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Frank Simon | MPI for Physics | Germany

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Pixels in Spain

My Spanish weeks continue: After vacations in Tenerife, where I just returned very early Monday morning, I flew to Barcelona last night, and now I’m sitting in the first session of the DEPFET workshop, which focuses on the development of silicon pixel detectors based on the DEPFET principle.

Schematic of a single pixel in a DEPFET detector: The internal gate collects the charge deposited by a throughgoing particle. This in turn modulates the current when the pixel is read out, and gives information on the collected charge.

Schematic of a single pixel in a DEPFET detector: The internal gate collects the charge deposited by a throughgoing particle. This in turn modulates the current when the pixel is read out, and gives information on the collected charge.

A pixel in a DEPFET sensor is essentially a small transistor, where the gate of the transistor sees the charge that a passing particle deposits in the pixel. The obvious advantage of this technology is the built-in amplification, just as with a regular transistor. This allows the construction of very thin detectors, where particles only create a tiny amount of charge. This in turn is good for the precise measurement of particle tracks, since the material of the detectors themselves disturbs the particles and limits the accuracy, through an effect that we particle physicists call multiple scattering. Multiple scattering, small angle scattering reactions of the through-going charged particles in the electric field of the atoms of the detector material, gets worse for low-momentum particles. Thus, thin detectors are particularly important for lower energies. That is one of the reasons why the DEPFET technology was chosen for the new pixel vertex tracker of the Belle-II experiment.

We are currently discussing how to choose the right layout of the detector to achieve the best possible physics resolution of the detector. For this, detailed simulations of different detector geometries are performed.

While the DEPFET community is now very much focused on Belle-II, and thus on a new low-energy electron-positron collider, it is clear that we also have the International Linear Collider as the long term goal for our development in mind.

So, I’m looking forward to two interesting and hopefully productive days here in Barcelona.

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