XLZD

XLZD (XENON-LZ-DARWIN) is a next-generation observatory in astroparticle physics. As highlighted in the name, XLZD is formed by the XENON and LZ collaborations that currently have running detectors aimed primarly at WIMP direct detection (but with many other physics channels!), and by the DARWIN collaboration whose goal is to develop the required technology to build a ~50 tonne-scale dual-phase xenon time projection chamber (TPC). The members of these collaboration signed a Memorandum of Understanding in July 2021 and the new XLZD collaboration was officially formed in September 2024.

The primary goal of XLZD is to search for WIMP dark matter with spin-independent interaction cross-sections down to the irreducible background of neutrino interactions, the "neutrino fog". With a conservative 200 t·yr exposure it will reach 90% exclusion sensitivity down to a cross-section of 2×10⁻⁴⁹ cm² and 3σ evidence capability at a cross-section of 7×10⁻⁴⁹ cm², for a 40 GeV/c2 WIMP.

Neutrinos themselves are also an interesting physics chanel for XLZD. With a lower energy threshold than current neutrino experiments and its ultra low background level, XLZD will even be sensitive to low energy solar neutrinos (pp, ⁷Be), as well as to the neutrinoless double beta decay of ¹³⁶Xe, which has an abundance of 8.9 % in natural xenon. Other rare-event searches with DARWIN will include the coherent neutrino scattering of ⁸B and galactic supernova neutrinos and the observation of axions and axion-like-particles.
To achieve these goals, the collaboration is planning to build a ~3 m high and ~3 m wide dual-phase TPC filled with ~78 tonnes (~60 tonnes active) of liquid xenon (LXe). To detect the light produced by an interaction in LXe, two arrays of photosensors are placed one at the top and one at the bottom of the TPC. The arrays host a total of almost 2400 PMTs, 3-inch diameter, as planned in the baseline design.
More info on the XLZD detector and the science channels are in our Design Book (arXiv).

Sensitivity study for the neutrinoless double beta decay of ¹³⁶Xe show that XLZD will be competitive with dedicated experiments, with a 3σ discovery potential half-life of 5.7×10²⁷ yr (and a 90% CL exclusion of 1.3×10²⁸ yr) with 10 years of data taking, corresponding to a Majorana mass range of 7.3–31.3 meV (4.8–20.5 meV for the exclusion). You can find more info in the dedicated paper (arXiv).

Locally we work on different projects to develop the required technology and software tools needed for XLZD.

R&D

The main R&D project is Xenoscope, a facility with a 3 m high cryostat that is currently hosting a 2.6 m tall TPC (but with only ~15 cm diameter). Planned measurements include the drift of electrons and the light attenuation over the whole height. More on this in the Xenoscope page.

We also have a smaller cryogenic system called MarmotX. Once used to test the PMTs for the XENON1T and XENONnT experiments, it is now being upgraded to a TPC to test calibration source for XLZD and to merasure the  mean electronic excitation energy in liquid xenon, commonly known as the W-value. 
We also work on developing alternative photosensors to the one selected for the baseline design. We test 2-inch PMTs in MarmotX and SiPM (silicon photomultiplier) in LArS, a smaller facility that uses liquid argon and nitrogen. An array of SiPM is also installed in Xenoscope. More on these facilities in the Local experiments page. 

To select radiopure materials and to trace the amount of radioactivity in our detector, we need to screan all the components that are going to be used to build the XLZD detector. To do so we mantain and operate a high-purity germanium (HPGe) spectrometer, Gator, in a low-background environment underground at LNGS. More on this in the Gator page.

Simulations

Along with the R&D activities, the Monte Carlo (MC) simulations become crucial since they provide:

1. the requirements, in terms of background, to optimise the detector geometry and the materials in order to achieve the physics goals of the experiment.
2. the background reduction techniques, like adding extra shielding.
3. the science reach via the sensitivity studies.

Several members of our group actively worked in the Simulation Working Group of XENON and DARWIN, which have successfully developed a Geant4-based MC framework, and now on XLZD. This tool includes a detailed geometry of the detector as well as a post-processor that allows to model detector effects like the energy resolution. Among the achievements of the Simulation Group we find the identification of titanium as an excellent material for the cryostat and the cosmogenic activation of material in different undergorund laboratories. Among the sensitivity studies we worked on the neutrinoless double beta decay of ¹³⁶Xe. Future goals of the Simulation group are to reevaluate the sensitivity for WIMPs and the prospects for the observation of the coherent neutrino-nucleus scattering.