Speaker
Agnieszka Oblakowska-Mucha
(AGH University of Science and Technology (PL))
Description
The LHCb experiment is dedicated to searching for New Physics effects in the heavy flavour sector, precise measurements of CP violation and rare heavy meson decays. Precise tracking and vertexing around the interaction point is crucial in achieving these physics goals.
The LHCb VELO (VErtex LOcator) silicon micro-strip detector is the highest precision vertex detector at the LHC and is located at only 8 mm from the proton beams. Consequently the sensors receive a large and non uniform radiation dose.
The high spatial resolution (up to 4 microns single hit precision) is crucial for precise reconstruction of the primary and secondary vertices and in turn for achieving high quality measurements of the impact parameter and life time of beauty and charm mesons. The High Level Trigger relies heavily on these quantities.
The VELO comprises of 86 planar sensors fabricated from oxygenated n-on-n silicon (with one module made from p-on-n silicon) that operate in extremely harsh radiation environment (a dose of 0.5 x 1014 1MeV neutron equivalents /cm2 per fb-1 of data is predicted at the tip of the sensors). The radiation damage is monitored by three studies:
1) the currents drawn as a function of temperature and voltage,
2) studying the noise versus voltage behaviour,
3) charge collection efficiency, studied with tracks from proton-proton collisions, as a function of voltage.
Here we report the results from the first two studies, where signs of radiation damage being observed. Clear differences in behaviour, as expected, are observed between n-on-n and n-on-p sensors. Type inversion is observed in the tips of the n-on-n sensors.
The detector so far shows no significant performance degradation, however many interesting effects have been observed in the sensors.
The LHCb Silicon Tracker is constructed from silicon micro-strip detectors with long readout strips. It consists of one four-layer tracking station upstream of the LHCb spectrometer magnet and three stations downstream of the magnet. In this presentation, an overview of the first measurements of the observed radiation damage will also be shown.
Authors
Agnieszka Oblakowska-Mucha
(AGH University of Science and Technology (PL))
Tomasz Szumlak
(AGH University of Science and Technology (PL))
Co-authors
Chris Parkes
(University of Manchester (GB))
Mark Tobin
(Physik-Institut-Universitaet Zuerich)
Paula Collins
(CERN)
