First Indication of Solar $^8$B Neutrinos via Coherent Elastic Neutrino-Nucleus Scattering with XENONnT (2408.02877v2)

Abstract: We present the first measurement of nuclear recoils from solar $^8$B neutrinos via coherent elastic neutrino-nucleus scattering with the XENONnT dark matter experiment. The central detector of XENONnT is a low-background, two-phase time projection chamber with a 5.9 t sensitive liquid xenon target. A blind analysis with an exposure of 3.51 t$\times$yr resulted in 37 observed events above 0.5 keV, with ($26.4^{+1.4}_{-1.3}$) events expected from backgrounds. The background-only hypothesis is rejected with a statistical significance of 2.73 $\sigma$. The measured $^8$B solar neutrino flux of $(4.7_{-2.3}^{+3.6})\times 10^6 \mathrm{cm}^{-2}\mathrm{s}^{-1}$ is consistent with results from the Sudbury Neutrino Observatory. The measured neutrino flux-weighted CE$\nu$NS cross section on Xe of $(1.1^{+0.8}_{-0.5})\times10^{-39} \mathrm{cm}^2$ is consistent with the Standard Model prediction. This is the first direct measurement of nuclear recoils from solar neutrinos with a dark matter detector.

• The paper presents the first detection of solar 8B neutrinos via coherent elastic neutrino-nucleus scattering using the XENONnT detector.
• It employs a 5.9-ton liquid xenon time projection chamber and a blind analysis over a 3.51 t×yr exposure to isolate low-energy nuclear recoils.
• The experiment recorded 37 events above a 0.5 keV threshold, rejecting the background-only hypothesis with a significance of 2.73σ.

Overview of the First Indication of Solar $^8$B Neutrinos via Coherent Elastic Neutrino-Nucleus Scattering with XENONnT

The paper under review discusses the first measurement of nuclear recoils from solar $^8$B neutrinos through coherent elastic neutrino-nucleus scattering (CEvNS) using the XENONnT dark matter experiment. The investigation represents a significant milestone in neutrino physics, employing sophisticated detection technology to reveal interactions previously difficult to observe.

Experimental Design and Approach

The XENONnT experiment, situated at the INFN Laboratori Nazionali del Gran Sasso, is optimized to detect weakly interacting massive particles (WIMPs) using a two-phase time projection chamber (TPC) filled with 5.9 tons of liquid xenon (LXe). This setup is crucial for detecting low-energy nuclear recoils (NR) resulting from interactions with neutrinos. The researchers conducted a blind analysis over a 3.51 t×yr exposure, aiming to isolate $^8$B solar neutrinos, known for their potential to generate detectable signals via CEvNS.

The experimental apparatus involves multiple detection layers, including a muon veto, neutron veto, and the central LXe TPC. Each interaction in the TPC generates scintillation and ionization, detected as S1 and S2 signals. The observables S1 and S2 are further processed to pinpoint interaction locations and extract the recoil energy, enabling the measurement of NRs. Importantly, reducing the thresholds for S1 and S2 signals enhances sensitivity to the low-energy recoils anticipated from solar neutrinos.

Results and Interpretation

In the analysis, 37 events were observed above a 0.5 keV threshold, with an expected background of $26.4^{+1.4}_{-1.3}$ events. The background-only hypothesis was rejected at a 2.73σ significance level. Consequently, the measured $^8$B solar neutrino flux was $$(4.7_{-2.3}^{+3.6}) \times 10^6\, \mathrm{cm}^{-2}\mathrm{s}^{-1}$$, aligning with results from the Sudbury Neutrino Observatory. Furthermore, the calculated CEvNS cross section for Xe nuclei was found to be $(1.1^{+0.8}_{-0.5})\times10^{-39}\,\mathrm{cm}^2$, consistent with the predictions of the Standard Model (SM).

Significance and Future Directions

This research marks a pioneering use of a dark matter detector to measure nuclear recoils from solar neutrinos directly. The CEvNS interactions observed provide valuable confirmation of theoretical predictions, reinforcing our understanding of neutrino-Xe interactions and nuclear response. The experimental results hold promise for unraveling further aspects of particle physics and may contribute to dark matter research by providing critical benchmarks for future sensitivity goals.

The implications for both theoretical and practical fronts are substantial. The successful measurement pushes the frontiers of detector technology and highlights the interplay between neutrino and dark matter physics. As XENONnT continues operations, ongoing data collection will refine these measurements, potentially revealing new physics beyond the current SM framework.

Looking ahead, enhancements in detector sensitivity, reduced systematics, and increased exposure will pave the way for more precise measurements. These developments promise to augment our understanding of fundamental neutrino properties and their role in the universe, laying groundwork for future explorations in the field of astroparticle physics.