We describe the Belle II detector at the SuperKEKB electron–positron accelerator. SuperKEKB operates at the energy of the ϒ ( 4 S ) resonance where pairs of B mesons are produced in a coherent quantum mechanical state with no additional particles. Belle II, the first Super B factory detector, aims to achieve performance comparable to the original Belle and BaBar B factory experiments, which first measured the large CP violating effects in the B meson system, with much higher luminosity collisions and larger beam-induced backgrounds.

Detectors for extreme luminosity: Belle II

An upgrade of the existing Japanese flavor factory (KEKB in Tsukuba, Japan) is under construction, and foreseen for commissioning by the end of 2014. This new e+e− machine (“SuperKEKB”) will deliver an instantaneous luminosity of 8×1035 cm-2  s−1, which is 40 times higher than the world record set by KEKB. In order to be able to fully exploit the increased number of events and provide high precision measurements of the decay vertex of the B meson systems in such a harsh environment, the Belle detector will be upgraded (“Belle II”) and a new silicon vertex detector, based on the DEPFET technology, will be designed and constructed. The new pixel detector, close to the interaction point, will consist on two layers of DEPFET active pixel sensors. This technology combines the detection together with the in-pixel amplification by the integration, on every pixel, of a field effect transistor into a fully depleted silicon bulk. In Belle II, DEPFET sensors thinned down to 75 μ m with low power consumption and low intrinsic noise will be used.

The Belle II pixel detector: High precision with low material

We present a computer-farm based data reduction system for the pixel detector of the future Belle II experiment. Belle II is a major upgrade of the Belle detector that is currently ongoing in KEK (Tsukuba, Japan). Belle II will collect data from SuperKEKB, an asymmetric e+ e− collider whose target luminosity (8 × 1035 Hz/cm2) is a factor 40 larger than the present world record currently held by KEKB. The higher trigger rate (10 kHz) and worse background conditions (3% average occupancy on the pixel sensors) are a major challenge for both the detectors and the Data Acquisition System (DAQ) in particular for the inner part of the Belle II tracking system that consists of two cylindrical layers of DEPFET pixels sensors (PXD) placed just outside the beam pipe and very close to the Interaction Point (IP). The long integration times of the PXD together with the high background rate expected from pairs production occurring at the IP will lead to a large amount of data (more than 20 GB/s) that must be reduced by at least a factor 10 to satisfy the constraints coming from the available store space and bandwidth. A large amount of the background hits can be rejected by defining a set of Region Of Interest (ROI) on the PXD sensors and then recording just the data from the pixels inside the ROI. The ROIs are defined on an event by event basis by extrapolating back onto the PXD the charged tracks detected in the outer silicon tracker (a 4 layer double sided silicon strip detector) and reconstructed on line in real time. A demonstrator of this architecture was under beam test earlier this year in Desy (Hamburg, Germany). The demonstrator was operated on an electron beam whose momentum was in the 2 – 6 GeV/c range with a typical trigger rate of a few kHz in a magnetic field of strength up to 1 T. The demonstrator consists of one PXD sensor and 4 SVD sensors arranged in a 5 layers configuration mimicking the Belle II VXD. The detectors read out was a scaled down version of the Belle II DAQ + High Level Trigger (HLT) chain. The demonstrator was used to detect the particles, reconstruct in real time the trajectories, identify the ROI on the PXD plane and select the PXD hits belonging to it. In this contribution, we describe the requirements and the architecture of the final system together with the results obtained with the demonstrator.

/pdf/demonstrator-of-the-belle-ii-online-tracking-and-pixel-data-3tc8brpxf3.pdf

Demonstrator of the Belle II online tracking and pixel data reduction on the High Level Trigger system

New high-density interconnect hybrid circuits are under development for the CMS tracker modules at the HL-LHC. These hybrids will provide module connectivity between flip-chip front-end ASICs, strip sensors and a service board for the data transmission and powering. Rigid organic-based substrate prototypes and also a flexible hybrid design have been built, containing up to eight front-end flip chip ASICs. A description of the function of the hybrid circuit in the tracker, the first prototype designs, results of some electrical and mechanical properties from the prototypes, and examples of the integration of the hybrids into detector modules are presented.

https://iopscience.iop.org/article/10.1088/1748-0221/8/12/C12033/pdf

Hybrid circuit prototypes for the CMS Tracker upgrade front-end electronics

The Belle II Experiment at the High Energy Accelerator Research Organization (KEK) in Tsukuba, Japan, will explore the asymmetry between matter and antimatter and search for new physics beyond the standard model. 172 double-sided silicon strip detectors are arranged cylindrically in four layers around the collision point to be part of a system which measures the tracks of the collision products of electrons and positrons. A total of 1748 radiation-hard APV25 chips read out 128 silicon strips each and send the analog signals by time-division multiplexing out of the radiation zone to 48 Flash Analog Digital Converter Modules (FADC). Each of them applies processing to the data; for example, it uses a digital finite impulse response filter to compensate line signal distortions, and it extracts the peak timing and amplitude from a set of several data points for each hit, using a neural network. We present an overview of the SVD data readout system, along with front-end electronics, cabling, power supplies and data processing.

The Belle II SVD data readout system

The Belle II Silicon Vertex Detector

Belle II Silicon Vertex Detector

/pdf/belle-ii-silicon-vertex-detector-4zuhkkrwpr.pdf

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The Belle II Silicon Vertex Detector

Belle II Silicon Vertex Detector

Belle II Silicon Vertex Detector