First beam test of UT sensors with the SALT 3.0 readout ASIC

This note presents the results of a beam test conducted at the Fermilab test beam facility in March 2019. The beam test represents the first such test of the UT readout ASIC, SALT 3.0, in a beam with production UT sensors. Two sensors were tested, one an unirradiated p-in-n sensor, and the second a n-in-p sensor irradiated to twice the maximum expected fluence. The beam test demonstrates that the SALT 3.0 ASIC meets our specifications, and can be used for the production. Due to specific issues with the data acquisition system that will not be present in the system in LHCb, a higher threshold was used in the beam test, corresponding to about 6$\sigma$ on the noise. With this higher threshold, the signal-to-noise ratio (S/N) and efficiency are measured. For the unirradiated sensor, a S/N of about 12 is achieved, with a single-hit efficiency of at least 99.5%. For the irradiated sensor, a S/N of about 11 is obtained, with a single-hit efficiency of about 94%. In the final system in LHCb with a proper threshold of about 3--4$\sigma$ of the noise, we expect to achieve a single-hit efficiency of at least 99.5%.