Digital Calorimeter R&D
(Digital) Calorimetry:
Calorimeters in particle physics are used to detect particles and measure their energy. This happens by absorbing the particle and in that process measure its energy. An example of such a calorimeter is the liquid argon calorimeter of the ATLAS experiment: Here, a particle is absorbed and converted within lead-steel absorbers to a shower of low-energetic particles. These low-energetic particles then create so-called scintillation light in the liquid argon which is interleaved with the absorbers. By measuring the “amount” (i.e. energy sum) of that light, one can deduce the energy of the incident particle.
We are working in collaboration with DESY Zeuthen and research groups in the UK on the development of digital calorimeters.
The fundamental difference of the digital readout to the analog mode described above is, that instead of measuring the energy of the scintillation light produced in the shower of the incident particle, one measures the number of particles produced in the shower. The number of particles is strongly correlated with the energy of the original particle. As the deposited energy in the detector can fluctuate due to the nature of using thin absorbers (so-called Landau fluctuations), it might be advantageous to not measure the energy itself but count particles and deduce their energy. This is what we are studying.
Our research: the DECAL sensor
In our current project we are investigating an depleted monolithic active pixel sensor (DMAPS) device called DECAL. The shower particles create electron-hole pairs in the 18 µm epitaxial silicon layer of the DECAL. These are collected and read out directly on the chip. The chip then sends the information of how many hits were recorded per measurement unit (so-called strips or pads) to the data-acquisition system.
Right: A technical sketch of the cross section of a DMAPS. Charge is created in the epitaxial layer by a traversing particle and collected in the collection electrode. The readout transistors are implemented in the same silicon bulk but are protected by (deep) p- and n-wells.
Our test systems
In 2022, we also bought a laser characterization system. This system will allow us to target single detector elements and therefore understand the sensor even better. Further, the laser will allow us to shine light both from the backside and the side into the sensor, giving us an additional handle to investigate it behavior.
Previous projects
The studies we have been performing in projects with current and former students:
- Tuning of the sensor to ensure that every element of the sensor behaves the same for data taking,
- Investigation on the impact of biasing the sensor (see bias voltage at pn-junction),
- Investigation of the impact and sources of cross-talk between different sensor elements (pixels),
These studies were accomplished also through the usage of radioactive sources and x-rays.
Potential projects for bachelor and master theses or internships
All projects require a basic programming knowledge. The readout software is written in C++ using CERN’s ROOT package. For all tasks, you will be required to manipulate the software and write new functions to perform the required studies. In the time scale of all projects we have allocated time for you to learn the necessary skills. For example, in a previous bachelor project, the student knew only basic Python programming and was able to learn the necessary skills to perform their bachelor’s project without issues.
Here you will find a list of potential projects. This list can be extended and further projects can be developed depending on the student’s skills and interests. If you are interested in working with us, please contact Dr. Hannsjörg Weber (weberhaa@hu-berlin.de), Prof. Cigdem Issever (isseverc@hu-berlin.de), or Prof. Steven Worm (steven.worm@hu-berlin.de).