International Linear Collider
The International Linear Collider (ILC) is an accelerator project under discussion in Japan, where electrons and positrons will be accelerated to a center-of-mass energy between 250 GeV and 1 TeV in order to perform precision measurements of Z/W bosons, top quarks, and Higgs bosons. Our group is involved in one of the experiments and contributes to the development of a central tracking chamber. This detector, a time projection chamber (TPC), is an ideal tracking chamber due to its high efficiency, excellent energy resolution, and low material budget. Its properties can be further enhanced by using GridPix detectors for the signal readout.
Higgs physics at the ILC
The International Linear Collider (ILC) is a so-called "Higgs-factory" where collisions of electrons and positrons take place at an energy above the Higgs threshold. Because of the high event rate, both the production and decays of Higgs bosons can be studied in detail. In particular, rare processes such as the Higgs-Higgs self-coupling are important contributions to understand the Higgs mechanism in detail and to distinguish different models (Standard Model/SUSY). For this reason, particle physicists plan to build a linear accelerator up to 50 km long in Japan, which is ideally suited to this task. Here, precision measurements can be performed with polarized electrons and positrons at center-of-mass energies between 91 GeV and 1 TeV.
International Large Detector
A large particle detector consisting of several layer of sub-detectors will be erected around the interaction point. Two different detectors, the International Large Detector (ILD) and the Silicon Detector (SID) will be used in turns and exchanged by a push-pull principle on large air cushions. In the center of the ILD detector directly around the beamline there will be a vertex detector, which will use silicon pixel detectors to measure the exact point of origin of the particles. A large time projection chamber is planned as the central tracking detector, surrounded in the inside and on the outside by silicon stripe detectors. In addition, a high granularity electromagnetic and hadronic calorimeter are envisioned to measure the particle showers. These components are located in a magnetic field of B = 3.5 T, which is finally surrounded by muon detectors.
Time Projection Chamber
Our group is involved in the development of the Time Projection Chamber (TPC), which will detect and measure the tracks of long-lived particles. For this purpose, the LCTPC collaboration was founded, in which the development of a TPC with microstructured gas detectors is pursued. Besides the development of the field cage and the cathode, the focus is especially on the readout modules with the gas amplification stages, the readout pads and the electronics. Different approaches are being pursued here, such as Gas Electron Multipliers (GEMs), Micromegas or InGrids are being considered for gas amplification. The latter are part of GridPixe, which we are developing in our group as described in the Generic Detector Development section. Finally, the ions produced during the gas amplification are an important part of the studies, as they have to be neutralized as fast as possible. If they reach the drift volume, they lead to distortions of the electrostatic drift field due to their charges and thus to incorrectly reconstructed particle tracks.
GridPix readout
The use of GridPixes in a time projection chamber has several advantages: Due to the high number of track points and the low occupancy density, the particle tracks of interest can be found and reconstructed more easily and with higher reliability, even if there is an increased background. In addition, GridPix detectors provide spatial resolution independent of track direction, and the high resolution makes it possible to detect features in the track, such as secondary particle tracks (delta electrons) or kinks in the track, and to take them into account in the track reconstruction. However, approximately 50,000 to 60,000 GridPixes are required for the large chamber. To demonstrate the feasiblity of the interplay of many GridPixes, we have completed a setup with 160 GridPixes and operated it for two weeks in a test beam at DESY.
Now we focus on investigating the excellent properties of the GridPixes in more detail, such as the extremely high spatial and temporal resolution, the improved particle identification due to electron or cluster counting, and the ion backflow.
