3 UFSD to be 20 ps for a bias voltage of 200 V, and 15 ps for a bias voltage of 240 V

Novel silicon detectors with charge gain were designed (Low Gain Avalanche Detectors - LGAD) to be used in particle physics experiments, medical and timing applications. They are based on a n++-p+-p structure where appropriate doping of multiplication layer (p^+) is needed to achieve high fields and impact ionization. Several wafers were processed with different junction parameters resulting in gains of up to 16 at high voltages. In order to study radiation hardness of LGAD, which is one of key requirements for future high energy experiments, several sets of diodes were irradiated with reactor neutrons, 192 MeV pions and 800 MeV protons to the equivalent fluences of up to Φeq=1016 cm−2. Transient Current Technique and charge collection measurements with LHC speed electronics were employed to characterize the detectors. It was found that the gain decreases with irradiation, which was attributed to effective acceptor removal in the multiplication layer. Other important aspects of operation of irradiated detectors such as leakage current and noise in the presence of charge multiplication were also investigated.