Performance of the Fully Equipped Spin Flip Chopper for the Neutron Lifetime Experiment at J-PARC

• Published in: Progress of theoretical and experimental physics 2024-09, Vol.2024 (9)
• Main Authors: Mishima, K, Ichikawa, G, Fuwa, Y, Hasegawa, T, Hino, M, Hosokawa, R, Ino, T, Iwashita, Y, Kitaguchi, M, Matsuzaki, S, Mogi, T, Okabe, H, Oku, T, Okudaira, T, Seki, Y, Shimizu, H E, Shimizu, H M, Takahashi, S, Tanida, M, Yamashita, S, Yokohashi, M, Yoshioka, T
• Format: Article
• Language: English
• ISSN: 2050-3911; 2050-3911
• DOI: 10.1093/ptep/ptae123

Abstract To solve the “neutron lifetime puzzle,” where measured neutron lifetimes differ depending on the measurement methods, an experiment with a pulsed neutron beam at J-PARC is in progress. In this experiment, neutrons are bunched into 40-cm lengths using a spin flip chopper (SFC), where the statistical sensitivity was limited by the aperture size of the SFC. The SFC comprises three sets of magnetic supermirrors and two resonant spin flippers. In this paper, we discuss an upgrade to enlarge the apertures of the SFC. With this upgrade, the statistics per unit time of the neutron lifetime experiment increased by a factor of 2.8, while maintaining a signal-to-noise ratio of 250–400, which is comparable to the previous one. Consequently, the time required to reach a precision of 1 s in the neutron lifetime experiment was reduced from 590 to 170 days, which is a significant reduction in time. This improvement in the statistics will also contribute to the reduction of systematic uncertainties, such as background evaluation, fostering further advancements in the neutron lifetime experiments at J-PARC.