"The new LZ dark matter search result is nearly five times better than the previous world’s best published result. "
Photo credits: © Matthew Kapust/Sanford Underground Research Facility
With the results presented this past August simultaneously at the TeV Particle Astrophysics 2024 and LIDINE 2024 conferences, the LUX-ZEPLIN (LZ) experiment has once again set a world-leading record in sensitivity to dark matter interactions.
Dark matter is one of the most important cosmological mysteries yet to be solved in physics. Several observations support the hypothesis that almost 85% of the matter content of the universe is a type of matter that does not interact with light or baryonic matter (aka regular matter), with its effects being felt only through gravitational interactions in galaxies and the largest cosmic structures. This hypothetical substance also binds our galaxy (and almost all other galaxies) together, wrapping the stars and interstellar dust of our Milky Way’s spiral arms tight in an all-encompassing blanket.
The LZ experiment aims to detect the faint signals of a dark matter interaction with regular matter. It contains at its core a time projection chamber (TPC) with 7 tonnes of ultra-pure liquid Xenon at -98ºC, observed by two arrays of 494 photomultiplier tubes capable of detecting individual photons, and surrounded by a reflector cage to maximize the detection of Xenon scintillation light. The TPC is enclosed within a multi-layer detector system built with the most radioactively clean materials available.
The new LZ dark matter search result is nearly five times better than the previous world’s best published result. For this analysis, the data from a year-long science campaign between May 2023 and May 2024 was combined with the first science data taken back in 2022. With a combined exposure of 4.2 tonne-years, LZ finds no evidence of WIMPs, the most favored dark matter candidate, above a mass of 9 GeV/c2. The new strongest upper limit on the spin-independent interaction cross section of WIMP dark matter with regular matter sits at 2.1×10−48 cm2 for a WIMP mass of 36 GeV/c2.
LIP has been a member of the LZ Collaboration since its inception. The researchers in the DarkMatter group at LIP are responsible for substantial contributions to the experiment, including studies of optical properties of materials used in the detector, software development for data analysis, detector monitoring and control, background modeling and searches for rare Xenon decays.
These latest results were published this week in an arXiv preprint [2410.17036]. A peer-reviewed publication will follow soon.
To mark Dark Matter Day on October 31, Paulo Brás, a researcher from LIP, has been invited by RÓMULO - Centro Ciência Viva at the University of Coimbra to present on the experimental side of dark matter searches. The event will take place in the Physics Department at the Faculty of Science and Technology of the University of Coimbra at 5:30 PM. This presentation, titled “Cosmic Ghostbusters,” will be followed by a talk from Violetta Sagun of CFisUC. Together, the talks will explore the mystery of dark matter as well as the ongoing efforts to detect it..