Ⅱ-9. Instrumentation
RIKEN
Accel. Prog. Rep. 56 (2023)

RIKEN Accel. Prog. Rep. 56 (2023)

Status of the J-PARC E16 experiment in 2022
S. Yokkaichi∗1 for the J-PARC E16 Collaboration
We proposed the experiment E161) to measure thevector meson decays in nuclei in order to investigate
the chiral symmetry restoration in dense nuclear matter. The experiment started at the J-PARC Hadron
Experimental Facility.
This experiment aims to systematically study thespectral modiﬁcation of vector mesons in nuclei, particularly the ϕ meson, using the e+ e− decay channel
with statistics that are two orders larger in magnitude
than those of the prior E3252) experiment performed atKEK-PS. In other words, it aims to accumulate 1 ×105
to 2×105 events for each nuclear target (H, C, Cu, andPb) and deduce the dependence of the spectral modiﬁcation on the size of nucleus and meson momentum.
The number of modiﬁed mesons could be larger forlarger nucleus and lower momentum mesons because
the decay probability inside the nucleus is enhancedfor such cases.
The proposed spectrometer comprises 26 modules.
As shown in Fig. 1, a module consists of Lead-glass
calorimeter (LG) and Hadron-blind detector (HBD)
for electron identiﬁcation, as well as three-layers ofGEM Trackers (GTR) and a single layer of silicon strip
detector (SSD) as the tracking devices.

Fig. 1. Cross-sectional plan view of the E16 spectrometerin the eight-module conﬁguration for Run-1.

Commissioning runs, in total 403 hours as summarized in Table 1, were performed in 2020-21 at thenewly constructed ‘High-momentum beam line’.3) Owing to budget limitations, a limited number of modules were installed in the commissioning runs. In
these runs, electron identiﬁcation performance wasconﬁrmed.4) The read out circuit for the data collection is described in Ref.5)
In the next beam time planned in 2023, full eight
modules shown in Fig. 1 will be operated. In the previous runs, six modules of SSD was borrowed from
J-PARC E07 group. However, they will be replaced∗1

Table 1. Run-time summary.
prospect.

Run-0a Run-0b
Run-0c Total
2020
2021
2021
Period
6/4-20 2/11-28 5/28-6/9
Days
17181247Beam time (h)159110134403Raw data (TB)
33
28
46
97- 111 -Run-0d2023(5-6)
100-by the newly developed eight modules with the cooperation of the CBM group at GSI.
The major issue detected in the commissioning runs
is the micro beam structures, which deteriorate theDAQ performance3) due to the time-localized highbeam intensity. It was typically ten times as highas the nominal value of the beam intensity. In otherwords, the typical beam rate is 5 GHz because the intensity is 1 × 1010 protons per 2 sec duration; however,
the actual beam rate increased to 50 GHz locally due
to the micro structures.
Some countermeasures have been discussed and will
be applied in the next beam time. Before Run-1(physics run), we plan to perform a beam study tocheck whether the countermeasures can improve theDAQ performance, and construct the acceptable trigger rate by tuning threshold, coincidence pattern andtime window, and beam intensity, with the upgraded
DAQ system.
In Aug. 2022, our proposal for Run-1 based on theupdated technical design report was reviewed. The
approval for Run-1 was deferred, and only 200 hours
of beam time was approved for the beam study (101hours) and trigger study (100 hours) as mentioned
above.
In J-PARC, an upgrade work of MRa) was performed
from 2021 summer (just after the Run-0c) to 2022 autumn, and a test operation of MR had started. Owing
to the malfunction of the septum magnet and so on, weexpect the next beam time, namely, a slow extraction
beam for users, in May 2023 at the earliest case.
References1) S. Yokkaichi et al., J-PARC proposal No. 16(http://j-parc.jp/researcher/Hadron/en/pac_0606/pdf/p16-Yokkaichi_2.pdf); M. Ichikawa et al., Acta
Phys. Pol. B Proc. Suppl. 16, 1-A143 (2023).
2) R. Muto et al., Phys. Rev. Lett. 98, 042501 (2007).
3) S. Yokkaichi, RIKEN Accel. Prog. Rep. 55, 54 (2022).
4) S. Nakasuga et al., Nucl. Instrum. Methods Phys. Res.
A 1041, 167335 (2022).
5) T. N. Takahashi et al., IEEE Trans. Nucl. Sci. 68, 1907(2021).
a)

RIKEN Nishina Center

Run-0d demonstrates

J-PARC Main Ring Accelerator