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Oxford LHCb and
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Denys Wilkinson Building Keble Road Oxford OX1 3RH |
LHCb Detector
LHCb RICH
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LHCb RICH System and Oxford Activities
This page contains an overview of the LHCb RICH system, of which Neville Harnew is Project Leader. Oxford's main interests in the RICH are in the areas of:
In addition, the group is active to formulating ideas about a RICH System for an Upgraded LHCb.
The mass of a particle can be determined from its momentum and speed. The momentum of a charged particle is measured by its deflection in a magnetic field. The purpose of the RICH detectors is to match up this information with a measurement of the particle's speed. A charged particle travelling faster than the local speed of light in a medium emits Cherenkov photons, at an angle which depends on the speed of the particle. A description of Cherenkov radiation. These photons are reflected by mirrors, out of the region where particles are travelling through the detector, to an array of photodetectors. This reduces the amount of material the particles travel through before reaching the last stages of the detector and protects the photodetectors from the large magnetic field and high radiation level. The photons produce a ring of hits on the photodectors, and the radius of this ring plus the reconstructed track is used to identify the type of particle. LHCb has chosen to use Hybrid Photon Detectors (HPDs).
This technology, developed at CERN, satisfies the LHCb requirements
of high sensitivity to single photons and fast readout speed. The
readout time has to be compatible with the |
Hybrid Photon Detectors (HPDs) combine in a single device vacuum photo-cathode technology with solid-state technology. A photoelectron is accelerated by an applied high voltage and focused onto the reverse biased silicon detector. The image is de-magnified by a factor of around 5 onto the 1024 pixels of the silicon detector, each 500 microns by 500 microns. For every photon 3000 to 5000 electron-hole pairs are created. The resulting signal is amplified by the front end readout chip, which is bump-bonded to the silicon. Fast signals (typical rise and fall times of a few ns) with
minimized time jitter ( |
A photo showing the three HPDs in the testbeam; on the right is the mirror. A successful testbeam was carried out in October 2004. An array of three HPDs was used to detect Cherenkov photons produced when charged particles travelled through an aerogel tile radiator. A paper describing this testbeam is in preparation. |
A screenshot from the LabVIEW data acquisition programme
