ESSnuSB

ESSnuSB
Name	ESSnuSB
Type	Particle physics experiment
Location	Lund, Sweden
Status	Proposed
Start	2015
Lead	European Spallation Source

ESSnuSB

ESSnuSB is a proposed long-baseline neutrino oscillation facility designed to exploit the European Spallation Source proton linac at Lund to produce an intense neutrino beam aimed at a far detector located in a deep underground laboratory. The project aims to measure CP violation in the leptonic sector by targeting the second oscillation maximum, complementing programs at T2K, NOvA, and future facilities such as DUNE and Hyper-Kamiokande. ESSnuSB connects accelerator development, neutrino detector technology, and geotechnical hosting in a multidisciplinary effort involving institutes across Europe and international partners.

Overview

ESSnuSB proposes to use the high-power pulsed proton beam from the European Spallation Source to generate a high-intensity, low-energy neutrino beam through pion decay, directing neutrinos toward a massive water-Cherenkov or liquid scintillator detector located at a baseline of several hundred kilometres. The concept builds on technologies tested at CERN, PSI, J-PARC, and Fermilab and seeks synergy with facilities like SNOLAB, Gran Sasso National Laboratory, Boulby Underground Laboratory, and the Canfranc Underground Laboratory. Key proponents include research groups from France, Italy, Spain, UK, Poland, Sweden, Germany, Norway, and collaborators from Japan, USA, and Canada.

Scientific Goals

The primary scientific goal is precision measurement of the leptonic CP violation phase by exploiting enhanced sensitivity at the second oscillation maximum for the atmospheric neutrino mass-squared splitting. ESSnuSB aims to determine the neutrino mass hierarchy and measure oscillation parameters including theta-23 octant and delta_CP with competitive resolution compared to DUNE and Hyper-Kamiokande. Secondary goals include searches for sterile neutrino signatures, precision cross-section measurements relevant to Super-Kamiokande analyses, contributions to proton decay limits, and detection prospects for core-collapse supernova neutrinos in coordination with SNEWS and other multimessenger observatories like IceCube and KM3NeT.

Accelerator and Beamline Design

The design centers on modifying the 5 MW, 2 GeV proton linac of the European Spallation Source to provide extra beam pulses for neutrino production without compromising spallation neutron operations. Proposed modifications borrow concepts from PSI high-power targets, the CERN SPS extraction systems, and J-PARC horn focusing technology. The neutrino production chain includes a graphite or beryllium target, magnetic horns inspired by NuMI and T2K designs, and a decay tunnel optimized for low-energy pion decay similar to concepts explored at ISIS and TRIUMF. Engineering challenges intersect with work at ITER and ESS civil works, requiring coordination with Vattenfall and regional infrastructure authorities.

Detector Concepts

Far detector concepts prioritize large-mass, cost-effective technologies with good neutrino energy reconstruction at sub-GeV energies. Water-Cherenkov solutions draw on experience from Super-Kamiokande, Hyper-Kamiokande, and INO proposals, employing ultra-pure water systems and large photomultiplier arrays akin to developments at KM3NeT and ANTARES. Liquid scintillator options leverage technology from Borexino, JUNO, and SNO+ to improve low-energy threshold and particle identification. Hybrid approaches consider segmented tracking calorimeters inspired by NOvA and MINERvA for near-detector suites, while magnetized spectrometers akin to OPERA and ICARUS could support flavor tagging and cross-section constraints.

Site and Infrastructure

Candidate far-site locations emphasize geological stability and existing underground facilities within several hundred kilometres of Lund, including studies near Garpenberg, Zinkgruvan, and potential revived interest in sites like Äspö Hard Rock Laboratory. Infrastructure planning involves tunnelling experience from projects such as Gotthard Base Tunnel and collaboration with national geological surveys like the Swedish Geological Survey and environmental assessments compliant with European Union regulations. Surface and near-site installations invoke precedents from CERN civil engineering, power distribution models of Vattenfall, and regional transport logistics linked to Malmö and Copenhagen.

Collaboration and Organization

The collaboration model follows multinational consortia similar to CERN experiments, DUNE consortium structures, and the governance of the European Spallation Source itself. Project management draws on frameworks used by ESFRI projects, with working groups spanning accelerator physics, detector R&D, software development referencing ROOT, and outreach informed by ICHEP and EPS community practices. Institutional partners include national laboratories and universities such as CERN, PSI, LPSC Grenoble, Università di Milano, University of Oxford, Uppsala University, Lund University, and research councils across Europe.

Timeline and Status

Since conceptual proposals in the 2010s, ESSnuSB has progressed through design studies, feasibility reports, and workshops at venues including CERN, Lund, and Stockholm. As of the mid-2020s the project remains at the proposed stage pending final site selection, funding commitments, and integration with the operational schedule of the European Spallation Source facility. Future milestones would align with decision points similar to those for DUNE and Hyper-Kamiokande and require coordination with national funding agencies, the European Commission, and international partners to move toward construction and commissioning phases.

Category:Neutrino experiments