The large particle accelerator LHC at CERN in Geneva enables scientists to get precious clues to understand the nature of matter in the next two decades of data taking. The power and performance of this huge research apparatus needs to be constantly improved for this task. A silicon sensor, which the junior researcher Claudia Merlassino is currently testing at the University of Bern, is planned to be used from 2025 in a large LHC experiment: ATLAS.
Claudia Merlassino is 26 years old. She is currently writing her PhD thesis in elementary particle physics at the University of Bern. Merlassino set up her experiment in a metal box in a lab room in the winding corridors of the Physics Institute. The Genova-born physicist unscrews the lid of the box. From inside, one hears a sucking sound coming from two plastic tubes. "I constantly spray the sensor I am testing in my experiment with dry air. This ensures that the sensor is not affected by moisture," says Claudia Merlassino.
Sensors in the heart of the ATLAS detector
The sensor, the young researcher probes in her box, covers a surface of a few square centimetres. It is the prototype of a sensor that will be used in the detector at CERN from 2025 onwards. Using this research equipment, CERN physicists study the elementary particles that emerge when protons collide in the particle accelerator LHC. The ATLAS detector is a huge apparatus that easily fills a triple gym. It is built in layers around the point where the protons collide in the LHC. Each of these layers are designed to detect particle tracks trying to identify their nature. Merlassino's sensor will be used in the fifth layer from the inside, just 25 cm in radial direction from the collision point. Thousands of these sensors will be incorporated into a cylindrical measuring instrument that will capture data from the very numerous proton-proton collisions.
Sensors must resist the huge particle radiation
"The sensor is in principle nothing else than a CMOS polycrystalline silicon sensor, as it is used today in every smartphone camera," says Merlassino. "It will help the ATLAS physicists in the future to capture elementary particles. During data taking the sensor will be exposed to an extremely high level of particle radiation, this can damage the crystal lattice of the silicon. I test how to make it resistant to particle radiation so that it will be possible to use it in the experiments over the years. " The Bernese scientist, who works under the direction of Prof. Antonio Ereditato and Prof. Michele Weber, is one of many researchers worldwide making the silicon sensor fit for future CERN experiments. Merlassino is examining four prototypes of sensors in her doctoral thesis. She repeatedly exposed the sensors to proton radiation in the cyclotron machine at Inselspital Bern - and subsequently examined the irradiated sensors in her box in the laboratory of the Physics Institute. She was allowed to use the cyclotron machine only once a week during the day, at night the facility is occupied for medical applications.
Career goal researcher
Claudia Merlassino wants to complete her doctoral thesis in 2019. Afterwards, the daughter of an Italian teacher and an administrative coworker wants to take up the profession that she has in her mind since she was 13: particle physics researcher. "Where I will end up at the moment is still in the stars. I would like to work somewhere in Europe so that I have the opportunity to visit my family in Milan on a regular basis. "
Author: Benedikt Vogel