What’s the reason you want to do research in such a remote place like the BedrettoLab?

The physics laboratory we want to establish in the BedrettoLab is an extension of our own labs. One of the key challenges we face in particle physics is radioactivity coming from the atmosphere. You have to imagine that there is a constant rain of muons, particles that are part of cosmic radiation, permeating everything: our bodies, buildings, equipment. Muons can interact with materials and create background radiation through various secondary effects, such as spallation or neutron production. When you search for dark matter, the instruments you use are extremely sensitive to this kind of radiation. Therefore, you need to find places that shield you from it. That’s the main reason why much of our research and development happens in underground facilities, not just the experiments themselves, but also the building and testing of our instruments.
The BedrettoLab is perfect for this. It’s just a two hours journey from Zurich and therefore easily accessible. With around 1.5 km of granite above us, we’re shielded from most cosmic radiation. Plus, the lab is already well-equipped, which gives us a great starting point.

One of your major research topics is dark matter. Can you briefly explain what dark matter actually is?

What we know from astronomical and astrophysical observations is that there’s about five times more matter in the universe than we can actually see. That means most of the matter in the universe is invisible, we can’t see or touch it, but we know it’s there because of how its gravity affects stars and galaxies.
The behavior of dark matter suggests it should be a new kind of particle, but we haven’t directly detected it yet. And we don’t yet know its mass.
What we’re hoping to detect with our instruments is a collision between a dark matter particle and regular matter. Such a collision would produce a tiny flash of light and/or charge that our special detectors could measure.

Do you expect to detect such a collision once your equipment is set up in the BedrettoLab?

Detecting such a collision there is unlikely, simply because it would require very large particle detectors. What we plan to do in the BedrettoLab is to develop new techniques that we’ll later use in larger detectors and to perform measurements shielded from cosmic rays that helps us to improve our detectors. That said, our long-term vision for the BedrettoLab does include equipment that could, in principle, detect particles such as dark matter.

Can you explain your plans for developing fundamental physics research in the BedrettoLab?

We’ve already started our first measurements in the BedrettoLab to understand the environment there in terms of fundamental physics. This includes detecting radiation fields, electromagnetic interference, and vibrations. For the vibrations, we’re using data from the seismological instruments already in place.
The next step is to build a cleanroom in the cavern at tunnel meter 3,500. This cleanroom will open up several possibilities for experiments in fundamental physics. In the first phase, we’ll install a high-purity radiation counter to measure and screen materials for use in dark matter and neutrino detectors, perform precise isotope analysis, and that also can be used to examine the radioactive content of soil and water samples.
Later on, we’d like to add a dilution refrigerator. This device would allow us to detect potentially  dark matter even without large-scale equipment. It operates at temperatures close to absolute zero and is thus able to operate ultra-sensitive quantum sensors, which can detect tiny signals from rare particles.
A dilution refrigerator like this is rare in underground laboratories, so that would be quite special. Overall, I’m really impressed with the BedrettoLab and very optimistic about building a unique laboratory for fundamental physics there.

More info about Björn Penning's research at the BedrettoLab can be found here.

ETH Zurich has constructed a 120-meter-long side tunnel at the BedrettoLab, an underground research facility in Ticino (Switzerland). This new tunnel runs parallel to a carefully selected natural fault zone. Thanks to this specific location, researchers can study in detail how an earthquake starts at one point along a fault and then propagates until it runs out of energy. Using specialized equipment, an European research consortium is studying how faults move to better understand – and potentially predict – earthquakes. The project behind this initiative, called Fault Activation and Earthquake Rupture (FEAR), was funded by the European Research Council with €14 million. It aims to answer two of the most fundamental and unresolved questions in seismology: What happens just before an earthquake begins, and what causes it to stop. Researchers hope that answering these questions will help push the boundaries of earthquake predictability.

A unique on-fault observatory

To study earthquakes right at their source, the FEAR team drilled numerous boreholes. Most of them to monitor processes in the rock. Others to inject water and induce small earthquakes. They are equipped with a wide range of sensors and together form a novel on-fault monitoring network. The sensors are sensitive enough to detect earthquakes as small as magnitude -5 and will also measure other parameters such as fluid pressure in fractures, stress changes, and more. During the large-scale stimulation experiments the team is now preparing, hundreds of cubic meters of water are injected into the fault zone at high pressure. Fluid overpressure reduces the existing stress on fault planes, weakening them and making it easier for them to slip. This reduction in friction can trigger fault movement, resulting in induced earthquakes.

“An on-fault observatory is the missing piece of the puzzle in studying earthquakes”, says Prof. Domenico Giardini, one of the four principal investigators of the FEAR project. “We have excellent monitoring networks around the world. However, most are placed on the surface and are therefore located several kilometers away from the earthquake's point of origin. And even the few sensors placed in boreholes are usually only near fault zones, not directly within them.”

Triggering a magnitude 1 earthquake

In their upcoming experiments, the research team intends to induce a magnitude 1 earthquake. That is typically well below the threshold of human perception, which is around magnitude 2.5 at the surface. However, within meters of a fault, the resulting ground motions can be strong. The FEAR researchers build on extensive experience from the past 4 years, having conducted numerous injection experiments in the BedrettoLab, with increasing levels of injection pressure, and so far triggering earthquakes up to a magnitude of -0.5. The dense network of sensors, placed both on and around the target fault zone, will help the researchers understand what happens before, during, and after such an event. The researchers will also look for diagnostic precursory signals, which may not be detectable with less sensitive monitoring setups, and which could one day help predict large earthquakes. 

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