The Silicon Vertex Detector of Belle II
Veröffentlicht am 04.01.2012 in Proceedings of Science PoS(Vertex 2011) 022
The Belle experiment at KEK (Tsukuba, Japan) was successfully operated from 1999 until 2010 and confirmed the theoretical predictions of CP violation which led to the Nobel Prize in 2008. In order to precisely study rare decays, more statistics and thus a higher beam intensity are required. Consequently, a major upgrade of the KEKB machine is foreseen until 2014, aiming at a final luminosity of 8x10^35 cm^-2 s^-1, which is about 40 times higher than the previous peak value. This also implies changes to the Belle experiment and its innermost subdetector, the Silicon Vertex Detector (SVD) in particular. The SVD will be completely replaced, as it had already operated close to its limits in the past. All other subsystems will also be upgraded, leading to the new Belle II experiment.
The future SVD will consist of four layers of double-sided silicon strip detectors like the old one, but located at higher radii, as a new, two-layer DEPFET PiXel Detector (PXD) will be inserted around the beam pipe. Thus, the total sensitive area of the SVD will increase, and in order to mimimize the number of structural elements, it will be entirely composed of double-sided silicon detectors made from 6" wafers. The sensors will be read out by APV25 front-end chips that were originally developed for the CMS experiment at the LHC and that fulfill all the requirements of Belle II.
A large effort has been devoted to the minimization of the overall material budget. The so-called "Origami" chip-on-sensor concept was developed to obtain a good signal-to-noise ratio despite of the large sensors and fast shaping time, yet keeping the overall radiation length at a very low level thanks to light-weight composite materials for the mechanical structure and a highly efficient CO2 cooling scheme.
Multiple samples along the shaped waveform will be read out by the APV25 chip such that the peak of the shaping curve can be reconstructed with high precision, allowing to discard off-time background hits and thus reducing the overall occupancy significantly, which leads to better track matching efficiency.
Autoren: Thomas Bergauer, Markus Friedl, Christian Irmler, Manfred Valentan, Immanuel Gfall, Annekathrin Frankenberger, Paul Dolejschi, Thomas Obermayer, Dusko Smiljic
weitere Autoren: Yoshiyuki Onuki, Toru Tsuboyama
Kategorie: Reviewed Paper