PROSPECT-II Physics Opportunities

Abstract

The Precision Reactor Oscillation and Spectrum Experiment, PROSPECT, has made world-leading measurements of reactor antineutrinos at short baselines. In its first phase, conducted at the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory, PROSPECT produced some of the strongest limits on eVscale sterile neutrinos, made a precision measurement of the reactor antineutrino spectrum from 235 U, and demonstrated the observation of reactor antineutrinos in an aboveground detector with good energy resolution and well-controlled backgrounds. The PROSPECT collaboration is now preparing an upgraded detector, PROSPECT-II, to probe yet unexplored parameter space for sterile neutrinos and contribute to a full resolution of the Reactor Antineutrino Anomaly, a longstanding puzzle in neutrino physics. By pressing forward on the world's most precise measurement of the 235 U antineutrino spectrum and measuring the absolute flux of antineutrinos from 235 U, PROSPECT-II will sharpen a tool with potential value for basic neutrino science, nuclear data validation, and nuclear security applications. Following a two-year deployment at HFIR, an additional PROSPECT-II deployment at a low enriched uranium reactor could make complementary measurements of the neutrino yield from other fission isotopes. PROSPECT-II provides a unique opportunity to continue the study of reactor antineutrinos at short baselines, taking advantage of demonstrated elements of the original PROSPECT design and close access to a highly enriched uranium reactor core.

Physics Opportunities with PROSPECT-II

“…In light of these recent developments, the physics opportunities for PROSPECT-II become even more tantalizing. In 2021, the PROSPECT collaboration published a detailed summary of the physics opportunities with an upgraded detector which can be rapidly deployed [6] Reactor experiments are highly complementary to accelerator-and source-based measurements and feature a flavor-pure, high-intensity source of ν e . While there have been questions about the uncertainties in absolute flux predictions, segmented detectors at short baselines are able to directly search for energy-dependent oscillation-induced spectral distortions that are the 'smoking-gun' of sterile neutrinos.…”

“…As described in Ref. [6], PROSPECT-II will produce a spectrum measurement that approaches or exceeds the precision of current prediction approaches, providing a stringent test of the underlying models and nuclear data. Furthermore, a joint analysis of spectrum measurements from Daya Bay and PROSPECT-II would produce purely data-driven reactor ν e spectrum models for future particle physics measurements and potential applications.…”

“…A flux precision of 2.5% is anticipated, with the dominant systematic being knowledge of the HFIR power (∼2%). When combined with flux measurements at LEU fueled reactors that have a more complex fuel mix, the pure 235 U ν e flux measurement performed by PROSPECT-II would improve the precision of IBD yields from all major fissioning isotopes [6].…”

“…The PROSPECT-II upgrade, which is described in detail in Ref. [6], resolves technical issues that abbreviated the first run, introduces design features that improve robustness and time-stability, and extends both the depth and the scope of the experiment's physics reach.…”

“…FIG.2. Sensitivity contours from one year (black, solid) and two years (pink, solid) of PROSPECT-II[6] data-taking compared to: Left: Already excluded parameter space from the relative reactor spectral experiments (gray, dashed), and the allowed region (blue, solid) from RAA (KI model),…”