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实验结果证实了异常,可以指向新的基本粒子 精选

已有 5651 次阅读 2022-6-18 15:59 |个人分类:新观察|系统分类:海外观察

实验结果证实了异常,可以指向新的基本粒子

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experiment-results-con.jpg

Fig. 1 Located deep underground at the Baksan Neutrino Observatory in the Caucasus mountains in Russia, the completed two-zone gallium target, at left, contains an inner and outer tank of gallium, which is irradiated by an electron neutrino source. Credit: A. A. Shikhin

experiment-results-con-1.jpg

Fig. 2 A set of 26 irradiated disks of chromium 51 are the source of electron neutrinos that react with gallium and produce germanium 71 at rates which can be measured against predicted rates. Credit: A. A. Shikhin

据美国洛斯·阿拉莫斯国家实验室 Los Alamos National Laboratory2022616日提供的消息,实验结果证实了异常,可以指向新的基本粒子(Experiment results confirm anomaly, could point to new elementary particle)。

新的科学结果证实了在以前的实验中看到的异常现象,这可能指向一种尚未被证实的新基本粒子,惰性中微子(sterile neutrino),或者表明需要对标准物理模型的一个方面进行新的解释,比如60年前首次测量到的中微子截面(neutrino cross section)。

洛斯·阿拉莫斯国家实验室是美国巴克桑惰性转化实验(Baksan Experiment on Sterile Transitions简称BEST)的主要合作机构,该实验的结果于202269日分别在《物理评论快报》(Physical Review Letters)和《物理评论C》( Physical Review C)杂志网站发表。详见:

 V. V. Barinov, B. T. Cleveland, S. N. Danshin, H. Ejiri, S. R. Elliott, D. Frekers, V. N. Gavrin, V. V. Gorbachev, D. S. Gorbunov, W. C. Haxton, T. V. Ibragimova, I. Kim, Yu. P. Kozlova, L. V. Kravchuk, V. V. Kuzminov, B. K. Lubsandorzhiev, Yu. M. Malyshkin, R. Massarczyk, V. A.  Matveev, I. N. Mirmov, J. S. Nico, A. L. Petelin, R. G. H. Robertson, D. Sinclair,A. A. Shikhin, V. A. Tarasov, G. V. Trubnikov, E. P. Veretenkin, J. F. Wilkerson, A. I. Zvir. Results from the Baksan Experiment on Sterile Transitions (BEST). Physical Review Letters, 2022, 128(23): 232501. DOI: 10.1103/PhysRevLett.128.232501. Published 9 June 2022. https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.128.232501

V. V. Barinov, S. N. Danshin, V. N. Gavrin, V. V. Gorbachev, D. S. Gorbunov, T. V. Ibragimova, Yu. P. Kozlova, L. V. Kravchuk, V. V. Kuzminov, B. K. Lubsandorzhiev, Yu. M. Malyshkin, I. N. Mirmov, A. A. Shikhin, E. P. Veretenkin, B. T. Cleveland, H. Ejiri, S. R. Elliott, I. Kim, R. Massarczyk, D. Frekers, W. C. Haxton, V. A. Matveev, G. V. Trubnikov, J. S. Nico, A. L. Petelin, V. A. Tarasov, A. I. Zvir, R. G. H. Robertson, D. Sinclair, J. F. Wilkerson. Search for electron-neutrino transitions to sterile states in the BEST experiment, Physical Review C, 2022, 105(6): 035502. DOI: 10.1103/PhysRevC.105.065502. Published 9 June 2022. https://journals.aps.org/prc/abstract/10.1103/PhysRevC.105.065502

评估数据团队的首席分析师、洛斯阿拉莫斯物理部门的成员史蒂夫·埃利奥特(Steve Elliott):“结果非常令人兴奋。这肯定重申了我们在之前的实验中看到的异常现象。但这意味着什么并不明显。现在关于惰性中微子的研究结果相互矛盾。如果结果表明基本的核物理或原子物理被误解了,那也会非常有趣。”洛斯阿拉莫斯团队的其他成员包括Ralph MassarczykInwook Kim

在俄罗斯高加索山脉的巴克桑中微子天文台(Baksan Neutrino Observatory in Russia's Caucasus Mountains)地下一英里多的地方,BEST使用了26个被辐照过的铬51(51Cr)圆盘,铬51是铬的一种合成放射性同位素,是3.4兆居里(3.4 megacurie)的电子中微子源,来辐照一个装有镓(gallium, Ga)的内外储罐。镓是一种柔软的银色金属,在以前的实验中也使用过,不过以前是在一个储罐中。来自铬51和镓的电子中微子之间的反应产生同位素锗71(71Ge)。实测结果表明,锗71的产率比理论模型预测的低20%-24%。这种差异与之前的实验中看到的异常现象一致。

BEST建立在一个太阳中微子实验(solar neutrino experiment)——苏美镓实验(Soviet-American Gallium Experiment 简称SAGE)的基础上,在这个实验中,洛斯阿拉莫斯国家实验室是20世纪80年代末开始的一个主要贡献者。该实验还使用了镓和高强度中微子源。那个实验和其他实验的结果表明电子中微子的缺失预测和实际结果之间的差异被称为"镓异常(gallium anomaly"。对这一缺陷的解释可以作为电子中微子和惰性中微子之间振荡的证据。

同样的异常现象在BEST实验中再次出现。可能的解释同样包括振荡成惰性中微子。这种假想的粒子可能构成了暗物质(dark matter)的重要组成部分,而暗物质是一种被认为构成物质宇宙绝大部分的前瞻性物质形式。然而,这种解释可能需要进一步的测试,因为每个储罐的测量结果大致相同,尽管低于预期。

对这一异常现象的其他解释包括,实验的理论输入可能存在误解,即物理本身需要重新研究。史蒂夫·埃利奥特指出,在这些能量下,电子中微子的横截面从未被测量过。例如,一个难以确认的测量截面的理论输入是原子核处的电子密度。

该实验的方法被彻底审查,以确保在研究方面准确无误,如辐射源放置或计数系统操作。未来的实验迭代,如果进行,可能包括一个不同的辐射源,具有更高的能量,更长的半衰期和更短的振荡波长的灵敏度。

上述介绍,仅供参考欲了解更多信息,敬请注意浏览原文或者相关报道

Results from the NEOS experiment on sterile neutrinos differ partly from the theoretical expectations 

AbstractDOI: 10.1103/PhysRevLett.128.232501

The Baksan Experiment on Sterile Transitions (BEST) was designed to investigate the deficit of electron neutrinos νe observed in previous gallium-based radiochemical measurements with high-intensity neutrino sources, commonly referred to as the “gallium anomaly,” which could be interpreted as evidence for oscillations between νe and sterile neutrino (νs) states. A 3.414-MCi 51Cr νe source was placed at the center of two nested Ga volumes and measurements were made of the production of 71Ge through the charged current reaction, 71Ga(νe, e)71Ge, at two average distances. The measured production rates for the inner and the outer targets, respectively, are [image.png(stat)±1.4(syst)] and [image.png(stat)±1.4(syst)] atoms of 71Ge/d. The ratio (R) of the measured rate of 71Ge production at each distance to the expected rate from the known cross section and experimental efficiencies are Rin=0.79±0.05 and Rout=0.77±0.05. The ratio of the outer to the inner result is 0.97±0.07, which is consistent with unity within uncertainty. The rates at each distance were found to be similar, but 20%–24% lower than expected, thus reaffirming the anomaly. These results are consistent with νeνs oscillations with a relatively large Δm2 (>0.5  eV2) and mixing sin22θ (≈0.4).

AbstractDOI: 10.1103/PhysRevC.105.065502

The Baksan Experiment on Sterile Transitions (BEST) probes the gallium anomaly and its possible connections to oscillations between active and sterile neutrinos. Based on the Gallium-Germanium Neutrino Telescope (GGNT) technology of the SAGE experiment, BEST employs two zones of liquid Ga target to explore neutrino oscillations on the meter scale. Oscillations on this short scale could produce deficits in the 71Ge production rates within the two zones, as well as a possible rate difference between the zones. From July 5th to October 13th 2019, the two-zone target was exposed to a primarily monoenergetic, 3.4-MCi 51Cr neutrino source 10 times for a total of 20 independent 71Ge extractions from the two Ga targets. The 71Ge production rates from the neutrino source were measured from July 2019 to March 2020. At the end of these measurements, the counters were filled with 71Ge doped gas and calibrated during November 2020. In this paper, results from the BEST sterile neutrino oscillation experiment are presented in details. The ratio of the measured 71Ge production rates to the predicted rates for the inner and the outer target volumes are calculated from the known neutrino capture cross section. Comparable deficits in the measured ratios relative to predicted values are found for both zones, with the 4σ deviations from unity consistent with the previously reported gallium anomaly. If interpreted in the context of neutrino oscillations, the deficits give best-fit oscillation parameters of Δm2=image.pngeV2 and sin22θ=image.png, consistent with νeνs oscillations governed by a surprisingly large mixing angle.




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