Photodetectors and front-end electronics for the LHCb RICH upgrade

The RICH detectors of the LHCb experiment provide identification of hadrons produced in high energy protonproton collisions in the LHC at CERN over a wide momentum range (2-100 GeV/c). Cherenkov light is collected on photon detector planes sensitive to single photons. The RICH will be upgraded (in 2019) to read out every bunch crossing, at a rate of 40 MHz. The current hybrid photon detectors (HPD) will be replaced with multianode photomultiplier tubes (customisations of the Hamamatsu R11265 and the H12699 MaPMTs). These 8x8 pixel devices meet the experimental requirements thanks to their small pixel size, high gain, negligible dark count rate (similar to 50 Hz/cm(2)) and moderate cross-talk. The measured performance of several tubes is reported, together with their long-term stability. A new 8-channel front-end chip, named CLARO, has been designed in 0.35 mu m CMOS AMS technology for the MaPMT readout. The CLARO chip operates in binary mode and combines low power consumption (similar to 1 mW/Ch), wide bandwidth (baseline restored in <= 25ns) and radiation hardness. A 12-bit digital register permits the optimisation of the dynamic range and the threshold level for each channel and provides tools for the on-site calibration. The design choices and the characterization of the electronics are presented.