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

RIKEN Accel. Prog. Rep. 55 (2022)

International workshops on the extension project for the J-PARC
hadron experimental facility (J-PARC HEF-ex WSs)
F. Sakuma∗1 for the J-PARC HEF-ex WS Local Organizing Committee
International Workshops on the Extension Project
for the J-PARC Hadron Experimental Facility (J-PARCHEF-ex WSs) were held online on [ﬁrst] June 7–9, 2021,
and [second] February 16–18, 2022. The workshops wereorganized by Hadron Hall Users’ Association (HUA)
and supported by J-PARC Center, KEK Theory Center, RCNP, and RIKEN Nishina Center.
We have been extensively discussing a new plan for
the J-PARC Hadron Experimental Facility to extend
the existing experimental facility. The idea is to extend
the Hadron Hall to include another production target
downstream of the current production target and build
multiple new beamlines. Four new beamlines are being
planned to be constructed with the highest priority.
• A “high-intensity and high-energy-resolution beamline (HIHR)” and “high-purity and high-intensity lowmomentum charged K beamline (K1.1)” to solve theso-called hyperon puzzle through the super-precision
spectroscopy of Λ-hypernuclei and precise hyperonnucleon scattering measurement, respectively• A “high-intensity neutral KL beamline (KL2)” to explore new physics beyond the Standard Model by dramatically increasing the sensitivities of the kaon raredecay
• A “high-momentum particle-separated beamline(K10)” to resolve the conundrum of the strong interaction based on the investigation of Xi and Omega
baryons
We will develop new physics programs in particle and nuclear physics that cannot be implemented at the existing
facilities.
The J-PARC HEF-ex WSs were part of a series ofworkshops to discuss and detail the physics case at
the Hadron Experimental Facility. In the ﬁrst half of2021, several workshops were held focusing on the future physics case at the extended Hadron Experimental Facility; their outputs were summarized as the third
white paper.1) The extension project was reviewed by aninternational committee formed under J-PARC PAC in
August 2021 and was highly evaluated toward the early
realization of the facility extension. Detailed informationon the extension project can be found on HUA’s homepage.2)[First J-PARC HEF-ex WS on 7–9 June 2021]
The ﬁrst workshop was dedicated to discussions onimportant physics features at the extended J-PARC
Hadron Experimental Facility. This workshop included
plenary sessions by invited speakers, and the physics casefor the new beamlines was discussed.
 Project overview
 Strangeness nuclear physics at the HIHR and K1.1
∗1Fig. 1. The Second J-PARC HEF-ex WS.

beamlines Flavor physics at the KL2 beamline
 Hadron physics at the K10 beamline
The workshop included 138 participants from 12 countries (42 participants from abroad). There were 12 plenary talks. The full program and presentation ﬁles areavailable online at the workshop website.3)[Second J-PARC HEF-ex WS on 16–18 February 2022]
In the second workshop, discussions were dedicated tothe physics case connecting the “present” and “future”
Hadron Experimental Facility of J-PARC. For that purpose, this workshop covered wide-ranging topics related
to experimental and theoretical activities conducted at
the Hadron Experimental Facility.
 S = −1 and −2 hypernuclei
 Meson in nuclei Baryon spectroscopy
 Kaon rare decays
 μ-e conversion
 Future facilities and instrumentation
The scientiﬁc program comprised plenary sessions by invited speakers and parallel sessions by invited and contributed speakers. The workshop included 250 participants from 15 countries (94 participants from abroad).
There were 19 plenary talks and 86 parallel talks (including 23 invited keynote talks). The full program andpresentation ﬁles are available online at the workshop
website.4) A group photo is shown in Fig. 1.
Following the success of the workshops, we are planning to conduct the third workshop in FY2022 to continuously discuss physics at the J-PARC Hadron Experimental Facility and its extension.
References
1) Taskforce on the extension of the Hadron Experimental
Facility, arXiv:2110.04462.
2) http://www.rcnp.osaka-u.ac.jp/~jparchua/en/index.
html .
3) https://indico2.riken.jp/event/3773/ .
4) https://kds.kek.jp/event/40010/ (An access key is required.).

RIKEN Nishina Center- 187 -1