Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 47 (2014)

Development of MWDC readout system for the spectroscopy
experiment of η ′ mesic nuclei at GSI and FAIR
H. Yamakami,∗1,∗2 K.-T. Brinkmann,∗3 S. Friedrich,∗3 H. Fujioka,∗1,∗2 H. Geissel,∗1,∗4 R.S. Hayano,∗5K. Hosomi,∗6 Y. Igarashi,∗7 K. Itahashi,∗1 M. Iwasaki,∗1 V. Metag,∗3 T. Nagae,∗2 M. Nanova,∗3 T. Nishi,∗1,∗5H. Outa,∗1 K. Suzuki,∗1,∗8 T. Suzuki,∗5 Y.K. Tanaka,∗1,∗5 Y.N. Watanabe,∗1,∗5 and H. Weick∗1,∗4The η ′ (958) meson has an exceptionally large mass,compared with other pseudoscalar meson such as pions. Theoretically, it has been pointed out that a large
mass reduction (∼100 MeV) is expected at the normal
nuclear density, which leads to existence of an η ′ mesic
nucleus, a bound state of an η ′ meson and a nucleus.
From an experimental observation of η ′ mesic nuclei,
we may take the ﬁrst step to understand the η ′ mass
generation mechanism1) . For this purpose, we perform
spectroscopy of η ′ meson bound states in 11 C nuclei
by missing-mass measurement of the 12 C(p, d) reaction near the η ′ production threshold at the GSI-SISfacility2) .
In this experiment, a 2.5 GeV proton beam extracted
from SIS synchrotron will be injected into a 12 C target, and the ejectile deuterons with the momenta of∼ 2.8 GeV/c are momentum-analyzed by the fragment
separator(FRS) at a dispersive focal plane with detection of the tracks by two sets of multi-wire drift chamber MWDCs. The ﬁrst experiment is scheduled in July2014.
We are working on upgrading the current DAQ system, particularly the readout of MWDCs. We willadopt a 64ch all-in-one readout board equipped withASD, Flash ADC, and TDC. Almost all the digitalprocesses are designed in the FPGA. This board was
originally designed for Belle-II Central Drift Chamber(CDC)3) . According to Ref. 3), they achieved a deadtime of about 0.5% at a trigger rate of 10 kHz in atest experiment. This is approximately a factor 10 improvement compared to the current (our) system.
The digitalized data are transferred through a network with the SiTCP4) sub-system, which is an implementation of TCP/IP on FPGA. We have been customizing the FPGA program and investigating the potential of the board. In case that the readout board isequipped with performance of reading data at a several kHz trigger, the quality and the quantity of theexperimental data will exhibit signiﬁcant improvementcompared to that of the VME based DAQ without thereadout board.
The readout board is being updated, so as to operate

under a trigger distribution system, which is alreadyadopted in J-PARC hadron experiments. Along withreadout boards, we are developing a new ”sub triggermodule” (STM), for distributing trigger information
including the event tag to each readout board. The
distribution system with STM is useful to ensure theevent matching and to avoid overlooking event slips
among diﬀerent DAQ subsystems.
We will make a performance test of the readoutboard with respect to the radiation tolerance and theDAQ rate, exploiting the opportunity of beamtime at
GSI in July, 2014. By loosening the trigger condition,
the performance under a high trigger rate will also beevaluated.
In summary, we will introduce a network-based DAQwith the readout board for MWDCs in the η ′ experiment at GSI beyond 2014 and FAIR, which is currently
under construction. As it will enable us to handle ahigher trigger rate, a high-statistics measurement will
be possible by using a more intense beam and/or athicker target.

∗1References

∗2
∗3
∗4
∗5
∗6
∗7
∗8

RIKEN Nishina Center
Department of Physics, Kyoto University
Universität Gießen
GSI
Department of Physics, University of TokyoJapan Atomic Energy Agency
Institute of Particle and Nuclear Studies, KEK
Stefan-Meyer-Institut für subatomare Physik

Fig. 1. View of 64ch Readout Board.

1) H. Nagahiro, D. Jido, H. Fujioka, K. Itahashi, andS. Hirenzaki : Phys. Rev. C 87, 045201 (2013).
2) K. Itahashi et al.: Prog. Theor.Phys. 128, 601 (2012).
3) N. Taniguchi et al.: Nucl. Inst. Meth. 732, 540 (2013).
4) T. Uchida : IEEE Transaction on Nuclear Science, vol.
55, no. 3, June 2008.

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