The Belle II Experiment

The Belle II detector is a general purpose spectrometer for the next-generation B-factory experiment at KEK. The Belle II efficiently collects data of e+-e− collisions made by the SuperKEKB accelerator. The Belle II consists of several sub-detector components:

  1. Two layers of pixelated silicon sensors (PXD) and four layers of double-sided silicon strip sensors (SVD) that measure decay vertex positions of B mesons and other particles,
  2. a central drift chamber (CDC) that measures trajectories, momenta and dE/dx information of charged particles,
  3. a barrel-shaped array of Time-Of-Propagation (TOP) counters that reconstruct, in spacial and time coordinates, the ring-image of Cherenkov light  cones emitted from charged particles passing through quartz radiator bars, another ring-imaging Cherenkov counters with aerogel radiator in the forward end-cap (A-RICH),
  4. an electromagnetic calorimeter (ECL) comprised of scintillator crystals located inside a superconducting solenoid coil that provides a 1.5 Tesla magnetic field, and
  5. an iron flux-return located outside of the coil which is instrumented to detect K0L mesons and to identify muons (KLM).

Our group contributes hardware and track fitting software.

Track Fitting with GENFIT

GENFIT is an experiment-independent framework for track reconstruction for particle and nuclear physics. It consists of three modular components: 

  • Track fitting algorithms: 
    Currently, GENFIT contains a Kalman Filter and a Deterministic Annealing Filter.
  • Track representations:
    These modules hold the data of track track parameters and can perform extrapolations of these parameters. GENFIT is distributed with two well-tested track representations. The RKTRackRep is used in the Belle II experiment.
  • Reconstruction hits:
    The hit dimensionality and the orientation of planar tracking detectors can be chosen freely. GENFIT is especially useful for tracking systems which include detectors which do not measure the passage of particles on predefined planes, like the CDC of Belle II. The concept of so-called virtual detector planes provides a simple mechanism to use these detector hits in a transparent way without any geometrical simplifications.

GENFIT has been developed in the framework of the PANDA experiment at FAIR, Darmstadt, Germany. It is also used in the Fopi, and GEM-TPC experiments. GENFIT is implemented in C++ and makes extensive use of object-oriented design. It is available at sourceforge under the LGPL v3. 

Read Out Electronics for the Silicon Pixel Detector

The silicon pixel detector, used in the Belle II experiment, is based on the Depleted P-Channel Field Effect Transistor (DEPFET) technology. This detector will be the innermost detector of the Belle II experiment and therefore will replace the two inner layers of the silicon vertex detector. The detector consists of two layers with 8 detector strips building the inner layer, and 12 strips building the outer layer of the pixel detector.

 

At our chair we develop a part of the read out electronics for the silicon pixel detector. The system that is called Data Handling Hybrid (DHH) is used to interface the read-out electronics of the DEPFET detector module to the data acquisition system of the Belle II experiment.

 

The main functions of the system are:

  1. Data read out and sub-event building:
    data from different detector modules is combined inside of the DHH system to a single sub-event that is sent for further processing downstream of the data read-out chain.
  2. Galvanic isolation of the DEPFET modules:
    Each DEPFET module can be calibrated to increase the performance of the detector with its own set of voltages. The DHH system used to simplify the electric interconnection between the DEPFET modules and the Data Acquisition System (DAQ) by decoupling voltage level using high speed optical links for communication with DAQ services.
  3. Distribution of the trigger and synchronization signals:
    The DHH system receives the trigger and synchronization information that is distributed serially in the experiment, and distributes it synchronous to the front-end electronics of the detector. Therefore the data that belongs to the same trigger is read out simultaneously.
  4. Control over the front-end electronics of the detector:
    Since the front-end electronics is connected only to the DHH system, the DHH system acts as a bridge between the front-end electronics and the DAQ software.
  5. Supervision of the read-out process.

The implementation of the DHH system is based on re-programmable data processors, FPGAs, which are widely used in commercial image processing systems.