[en] A silicon vertex detector has been developed for the BELLE experiment at the KEK B-factory to be used to determine the relative displacements of B-meson decay vertices for CP violation measurements. The device has been successfully installed and operated with high-luminosity beam conditions. The average strip yield is larger than 96%, including the preamplifier electronics yield and the detector is currently working stably with a signal-to-noise ratio of 17-40. The measured impact parameter resolution agrees with expectations based on Monte Carlo simulations, and the measured D⁰ lifetime is in good agreement with the particle data group's average of other measurements. Several B→J/ψK events produced at the Υ(4S) resonance have been detected and separate decay vertices have been found

[en] In many of the recent e⁺e^- particle physics experiments, monitoring of the accumulated dose in silicon is essential to maximize the lifetime of silicon vertex detectors operating in severe radiation environments. Using radiation-sensing field-effect transistors (RadFET) as radiation monitoring devices, we studied their responses during irradiation and during subsequent annealing. The relation between the RadFET response and the dose was determined by irradiations with a ⁶⁰Co source with known activity. The study of annealing at three different temperatures showed that RadFETs gradually anneal for up to 40%. Annealing can be fitted by a sum of two exponential functions with time constants of 3 and 85 days

[en] The Belle spectrometer was designed for studies of B meson decays at an asymmetric e⁺e^- collider operating at the Υ(4S) resonance. One of its crucial components, a silicon vertex detector (SVD), is placed just outside a cylindrical beryllium beam-pipe. After a year of Belle operation an upgraded version of SVD was installed during the regular summer shut-down. The new SVD follows the same design, with a few important improvements. Rad-soft readout electronics was replaced by rad-tolerant one, allowing for longer lifetime of the detector. A new radiation and temperature monitoring system was developed and implemented. A saw-shaped inner surface was introduced in the beam-pipe to prevent potential synchrotron radiation damage. The upgraded detector started operating successfully in October 2000

[en] Monolithic Active Pixel Sensors (MAPS) may become the building blocks of vertex detectors at future high luminosity e⁺e^- colliders. Requiring an active layer only a few tens of microns thick, MAPS can be thinned to ∼50μm, which reduces the multiple scattering of primary particles. Deep sub-micron CMOS processes allow for small pixel size, needed for adequate single point resolution and low occupancy at a Super B factory. Major concerns with MAPS are readout speed and signal stability for large pixel arrays. Laser bench test results of a full size prototype (CAP3) with 118,784 readout pixels and a 5-deep correlated double sampling pipeline are presented. Lessons learned are applied to a design iteration and investigation of two new digital readout sensor designs, all included in the CAP4 prototype chip

[en] Due to the need for precise vertexing at future higher luminosity B-factories with the expectedly increasing track densities and radiation exposures, upgrade of present silicon strip detectors with thin, radiation resistant pixel detectors is highly desired. Considerable progress in the technological development of thin CMOS based Monolithic Active Pixel Sensors (MAPS) in the last years makes them a realistic upgrade option and the feasibility studies of their application in Belle are actively pursued. The most serious concerns are their radiation hardness and their read-out speed. To address them, several prototypes denoted as Continuous Acquisition Pixel (CAP) sensors have been developed and tested. The latest of the CAP sensor prototypes is CAP3, designed in the TSMC 0.25μm process with a 5-deep sample pair pipeline in each pixel. A setup with several CAP3 sensors will be used to assess the performance of a full scale pixel read-out system running at realistic read-out speed. The results and plans for the next stages of R and D towards a full Pixel Vertex Detector (PVD) are presented

[en] Over the last few years great progress has been made in the technological development of Monolithic Active Pixel Sensors (MAPS) such that upgrades to existing vertex detectors using this technology are now actively being considered. Future vertex detection at an upgraded KEK-B factory, already the highest luminosity collider in the world, will require a detector technology capable of withstanding the increased track densities and larger radiation exposures. Near the beam pipe the current silicon strip detectors have projected occupancies in excess of 100%. Deep sub-micron MAPS look very promising to address this problem. In the context of an upgrade to the Belle vertex detector, the major obstacles to realizing such a device have been concerns about radiation hardness and readout speed. Two prototypes implemented in the TSMC 0.35 μm process have been developed to address these issues. Denoted the Continuous Acquisition Pixel, or CAP, the two variants of this architecture are distinguished in that CAP2 includes an 8-deep sampling pipeline within each 22.5 μm² pixel. Preliminary test results and remaining R and D issues are presented

[en] A future higher luminosity B-factory detector and concept study detectors for the proposed International Linear Collider require precision vertex reconstruction while coping with high track densities and radiation exposures. Compared with current silicon strip and hybrid pixels, a significant reduction in the overall detector material thickness is needed to achieve the desired vertex resolution. Considerable progress in the development of thin CMOS-based Monolithic Active Pixel Sensors (MAPS) in recent years makes them a viable technology option and feasibility studies are being actively pursued. The most serious concerns are their radiation hardness and their readout speed. To address these, several prototypes denoted as the Continuous Acquisition Pixel (CAP) sensors have been developed and tested. The latest of the CAP sensor prototypes is CAP3, designed in the TSMC 0.25μm process with a 5-deep Correlated Double Sample (CDS) pair pipeline in each pixel. A setup with several CAP3 sensors is under evaluation to assess the performance of a full-scale pixel readout system running at realistic readout speed. Given the similarity in the occupancy numbers and hit throughput requirements, per unit area, between a Belle vertex detector upgradation and the requirements for a future ILC pixel detector, this effort can be considered a small-scale functioning prototype for such a future system. The results and plans for the next stages of R and D towards a full Belle Pixel Vertex Detector (PVD) are presented

[en] We report measurements of charmonia produced in two-photon collisions and decaying to four-meson final states, where the meson is either a charged pion or a charged kaon. The analysis is based on a 395 fb^-1 data sample accumulated with the Belle detector at the KEKB electron-positron collider. We observe signals for the three C-even charmonia η_c(1S), χ_c0(1P) and χ_c2(1P) in the π⁺π^-π⁺π^-, K⁺K^-π⁺π^- and K⁺K^-K⁺K^- decay modes. No clear signals for η_c(2S) production are found in these decay modes. We have also studied resonant structures in charmonium decays to two-body intermediate meson resonances. We report the products of the two-photon decay width and the branching fractions, Γ_γγB, for each of the charmonium decay modes. (orig.)