Speaker
Dr
Paul Soler
(University of Glasgow)
Description
Hybrid Photon Detectors (HPD) have been chosen for the Ring Imaging
Cherenkov (RICH) detectors of the LHCb experiment. Photons impinging
on a multi-alkali S20 photo-cathode deposited on a quartz window
produce photo-electrons that are accelerated by a 20 kV potential
onto a silicon pixel sensor anode. The sensor is segmented into 8192
pixels of size 0.0625 mm x 0.5 mm that are electronically ORed
together into 1024 super-pixels of 0.5 mm x 0.5 mm. The cross-
focusing electron optics has a demagnification factor of five,
resulting in an effective pixel size of 2.5 mm x 2.5 mm at the photo-
cathode. The silicon sensor is bump-bonded to a pixel chip
fabricated using 0.25 m deep submicron radiation-tolerant
technology, which amplifies and digitizes the anode signals and
operates at the LHC speed of 40 MHz. The sensor/chip assembly is
mounted inside the HPD vacuum envelope.
Mass production of 484 HPDs for the LHCb experiment has commenced,
in close collaboration with industry. Measurements of HPD properties
carried out using dedicated laboratory test facilities will be
presented. These measurements will include supply currents,
threshold scans, maps of the pixel chip, the depletion voltage of
the silicon anode, the signal rate versus the applied high voltage,
the demagnification of the electron optics and the image distortions
due to magnetic fields. Stability studies under accelerated ageing
of quantum efficiency, dark count and ion feed-back rates are shown.
Finally, results from studies of the HPD performance in particle
test beams using Cherenkov light will be reported.
Primary author
Dr
Paul Soler
(University of Glasgow)
