J-PARC E16 experiment

Measurements of spectral change of vector mesons in nuclei

In order to explore the chiral symmetry in nuclear matter, we measure the mass modification of vector mesons in nuclei systematically. We construct a large acceptance di-electron spectrometer at the high-momentum beam line in the J-PARC hadron facility.

Publications and presentations

Current status(2026/Apr)

First physics paper is published in Mar. 2026, which is based on the data taken in the trigger-study run (Run-0e) in May 2024.
First physics Run (Run-1a) was performed in November 2025 and under analysis. Due to the fire in J-PARC in April 2026, next run is postponed to Autumn 2026 or later.

Just after the first comissioning run (Run-0a), 2020/June/22

Proposal pdf(2006/6)

Run0(Commissioning Run) Proposal pdf(2017/6)

Schematic view of the proposed spectrometer	Spectromter magnet at the J-PARC hadron facility(2015).	Spectrometer, from the upstream (2020).

Prototype of GEM chambers	production type of GEM chambers	Assembled single module of GEM Traker

Prototype of a hadron blind Cherenkov detector	1st production type of HBD	A HBD gas vessel (for two modules) to be installed

preamp for GEM Tracker using APV25	prototype FEM for the lead-glass EMcal	Trigger-signal merging module[taken from IEEE TNS 66(2019)2022]

24ch-ASD for the trigger signal from GTR	9ch-ASD for the trigger signal from HBD (with two CERN APV hyblid preamp cards )

SSD borrowed from the J-PARC E10/E03 group, operated 2020-21	SSD located inside the GTR	new SSD ("STS") developed with the CBM-STS group, being operated since 2023

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アウトリーチ活動(OUTREACH, in Japanese)

Collaboration (2026/Apr)

S. Yokkaichi*, H. En'yo, M. Ichikawa, W. Nakai, T. N. Murakami, F. Sakuma (RIKEN Nishina Center)
K. Aoki, R. Honda, Y. Morino, R.Muto, K. Ozawa, S. Sawada, M. Sekimoto(KEK)
S. Nagafusa, S. Nakasuga, M. Naruki, S. Hashimoto (Kyoto University)
H. Noumi, K. Shirotori, T. N. Takahashi, T. Akaishi, S. Ashikaga (RCNP, Osaka Univ.)
H. Hamagaki (NiAS)
K. Shigaki, Y.L.Yamaguchi (Hiroshima University)
A. Kiyomichi (JASRI)
T. Sakaguchi (BNL)
H. Sako, S. Sato, W.S. Jung, R. Sato, F. Oura, G. Nukazuka (JAEA)
T. Chujo, S. Esumi, T. Nonaka (Tomonaga Center, University of Tsukuba)
S. Kajikawa (Tohoku University)
R. Ejima (CNS, U-Tokyo)
W.-C. Chang, C.-H Lin (Academia Sinica)
J. Heuser, A.R.Rodriguez, M.Teklishyn (GSI)
A. Toia, D.R.Garces (Goethe University/GSI)

* : Spokesperson

This project is supported by RIKEN, KEK,

KAKENHI (JSPS/MEXT, JAPAN), Grant Numbers:

19340075 : 2007-2008: Prototyping of electron identifier for precise measruement of chiral condensate in nuclei (S. Yokkaichi)
19654036 : 2007-2008: Development of large-aperture light detector using GEM for the two-dimensional imaging (K. Ozawa)
21105004 : 2009-2013: Experimental investigation of the hadron mass generation mechanism due to the breaking of the chiral symmetry (H. En'yo)
12J01196 : 2012-2014: Systematic study of the mass modification of vector mesons in nuclei (D. Kawama)
14J08572 : 2014-2016: Study of hadron-mass generation via high-precision measurement of vector-meson mass in nuclei (Y. Obara)
26247048 : 2014-2016: Measurements of the meson-mass modification in nuclei due to the partial restoration of the chiral symmetry (S. Yokkaichi)
15K17669 : 2015-2016: Development of a fast readout for the EM calorimeter to measure the meson mass modification in nuclear media (T. N. Takahashi)
15H05449 : 2015-2017: Research of the origin of hadron mass at J-PARC (K. Aoki)
18J20494 : 2018-2020: Experimental study of mass-generation mechanism through the dilepton measurement (S. Ashikaga)
18H05235 : 2018-2022: Origin of hadron mass studied by the systematic measurement of spectral change of mesons in nuclei (S. Yokkaichi)
19K03898 : 2019-2021: Study of Vector Meson Production in Nuclear Medium via K-meson Decay Mode (S. Sato)
20H05647 : 2020-2024: Clear measurements of meson mass modifications in nucleus by using high intensity proton beam (K. Ozawa)
20H01935 : 2020-2023: Study of five quark state including c-cbar pair in nucleon at J-PARC (Y. Morino)
21H00128 : 2021-2022: Establishment of phi->KK measusurement method in pA collisions at J-PARC (H. Sako)
21H00134 : 2021-2022: Precise dilepton measurement for the study of quark-pair correlation in finite-density media(T. N. Takahashi)
21H01102 : 2021-2023: Systematic study of the restoration of chiral symmetry (K.Aoki)
23KJ1223 : 2023-2024: Experimental study of mass generation through the mass measurement of phi-meson at high density (S. Nakasuga)
23H05440 : 2023-2027: Precise measurement of di-electron decay of mesons and the chiral condensate in nuclei (S. Yokkaichi)
23KJ1650 : 2023-2025: Study of generation mechanism of hadron mass using machine lerning and mass-degeneration of chiral partner (R. Ejima)
24H00236 : 2024-2027: Study of the origin of hadron mass through dilepton measurement (K.Aoki)

and Ministry of Science and Technology of Taiwan, Grant number:

MOST108-2112-M-001-020

Links

yokkaich-at-riken.go.jp

Last modified: Sun Jun 28 21:40:33 2026

J-PARC E16 experiment

Measurements of spectral change of vector mesons in nuclei

Publications and presentations

Current status(2026/Apr)

Proposal pdf(2006/6)

Run0(Commissioning Run) Proposal pdf(2017/6)

Schematic view of the proposed spectrometer

Spectromter magnet at the J-PARC hadron facility(2015).

Spectrometer, from the upstream (2020).

Prototype of GEM chambers

production type of GEM chambers

Assembled single module of GEM Traker

Prototype of a hadron blind Cherenkov detector

1st production type of HBD

A HBD gas vessel (for two modules) to be installed

preamp for GEM Tracker using APV25

prototype FEM for the lead-glass EMcal

Trigger-signal merging module[taken from IEEE TNS 66(2019)2022]

24ch-ASD for the trigger signal from GTR

9ch-ASD for the trigger signal from HBD (with two CERN APV hyblid preamp cards )

SSD borrowed from the J-PARC E10/E03 group, operated 2020-21

SSD located inside the GTR

new SSD ("STS") developed with the CBM-STS group, being operated since 2023

アウトリーチ活動(OUTREACH, in Japanese)

Collaboration (2026/Apr)

Links