nEXO

nEXO
Name	nEXO
Caption	nEXO conceptual detector
Type	Neutrinoless double beta decay search
Location	SNOLAB, Sudbury Basin

nEXO

nEXO is a proposed next-generation neutrinoless double beta decay experiment centered on a large liquid xenon time projection chamber designed to probe the Majorana nature of the neutrino. The project builds on technologies and collaborations established by experiments such as EXO-200, KamLAND-Zen, GERDA, MAJORANA Demonstrator, and CUORE, and aims to achieve sensitivity competitive with plans like LEGEND and SNO+ while engaging institutions including SNOLAB, Lawrence Berkeley National Laboratory, Fermi National Accelerator Laboratory, SLAC National Accelerator Laboratory, and TRIUMF.

Overview

nEXO seeks to detect the rare process of neutrinoless double beta decay in the isotope ^136Xe by instrumenting several tonnes of isotopically enriched liquid xenon in a monolithic time projection chamber. The collaboration leverages experience from predecessors such as EXO-200 and KamLAND-Zen and coordinates with nuclear physics programs at Oak Ridge National Laboratory, Argonne National Laboratory, CERN, Institute for Nuclear Research (Russia), and academic groups at Massachusetts Institute of Technology, University of California, Berkeley, University of Michigan, Columbia University, and University of Oxford.

Scientific Goals

The primary scientific goal is to determine whether the neutrino is a Majorana fermion by observing neutrinoless double beta decay of ^136Xe, thereby testing mechanisms related to leptogenesis, seesaw mechanism, and extensions of the Standard Model (physics). nEXO aims to reach half-life sensitivities that probe the inverted ordering region suggested by global fits from groups such as Super-Kamiokande, SNO Collaboration, Daya Bay Reactor Neutrino Experiment, T2K, and NOvA. Secondary goals include measurements of two-neutrino double beta decay comparable to results from GERDA, CUORE-0, NEMO-3, and providing constraints relevant to cosmology results from Planck, WMAP, and BICEP2.

Detector Design

The detector concept centers on a cylindrical liquid xenon time projection chamber with segmented charge and scintillation readout, influenced by designs from EXO-200 and ideas developed at SLAC and Lawrence Berkeley National Laboratory. The cryostat and shielding plan includes ultra-clean materials sourcing from vendors used by MAJORANA Demonstrator and CUORE and deploys external water and cryogenic shields similar to setups at SNOLAB and Gran Sasso National Laboratory. Readout technologies under consideration include silicon photomultipliers from manufacturers that have worked with T2K and NOvA and low-radioactivity copper and cryogenic electronics akin to those used by GERDA and LEGEND.

Backgrounds and Sensitivity

Background reduction strategies draw on assay techniques used by EXO-200, MAJORANA Demonstrator, and CUORE, including material screening with low-background germanium detectors at facilities like Lawrence Berkeley National Laboratory and SNOLAB. Cosmogenic activation considerations reference studies at Gran Sasso National Laboratory and SURF, while external neutron and gamma backgrounds are modeled using inputs from SNO Collaboration, Borexino, and KamLAND. Sensitivity projections incorporate nuclear matrix element calculations from groups at University of Jyväskylä, Stony Brook University, University of Tübingen, and Los Alamos National Laboratory, and are compared with limits reported by GERDA Phase II, KamLAND-Zen 800, and CUORE.

Site and Infrastructure

nEXO plans baseline siting considerations at deep underground laboratories such as SNOLAB in the Sudbury Basin and evaluates alternatives including SURF at the Homestake Mine, and Gran Sasso National Laboratory in Italy. Infrastructure requirements reference cryogenic systems developed at Fermi National Accelerator Laboratory, low-background assay capabilities at SNOLAB and Pacific Northwest National Laboratory, and logistics frameworks used by EXO-200 and KamLAND-Zen for isotope transport and enrichment with partners like AVLIS providers and commercial enrichment facilities employed by CANDU fuel suppliers.

Collaboration and Management

The collaboration comprises an international consortium of universities, national laboratories, and institutes including Lawrence Berkeley National Laboratory, Fermilab, TRIUMF, SLAC, University of California, Berkeley, University of Chicago, University of British Columbia, McGill University, University of Tennessee, and Carnegie Mellon University. Management structures emulate practices from large physics projects such as ATLAS (experiment), CMS (experiment), DUNE (experiment), and IceCube Neutrino Observatory, with scientific advisory committees and review boards modeled after mechanisms at DOE-funded projects and NSF oversight in the United States and funding agencies like NSERC in Canada and CERN-partnered European agencies.

Timeline and Funding

The proposed timeline envisions R&D, prototyping, and technical design phases following precedents from EXO-200 and MAJORANA Demonstrator with construction targeting a multi-year schedule similar to LEGEND-1000 and nEXO-class projects, while funding pathways include national agency support from DOE (United States Department of Energy), NSERC, CERN contributions, and potential in-kind support from SNOLAB and partner laboratories. Cost and schedule estimates are benchmarked against large-scale experiments such as DUNE (experiment), LZ (experiment), and Hyper-Kamiokande, with staged reviews by agencies comparable to DOE Office of Science and international review panels.

Category:Particle physics experiments Category:Neutrino experiments