Improvement of systematic uncertainties for the neutron lifetime experiment at J-PARC

T. Mogi,a,∗ T. Hasegawa, K. Hirota, G. Ichikawa, S. Ieki, T. Ino, Y. Iwashita, S. Kajiwara, Y. Kato, M. Kitaguchi, f R. Kitahara, J. Koga, S. Makise, S. Matsuzaki, K. Mishima, K. Morikawa, N. Nagakura, H. Okabe, H. Otono, Y. Seki, j D. Sekiba, T. Shima, H. E. Shimizu, H. M. Shimizu, Y. Sugisawa, N. Sumi, H. Sumino, T. Tanabe, T. Tomita, H. Uehara, T. Yamada, S. Yamashita, K. Yano and T. Yoshioka Department of Physics, Graduate School of Science, The University of Tokyo, Tokyo, 113-0033, Japan Department of Physics, Graduate School of Science, Nagoya University, Nagoya, 464-8602, Japan KEK, High Energy Accelerator Research Organization, Tsukuba, 305-0801, Japan Research Centre for Neutrino Science, Tohoku University, Miyagi, 980-8578, Japan Institute for Integrated Radiation and Nuclear Science, Kyoto University, Kumatori, 590-0494, Japan f Kobayashi-Maskawa Institute for the Origin of Particles and the Universe (KMI), Nagoya University, Nagoya, 464-8602, Japan Department of Physics, Graduate School of Science, Kyoto University, Kyoto, 606-8502, Japan Department of Physics, Graduate School of Science, Kyushu University, Fukuoka, 819-0395, Japan Research Center for Advanced Particle Physics (RCAPP), Kyushu University, Fukuoka, 819-0395, Japan Center for Physics and Mathematics, Osaka Electro-Communication University, Osaka, 572-8530, Japan Institute of Applied Physics, University of Tsukuba, Tsukuba, 305-8573, Japan Research Center for Nuclear Physics (RCNP), Osaka University, Ibaraki, 567-0047, Japan School of High Energy Accelerator Science, The Graduate University for Advanced Studies, Tsukuba, 305-0801, Japan Department of General Systems Studies, Graduate School of Arts and Sciences, The University of Tokyo, Tokyo, 153-8902, Japan International Center for the Elementary Particle Physics (ICEPP), The University of Tokyo, Tokyo, 113-0033, Japan E-mail: mogi@icepp.s.u-tokyo.ac.jp The neutron lifetime is one of the important parameters for particle physics and astrophysics. There is a 4.6σ (9.5 s) discrepancy between the results of the two typical methods. To solve this discrepancy, a new neutron lifetime experiment with a different method is in progress at J-PARC, and this experiment published the first result in 2020 of 898±10(stat.) +15/−18(syst.) s. We have performed improvements to reduce systematic uncertainties towards 1 s accuracy. The methods to measure the amount of 3He injected and in the working gas have been upgraded, and a new model for the space charge effect in the Monte Carlo simulation has been implemented.