2021 Fiscal Year Final Research Report

Search for new interaction via neutron-nano-particle scattering

Research Project

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Project/Area Number	19H01927
Research Category	Grant-in-Aid for Scientific Research (B)
Allocation Type	Single-year Grants
Section	一般
Review Section	Basic Section 15020:Experimental studies related to particle-, nuclear-, cosmic ray and astro-physics
Research Institution	Osaka University
Principal Investigator	Shima Tatsushi 大阪大学, 核物理研究センター, 准教授 (10222035)
Co-Investigator(Kenkyū-buntansha)	三島賢二大学共同利用機関法人高エネルギー加速器研究機構, 物質構造科学研究所, 特別准教授 (20392136) 吉岡瑞樹九州大学, 先端素粒子物理研究センター, 准教授 (20401317) 北口雅暁名古屋大学, 素粒子宇宙起源研究所, 准教授 (90397571)
Project Period (FY)	2019-04-01 – 2022-03-31
Keywords	重力 / 逆二乗則 / 余剰次元 / ナノ粒子 / 中性子散乱
Outline of Final Research Achievements	The small-angle neutron scattering (SANS) is useful to search for gravity-like new interactions in the sub-micron range, since it is free from the disturbances by the electromagnetic interaction. In this research, nano-particles were employed as the target of SANS, since the experimental sensitivity to new interactions are enhanced by six orders of magnitude thanks to the coherent scattering. To suppress the background due to nuclear scattering, we developed nano-particles made of vanadium whose coherent neutron scattering cross section is minimum among all the elements. With this material, a SANS experiment was performed at the J-PARC, achieving the sensitivity comparable to the previous experiments. To get a more better sensitivity, we developed nano-particles having extremely small neutron scattering cross section by mixing vanadium and nickel that have opposite signs of coherent scattering lengths. The SANS experiment with this new material is scheduled in June, 2022.
Free Research Field	素粒子実験・原子核実験
Academic Significance and Societal Importance of the Research Achievements	重力は距離の二乗に反比例する、すなわち逆二乗則に従うと考えられているが、「大きな余剰次元模型」などの理論は、極めて短い距離で逆二乗則が破れる可能性を示唆している。重力の逆二乗則は主に原子・分子で構成された物体間の力を測ることで検証されてきたが、１μm以下の距離では分子間力の影響で実験感度が急激に失われるという問題があった。我々は分子間力を受けない中性子と物体との散乱を用いることでこれを解決した。特に散乱標的として、別の擾乱の原因である原子核散乱が極めて弱いバナジウム、およびバナジウム-ニッケル合金を材料とするナノ粒子を開発し、従来よりも10倍以上高い感度での逆二乗則の検証への道を拓いた。