Impact of reactor antineutrinos on the neutrino floor in low-mass WIMP-like dark matter searches

The sensitivity of conventional direct dark matter searches for weakly interacting massive particles (WIMPs) is ultimately limited by coherent elastic neutrino-nucleus scattering ( <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:mrow> <a:mi>CE</a:mi> <a:mi>ν</a:mi> <a:mi>NS</a:mi> </a:mrow> </a:math> ), which produces nuclear recoils indistinguishable from WIMP signals and defines the so-called . While the effects of solar neutrinos, geoneutrinos, diffuse supernova neutrinos, and atmospheric neutrinos have been extensively studied in this context, the contribution from reactor antineutrinos has received comparatively little attention. We present the first systematic evaluation of how reactor antineutrino fluxes, modeled as a function of reactor-detector distance, modify the neutrino floor for low-mass WIMP searches using SuperCDMS-like high-voltage germanium detectors. Both discovery-limit and opacity-based formulations of the neutrino floor are examined under consistent assumptions. We find that proximity to gigawatt-scale reactors within <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"> <c:mo>∼</c:mo> <c:mn>10</c:mn> <c:mtext> </c:mtext> <c:mtext> </c:mtext> <c:mi>km</c:mi> </c:math> can raise the neutrino floor by up to a few orders of magnitude, significantly reducing the sensitivity to sub- <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"> <e:mn>10</e:mn> <e:mtext> </e:mtext> <e:mtext> </e:mtext> <e:mi>GeV</e:mi> <e:mo>/</e:mo> <e:msup> <e:mi>c</e:mi> <e:mn>2</e:mn> </e:msup> </e:math> dark matter. <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"> <g:mrow> <g:mi>Beyond</g:mi> <g:mo stretchy="false">∼</g:mo> <g:mn>100</g:mn> <g:mtext> </g:mtext> <g:mtext> </g:mtext> <g:mi>km</g:mi> </g:mrow> </g:math> , the reactor contribution becomes negligible. These conclusions hold for both definitions of the neutrino floor and remain stable under reasonable variations in detector quenching, site-dependent geoneutrino flux, and reactor antineutrino flux uncertainties, emphasizing reactor proximity as a critical factor in site selection for future low-threshold dark matter experiments.