美国科罗拉多矿业大学Joseph Smolsky等人近日取得一项新成果。他们报道了中微子波包空间范围的直接实验约束。该研究于2025年2月12日发表于国际一流学术期刊《自然》杂志上。

据了解，尽管中微子在宇宙中相对丰富，但它们是自然界中最不为人所知的基本粒子。事实上，在实验相关强度下发射的中微子的量子特性在理论上是有争议的，并且中微子波包的空间范围仅受到扩散为13个数量级的反应堆中微子振荡数据的松散约束。

研究组提出了一种方法，通过精确测量铍-7放射性衰变中释放的反冲子核的能量宽度，来直接获得这个量。衰变过程的最终状态包含一个反冲的锂-7核，它在产生时与一个电子中微子纠缠在一起。锂-7能谱是通过直接将铍-7放射性同位素，嵌入高分辨率超导隧道结（作为低温传感器操作）来高精度测量的。

在这种方法下，研究人员设定了6.2Pm，这意味着最终态系统的范围比原子核本身大一千多倍。从这个测量中，第一个，据他们所知，中微子波包的空间范围的直接下限被提取出来。这些结果可能会在几个领域产生影响，包括对中微子性质的理论理解，弱核衰变中的局域化性质以及中微子物理数据的解释。

附：英文原文

Title: Direct experimental constraints on the spatial extent of a neutrino wavepacket

Author: Smolsky, Joseph, Leach, Kyle G., Abells, Ryan, Amaro, Pedro, Andoche, Adrien, Borbridge, Keith, Bray, Connor, Cantor, Robin, Diercks, David, Fretwell, Spencer, Friedrich, Stephan, Gillespie, Abigail, Guerra, Mauro, Hall, Ad, Harris, Cameron N., Harris, Jackson T., Hayen, Leendert M., Hervieux, Paul-Antoine, Hinkle, Calvin, Kim, Geon-Bo, Kim, Inwook, Lamm, Amii, Lennarz, Annika, Lordi, Vincenzo, Machado, Jorge, Marino, Andrew, McKeen, David, Mougeot, Xavier, Ponce, Francisco, Ruiz, Chris, Samanta, Amit, Santos, Jos Paulo, Stone-Whitehead, Caitlyn, Taylor, John, Templet, Joseph, Upadhyayula, Sriteja, Wagner, Louis, Warburton, William K.

Issue&Volume: 2025-02-12

Abstract: Despite their high relative abundance in our Universe, neutrinos are the least understood fundamental particles of nature. In fact, the quantum properties of neutrinos emitted in experimentally relevant sources are theoretically contested1,2,3,4 and the spatial extent of the neutrino wavepacket is only loosely constrained by reactor neutrino oscillation data with a spread of 13 orders of magnitude5,6. Here we present a method to directly access this quantity by precisely measuring the energy width of the recoil daughter nucleus emitted in the radioactive decay of beryllium-7. The final state in the decay process contains a recoiling lithium-7 nucleus, which is entangled with an electron neutrino at creation. The lithium-7 energy spectrum is measured to high precision by directly embedding beryllium-7 radioisotopes into a high-resolution superconducting tunnel junction that is operated as a cryogenic sensor. Under this approach, we set a lower limit on the Heisenberg spatial uncertainty of the recoil daughter of 6.2pm, which implies that the final-state system is localized at a scale more than a thousand times larger than the nucleus itself. From this measurement, the first, to our knowledge, direct lower limit on the spatial extent of a neutrino wavepacket is extracted. These results may have implications in several areas including the theoretical understanding of neutrino properties, the nature of localization in weak nuclear decays and the interpretation of neutrino physics data.

DOI: 10.1038/s41586-024-08479-6

Source: https://www.nature.com/articles/s41586-024-08479-6