Stefan Schoppmann

Research

DarkMESA
since 2024	The parasitic electron beam-dump experiment DarkMESA at the MESA accelerator in Mainz has a powerful discovery potential for dark sector particles in the light mass range. The possible existence of such light dark matter (LDM) is a candidate explanation for the long-standing dark matter problem. With 10000 hours of operation time scheduled for P2 beam experiment at MESA, the dump of their 150 μA beam could act as a strong source of a LDM beam. LDM would be produced copiously in the relativistic electron-nucleus collisions taking place in the dump if it couples to electrons via vector mediators, called dark photons. After production, LDM particles could be detected within a shielded detector down-stream of the dump. A large advantage is provided by the boost at which particles are produced by the beam, allowing an improved reach at low masses. Moreover, such a search is unique since it can probe at the same time both the dark photon production and the LDM interaction. DarkMESA will benefit from the beam energy being below pion production threshold, producing very little beam-related backgrounds, and the very stable and continuous beam conditions necessary for the P2 experiment. Simulation studies show that DarkMESA is complementary to experiments at proton beam facilities. The studies indicate that DarkMESA has the potential to be sensitive to the LDM thermal relic targets, that are predicted by the annihilation cross sections for reproducing today's dark matter density. In the first phase, high-density Cherenkov radiators made from PbF₂ and SF5 lead glass are forseen as detector technology. For a later phase, opaque scintillation detectors with tracking capabilities are currently investigated. DarkMESA is going to have a final active volume of above 10 m³. Further information can be found at the collaboration website.
NuDoubt⁺⁺
since 2022	The NuDoubt⁺⁺ experiment aims at the measurement of two-neutrino and neutrinoless positive double weak decays (2β⁺/ECβ⁺). It is based on a new detector concept combining hybrid and opaque scintillators paired with a novel light read-out technique. The technology is particularly suitable detecting positrons (β⁺) signatures. In its first phase, NuDoubt⁺⁺ is going to operate under high-pressure loading of enriched Kr-78 gas. It expects to discover two-neutrino positive double weak decay modes of Kr-78 within 1 tonne-week exposure and is able to probe neutrinoless positive double weak decay modes at several orders of magnitude improved significance compared to current experimental limits. Later phases may involve searches for positive double weak decays in Xe-124 and Cd-106. Further information can be found at the collaboration website.
AM-OTech/CLOUD/LiquidO
since 2022	CLOUD is the first large scale project in the LiquidO detector family and, at the same time, it is the first ever tonne-scale opaque scintillation detector for neutrino physics. It will be deployed at the new Chooz ultra-near detector site located ~25 m from one of the Chooz nuclear reactors with overburden of less than 5 m. With more than 10,000 antineutrino interactions per day and an expected signal-to-background larger than 100, CLOUD is designed for unprecedented fundamental physics. The CLOUD-I phase addresses the fundamental physics programme associated with the primary goal of the AM-OTech innovation-based project that aims to develop non-intrusive industrial reactor monitoring. The subsequent CLOUD-II and CLOUD-III phases are independent scientific programmes exploring novel solar and geo-neutrino detection methodologies. Further information can be found at the collaboration websites of AM-OTech and CLOUD.
Eos
2021–2022	Eos seeks to perform a data-driven demonstration of event reconstruction using both Cherenkov and scintillation signals. The proposed Eos demonstrator is a few-ton scale detector, coupled with an array of fast PMTs and the ability to deploy a range of low-energy calibration sources. Eos will be constructed, calibrated and tested at LBNL. Results from Eos can influence the development of future large scale neutrino detectors. Further information can be found at the collaboration website.
Liquid Scintillator R&D
since 2017	In many neutrino experiments, the use of liquid scintillator as a detector material plays a decisive role. The loading of scintillator with metals allows a wide variety of usage cases. Special mixtures of different liquid scintillators allow precise adjustment of scintillator properties. However, despite their versatility, liquid scintillators also show disadvantages. A high load of non-scintillating additives, e.g. metal compounds, quickly leads to a low light yield, which makes the scintillator unusable. Likewise, even with unloaded scintillators, the absorption length limits the maximum size of detectors and the scintillation process leads to poor spatial and directional resolution. Two novel approaches allow to overcome these flaws: On the one hand, one can use a hybrid approach like the combination of water and scintillator or a slow scintillator to produce a detector material, which has the high light yield of scintillators and the good directional resolution of water-Cherenkov detectors. On the other hand, one can render the scintillator opaque and instrument it with localised light read-out, which allows better vertex resolution and, at the same time, higher loading. For further information, see the project websites on the opaque and water-based liquid scintillators.
Stereo
2016–2020	The Stereo Experiment is a neutrino oscillation experiment designed to search for the existence of sterile neutrinos. It is located at 10 m baseline from the high-flux research reactor at the ILL in Grenoble, France. With its segmented detector, Stereo is probing the most likely parameter space of the reactor antineutrino anomaly. It is also able to provide insides on the reactor spectral shape anomaly using a highly enriched uranium reactor. Further information can be found at the collaboration website.
T2K
2011–2014	T2K (Tokai to Kamioka) is a long-baseline neutrino experiment in Japan. It studies neutrino oscillations in a ~600 MeV beam of muon neutrinos produced by an accelerator at J-PARC. The near detector of T2K is located at a distance of 280 m from the beam target at J-PARC. As far detector T2K uses the Super-K detector, located 295 km off-axis from the beam source. T2K can measure the appearance of electron neutrinos as well as the disappearance of muon neutrinos. Moreover, neutrino and antineutrino beams can be produced. This allows precision measurements of leptonic oscillation parameters and CP-violation. Further information can be found at the collaboration website.
Double Chooz
2010–2020	Double Chooz searches for neutrino oscillations through the disapperance of electron anti-neutrinos. It uses two identical liquid scintillator detectors to measure the antineutrino flux of the Chooz-B nuclear reactors at a distance of 400 m and 1050 m. Its goal it the determination of the lepton mixing angle θ₁₃. In addition, Double Chooz provides information on the reactor spectral anomaly. Further information can be found at the collaboration website.