The Belle silicon vertex detector: present performance and upgrade plans

The Belle detector has been operating at the KEKB colliding beam B-factory since 1999. It is a general purpose detector optimized to measure decay products of BB̄ pairs created at the Y(4S) resonance. The vertexing function provided by the Silicon Vertex Detector (SVD) is crucial for accurate B-decay measurements, particularly in searching for asymmetries in decay times of B̄ and B mesons, the essence of CP violation being studied at Belle. High radiation levels during early KEKB running soon rendered “SVD1.0” inoperable. It was replaced by another of the same design, built in parallel with the installation of SVD1.0. Improvement of the beam operating conditions allowed “SVD1.1” to provide vertex information for the first year of operation. During this time “SVD1.4” was built. This was mechanically identical, so needed no new tooling or structure development but used a radiation tolerant 0.8 μm process VA1′ chip and an upgraded detector design from Hamamatsu. SVD1.4 was installed in Belle during the 2000 summer shutdown and has successfully operated since. During this time, the KEKB luminosity has been raised to record values, above 4×1033 cm−2, whilst maintaining manageable radiation levels. A new SVD (SVD2) is under development to achieve enhanced radiation tolerance, to increase acceptance to that of the original Belle specification, and to introduce SVD information into the Belle level-1 trigger. This talk will give a status report of the Belle SVD, including performance achieved so far, and provide an overview of the SVD2 upgrade.