中微子是否是马约拉纳物资——确实，中微子是否是自身的反物资——仍然是物资物理学中最根本的未解之谜。世界各地的科学家正在地下深入寻找一种极其罕见的无中微子双β衰然而，要可靠地识别0νββ，首先必须准确测量标准模型允许的双中微子双β衰变过程（2νββ）的谱形和半衰期。
Recently, the PandaX Collaboration, using the ton-scale natural xenon PandaX-4T detector at the China Jinping Underground Laboratory, completed the most systematic and precise experimental study to date of the 2νββ spectrum of xenon-136, which also yields the world’s most precise half-life result for this isotope. The results were published on April 21, 2026, in the leading international physics journal Physical Review Letters.
https://journals.aps.org/prl/abstract/10.1103/v4c6-h6l6
Group photo of PandaX students and researchers in front of the detector
Xenon-136 is one of the most important candidate isotopes for 0νββ searches. Its natural abundance in xenon is about 8.9%. Experiments such as KamLAND-Zen and EXO-200/nEXO typically rely on costly isotopically enriched Xe-136. Once a detector reaches the ton scale, however, a natural xenon target with significant amount of Xe-136, can also enable high-precision measurements, offering a cost-effective and scalable alternative path. Leveraging its large target mass, low background level, and broad energy coverage, PandaX-4T measured the half-life of Xe-136 2νββ to be years, with a total relative uncertainty of 2.3%. This precision surpasses that of leading enriched-xenon experiments such as KamLAND-Zen and EXO-200, making it the most precise measurement worldwide to date. Beyond the half-life itself, this study also measures the relative size of higher-order contributions to the 2νββ nuclear matrix element and to search for double-beta decay modes accompanied by Majoron emission, setting the world’s most stringent constraint on the spectral-index model.