Cover Story (Issue9, 2024) Measurement of solar pp neutrino flux using electron recoildata from PandaX-4T commissioning run

Author: Prof. Ben-Da Xu (Tsinghua University, Beijing)

The most abundantsolar neutrino from the proton-proton (pp) fusion provides us the uniqueprobe to the stellar core and is the only component that propagates to theearth through the vacuum oscillation mode. Though Borexino in 2012 managed topenetrate the C-14 beta decay curtain with clever tricks of energy spectrafitting, it is crucial to make precise and clean measurement of pp solar neutrino flux and energy spectrum. More than 20 years has passed since Professor Y. Suzuki, one of the main figures behind the solar neutrino measurement at Super-KamiokaNDE and the solution of the solar neutrino problem, proposed to use liquid xenon for real-time detection of elastic scattering of pp solar neutrino on electrons. The vision was a 10-ton liquid xenon that are freeof inevitably hindersome C-14 with organic liquid scintillators. Today, the vision is about to come true.

The PandaX collaboration utilized the PandaX-4T dual-phased liquid-xenon TPC to search for pp neutrinos. Although the electron-scattering signals are indistinguishable from the overwhelming beta and double-beta decays of Kr-85 and Xe-136, the collaboration managed to set a meaningful limit of 23.3×10¹⁰s^-1cm^-2 with a central value of 8×10¹⁰ s^-1cm^-2, consistent with the prediction of standard solar model. It marks the beginning of a new era to detect solar neutrino with direct dark-matter search experiments, with more excitement ahead of us when PandaX-4T finishes full

data-taking, afterthe upgrade of distillation tower to suppress Kr, or possibly deploying separate Xe-136 depleted and enriched liquid xenon sub-detectors optimized for solar neutrino and neutrinoless double-beta decay.

References

[1] Xiaoying Lu etal. (PandaX Collaboration), Chin. Phys. C 48, 091001 (2024), arXiv: 2401.07045[hep-ex]