RIKEN Accel. Prog. Rep. 50 (2017)

Ⅱ-9. Instrumentation

Preparation status of the J-PARC E16 experiment in 2016
S. Yokkaichi∗1 for the J-PARC E16 Collaboration
We have proposed the experiment E161) to measure
the vector meson decays in nuclei in order to investigate the chiral symmetry restoration in dense nuclear matter. The experiment will be performed at
the J-PARC Hadron Experimental Facility. Scientiﬁc(“stage 1”) approval was granted to the experimentE16 by PAC in March 2007. For the full approval,
we were required to demonstrate the experimental feasibility and show the prospects of acquiring suﬃcient
funds and of beam-line construction. Toward the fullapproval, the technical design report was submitted
to PAC in May 2014, and the revision was performed
twice, as per the requirements of PAC. The most recent
revision has been submitted to PAC in Jan. 2017.
The aim of the experiment is to perform to systematically study the spectral modiﬁcation of vector mesons,particularly the φ meson, in nuclei by using the e+ e−
decay channel with statistics that are two orders larger
in magnitude than those of the precedent E3252) experiment performed at KEK–PS. In other words, theaim is to accumulate 1 × 105 to 2 × 105 events for eachnuclear target (H, C, Cu, and Pb) and to deduce thedependence of the modiﬁcation on the matter size andthe meson momentum. At the same time, the e+ e−
decays of the ρ, ω, and J/ψ mesons can be measured,
while the yields depend on the trigger condition required to suppress the background e+ e− pairs.
In order to increase the statistics by a factor of 100,
we plan to use a 30-GeV primary proton beam with
1 ×1010 particle per spill (2-s duration and 5.52-s cycle) of in the high-momentum beam line and 0.2%interaction targets, which brings a background particle
rate of 5 kHz/mm2 at the most forward region of thetrackers. In order to cope with such a high rate, theGEM tracker has been adopted. a)
The construction of the high-momentum beam line,
where we will perform the experiment, was started in
JFY 2013 by KEK and scheduled for completion inJFY 2015. However, the construction has been delayed owing to a radiation accident at J-PARC in May
2013 and the budgetary limitation partly caused by theaccident. The current target date of the ﬁrst beam isMar. 2019 in the most optimistic scenario. While sucha tight budgetary situation, the spectrometer magnet
reconstruction was completed in JFY 2015 by KEK.
Our spectrometer has 26 modules. Owing to thebudget limitations, our ﬁrst goal of the staged construction plan is to construct eight modules, which
covers approximately one third of the full acceptance.
The development of the detectors was completed,∗1a)

RIKEN Nishina Center
At the COMPASS experiment, the GEM tracker was operated at a particle rate of 25 kHz/mm2 .8)- 218 -and we have been in the production phase since 2013.
For the GEM Tracker (GTR),3) the production ofGEM and the read-out strip board has been underway since 2013. Parts for six modules (out of eight, asmentioned above) have been completed. The CFRP
frames, which are used to install the GEM chambersin the spectrometer, have also been made for two modules. For the HBD,4) which is one of our electron ID
detectors, two modules are currently under construction at RIKEN. The read-out electronics including preampliﬁer for the two GEM detectors, GTR and HBD,
have also been purchased, for six and two modules, respectively. They use an APV25 chip and SRS, bothof which are CERN-made. We joined the RD515) collaboration in CERN which aims to develop multi-pixel
gas detectors including GEM.
The lead-glass (LG) EM Calorimeter, another electron ID detector, utilizes the recycled LG from theTOPAZ experiment. The reshaping of LG blocks foreight modules (330 blocks) was completed at the KEK
engineering center. Electronics for two modules has
been purchased, and it uses the DRS4 chip.6)
The development of trigger electronics is still underway.7) The trigger signal for vector mesons consists of
two electron candidates. An electron candidate is deﬁned by the coincidence of corresponding hits in LG,HBD, and the outermost layer of GTR, located immidiately in front of HBD. ASICs for the amp-shaperdiscriminator to generate the trigger primitive of thetwo GEM detectors have been produced in cooperation
with the KEK e-sys group. To generate a global trigger
signal, an FPGA board “UT3”(developed by Belle II)
is used. To transfer the trigger primitives to UT3, wedeveloped another module called “TRG-MRG.” Thedevelopment of ﬁrmware for these modules is underway, and a system test connecting all the modules with
detectors is planned for the end of JFY 2017.
References
1) S. Yokkaichi et al., J-PARC proposal No. 16(http://j-parc.jp/researcher/Hadron/en/pac_0606/
pdf/p16-Yokkaichi_2.pdf),
Y. Morino et al., JPS Conf. Proc. 8, 022009 (2015).
2) R. Muto et al., Phys. Rev. Lett. 98, 042501 (2007).
3) W. Nakai et al., RIKEN Accel. Prog. Rep. 49, 195(2015).
4) K. Kanno et al., Nucl. Instrum. Meth. A 819, 20-24(2016).
5) http://rd51-public.web.cern.ch/RD51-Public/6) https://www.psi.ch/drs/drs-chip/7) T. N. Takahashi et al., J. Phys.: Conf. Ser. (JPCS)
664, 082053 (2015).
8) B. Ketzer et al., Nucl. Instrum. Meth. A 535 314-318(2004).