V. EVENTSRIKEN Accel. Prog. Rep. 55 (2022)

RIKEN Accel. Prog. Rep. 55 (2022)

SPIN2021 international spin symposium
Y. Goto∗1 and T. Uesaka∗1 for the SPIN2021 Local Organizing Committee
The 24th International Symposium on Spin Physics(SPIN2021) was held at the Kunibiki Messe Convention Center in Matsue, Shimane Prefecture, Japan inOctober 18–22, 2021. We aimed to cover a wide rangeof topics related to particle and nuclear spin physics
from low energy to high energy, including experimental, theoretical, computational and technological aspects and applications.
This symposium was originally scheduled to be heldin 2020 as SPIN 2020; however, it was postponed because of the COVID-19 pandemic. This symposium
series has been held jointly since 2000, combining theHigh Energy Spin Symposia and Nuclear Polarization
Conferences. The most recent symposia took place inDubna, Russia (2012); Beijing, China (2014); Urbana
Champaign, USA (2016); and Ferrara, Italy (2018).
The symposium was held in a hybrid style, i.e., inperson and online participation were possible. As aresult, in-person on-site participation was limited tothe symposium organizers, which was 20 people, while
online participation included about 160 presenters and150 audience participants. The total number of participants was about 330, which is a larger number forthis symposium series.
The hybrid style was useful to invigorate our scientiﬁc discussions under the present situation of thepandemic. We had successfully tested the hybrid stylewith a domestic workshop on spin physics.1) In the hybrid style of the SPIN2021 symposium, the structure of
the plenary and parallel sessions was set up to be convenient for online participants residing outside Asia. In
the ﬁrst two days, the symposium started at 3 p.m. tofacilitate online participation from Europe, and in thelast two days, it started at 7 a.m. to facilitate online
participation from the United States.
The scientiﬁc program of SPIN 2021 included topics related to spin phenomena in particle and nuclear
physics and related ﬁelds. The following symposium
topics were covered:• Nucleon helicity structure• 3D structure of the nucleon:transversemomentum dependent distribution• 3D structure of the nucleon: general parton distribution• Fundamental symmetries and spin physics beyond
the Standard Model• Spin physics in nuclear reactions and nuclei• Low energy spin physics with lepton, proton andhadron probes• Future facilities and experiments• Acceleration, storage and polarimetry of polarized∗1Fig. 1. Online participants of the SPIN2021 symposium.

beams• Polarized ion and lepton sources and targets• Applications of nuclear polarization techniques toother ﬁelds
The symposium format comprised discussions in plenary and parallel sessions. The plenary session beganwith a discussion on the recent major topic of muong-2 measurements, and two more special discussions
on spintronics and polarization measurements of thecosmic microwave background took place. In total, 29
plenary talks were given. Parallel sessions were held forthe aforementioned listed topics, with up to ﬁve sessions running in parallel. Few sessions were conducted
as joint sessions for multiple topics.
The symposium is hosted by RIKEN Nishina Centerand co-hosted by KEK, J-PARC, RCNP Osaka University, CNS University of Tokyo, and Yamagata University. Moreover, it is supported by RIKEN as a partof the RIKEN Symposium Series, and subsidy system
for international conferences in Matsue and Shimane
Prefecture.
A screenshot of online participants (not all the participants) is shown in Fig. 1. The full program and presentation slides presented in the sypmposim are available at the symposium website (https://indico2.
riken.jp/event/3082/), and the proceedings of theSPIN2021 symposium will be pulished in the JPS Conference Proceedings.
Reference1) Y. Goto, RIKEN Accel. Prog. Rep. 54, 197 (2021).

RIKEN Nishina Center- 188 -1