CLOUD-II — Demonstrating SuperChooz & HORUS

The Double Chooz experiment delivered some of the most precise reactor-antineutrino measurements to date. With its legacy established and backgrounds well characterised, the Chooz underground site — powered by two N4-generation PWR cores — remains one of Europe’s most compelling facilities for reactor-antineutrino physics. Two new programmes, both built on the LiquidO detection paradigm — the deliberate use of opaque scintillating media for event-by-event topology imaging — are now charting the site’s third generation. The first is the CLOUD experiment, which inherits from the reactor-based, funded AntiMatterOTech programme (EIC Pathfinder) and is under construction in three experimental phases. Sited in the Ultra-Near-Detector position (~35 m from the reactor core), CLOUD will deploy LiquidO technology at the neutrino-physics scale for the first time, validating positron tagging and heavy-target loading capabilities unique to opaque scintillators. The expected rate of tens of thousands of antineutrinos per day enables a dedicated scientific programme alongside the technology demonstration, including sensitivity to spent-fuel antineutrinos relevant to nuclear safeguards. The second strand comprises SuperChooz (introduced in 2022) and HORUS (presented here for the first time). SuperChooz, located at Chooz and reusing the former Chooz-A power reactor cavern (1967–1991; first PWR in France), targets per-mille precision on θ₁₃ and, simultaneously, real-time solar-neutrino spectroscopy — including, for the first time, pp neutrinos via charged-current interactions on indium-loaded opaque scintillator, directly sensitive to vacuum θ₁₂. HORUS scales the solar channel to a dedicated observatory class, repurposing the former CEPSA/MOEVE refinery tank infrastructure in Tenerife (Canary Islands, Spain; 1930–2022). Both exploration programmes pioneer a sustainability-driven paradigm for large-scale scientific infrastructure, enabled by the intrinsic simplicity and industrial compatibility of the LiquidO detection technology. This talk presents the physics case, detector concepts, and the status of both the CLOUD demonstration programme — with an emphasis on CLOUD phase II — and, briefly, highlights the rationale for the prospective SuperChooz and HORUS.