Vertex detector for BELLE II
Radiation tolerance
Fig. 6: Optimization of the gate dielectric. shift
the ribbon tension after irradiation with a high dose.
One of the big challenges at Belle II is the high one radiation background. This comes from different sources such as the impact of electrons on atoms imperfect vacuum, but also from QED processes. The resulting occupation can in the first position of the detector reduced by the very fast readout damage to the detector due to radiation remains in the oxide and substrate. Mainly changes due to damage to the oxide, the threshold voltage of the DEPFETs and there is an increased dark current, which
caused by damage to the silicon. DEPFETs with ionizing radiation up to 10 Mrad irradiated show a negligible increase in noise, but a change in threshold voltage up to 25 V. Such changes are difficult to compensate for, v. a. in the case of non-uniform radiation. The solution is one optimization of the gate dielectric through a thin one silicon dioxide and an additional layer of silicon nitride suitable thickness. These measures can threshold voltage change after 10 Mrad to about 3 V. to press.
Fig. 7: Expected parameter for the spatial resolution of the
interaction point (in z) of Belle II compared to
Belle (PXD and SVD combined).
Physical benefits
The fundamental matter-antimatter asymmetry in the universe points to new CP violating effects beyond the standard model (cf. Nobel Prize 2008). These effects are characterized by high mass scales. Traces of new physics can be experimented with quantum entangled neutral B mesons are sought. These mesons will be produced in e + -e - accelerators. Belle II is through quantum loop processes are sensitive in the TeV area - at energies larger than accessible at the LHC. With the DEPFET based vertex detector the lane resolution of Belle II significant compared to Belle increased, with a hostile environment nearby of the interaction point.