Scientists show that LZ is the world’s most sensitive dark matter detector

_{English version: Diana Taborda}

The LUX-ZEPLIN (LZ) international collaboration experiment, which integrates a team of LIP-Coimbra (Laboratory of Instrumentation and Experimental Particle Physics | University of Coimbra) has just passed a check-out phase of startup operations and delivered first results. The LUX-ZEPLIN (LZ) experiment is an innovative and uniquely sensitive dark matter detector. In only 60 days of data collection, scientists were able to prove that it is actually the most sensitive dark matter experiment in the world.

Isabel Lopes, Principal Investigator of the LIP team participating in the experiment and professor at the Department of Physics of the Faculty of Sciences and Technology of the University of Coimbra claims that these results (available at https://lz.lbl.gov/ ) “are a crucial step in the detection of dark matter particles”

Dark matter particles are matter that does not emit, absorb, or scatter light. Dark matter particles have never actually been detected – but according to the scientists involved, that may be about to change. The countdown may have started with the results from LZ’s first 60 “live days” of testing. LZ spokesperson Hugh Lippincott of the University of California Santa Barbara said, “We plan to collect about 20 times more data in the coming years, so we’re only getting started. There’s a lot of science to do and it’s very exciting!”

Although unseen, dark matter’s presence and gravitational pull are nonetheless fundamental to our understanding of the universe. For example, the presence of dark matter, estimated to be about 85 percent of the total mass of the universe, shapes the form and movement of galaxies, and it is invoked by researchers to explain what is known about the large-scale structure and expansion of the universe.

The heart of the LZ dark matter detector is comprised of two nested titanium tanks filled with ten tonnes of very pure liquid xenon and viewed by two arrays of photomultiplier tubes (PMTs) able to detect faint sources of light. The titanium tanks reside in a larger detector system to catch particles that might mimic a dark matter signal.

Besides providing precise information about the position and type of particle interacting with its target, the LZ detector is also able to measure energy with great accuracy. « It is amazing how accurately it is possible to measure energy », says Guilherme Pereira, the PhD student who integrates the LZ LIP’s team, and was responsible for the studies that led to that high accuracy, further adding: “doing my PhD in this team has been an extremely challenging experience”

LZ is tucked away about a mile underground in an old gold mine changed into a laboratory (Sanford Lab). The experiment is underground to protect it from cosmic radiation at the surface that could drown out dark matter signals.

The international team involves 250 scientists and engineers from over 35 institutions from the US, UK, Portugal, and South Korea. The Portuguese team includes researchers, PhD and Master’s students at LIP, a founding member of the LZ collaboration.

The LIP team has provided numerous fundamental contribution to the LZ experiment, including “the development and implementation of the detector control system - the experiment's core system - and of the system that allows monitoring in real time the data acquired by the LZ. It has also developed key advanced tools for data analysis and processing and has led studies of rare xenon decays that are among the most rare events in the universe», adds Isabel Lopes.

The participation of LIP in the LZ experiment is supported by the Portuguese Foundation for Science and Technology (FCT). LZ is funded by the US Department of Energy (DOE), the Science & Technology Facilities Council of the United Kingdom, the Institute for Basic Science of South Korea and collaborating institutions