II-4. Hadron Physics

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Expression of interest for EIC-Japan
Y. Goto,∗1 Y. Akiba,∗1 I. Nakagawa,∗1 and R. Seidl∗1 for the EIC-Japan GroupThe Electron-Ion Collider (EIC) is a great research
opportunity for Japan, and we are working to form aJapanese group (EIC-Japan). We will form a highenergy accelerator-based experimental group in theﬁeld of both nuclear and particle physics. In responseto the “Call for Expressions of Interest (EOIs) for Potential Cooperation on the EIC Experimental Program” by BNL and JLab, we submitted an EOI bythe EIC-Japan group in November, 2020. The EOI isnon-binding, and its purpose is to guide expectations
and better understand the potential EIC experimental
equipment scope.
In Japan, the Science Council of Japan (SCJ) developed a master plan for large-scale research programs inacademia (Master Plan 2020) in 2019–2020. The EIC
was recognized as an important international collaborative research project with a long-term research planby the Future Planning Committee of the Committee
on Nuclear Physics, and it was proposed to the MasterPlan. Consequently, the EIC was selected as an academic major research project although it was not yet
selected as a priority project in the Master Plan 2020.
The EIC-Japan group plans to design and construct forward detectors of the EIC detector, especially calorimeters, to lead the study on forward andvery forward physics. Forward detectors are one of themost important detectors for precisely reconstructing
certain events of the deep inelastic scattering (DIS)
process, which is the basis of all research at the EIC.
We can precisely determine the spin and internal orbital motion of partons in the nucleon, which is still
poorly understood, by measuring the forward and mostforward jets, hadrons, photons, and electrons and by
studying their correlations. In particular, the contribution of gluons, sea quarks, and orbital angular momentum to the proton spin remains a mystery. In addition, our understanding of the most forward events
is expected to greatly enhance the development of
QCD-based event generators. Further, this will greatly
contribute to eliminating uncertainties in other highenergy particle experiments and cosmic ray observations.
We participated in the development of the forwardhadron calorimeter,1) which is essential for forward
jet reconstruction and hadron energy measurements,
as well as triggering. Designing and developing thecalorimeter is a joint project with the EIC genericdetector R&D group eRD1 and the STAR upgrade
project. A prototype calorimeter developed as theSTAR forward calorimeter comprises 38 layers of ironabsorbers and plastic scintillator plates. A wavelength∗1

shifting (WLS) plate provides uniform and eﬃcient
light collection from all scintillation tiles along thedepth of the tower. The light from the WLS plateis measured with SiPMs.
√ Since the energy resolutionof this detector is 70%/ E(GeV)) with an additional
constant term, the one for the EIC requires higher energy resolution.
We proposed the development of a zero-degree apparatus in the EIC experiment,2) and it has been approved as eRD27 this year. Zero degree detectors serve
critical roles for a number of important physics topics at the EIC. We study the requirements and technologies of zero-degree detectors, and we develop a
position-sensitive zero-degree calorimeter (ZDC). In
this program, we will conduct 1) a photon detector
study at a low energy <300 MeV, cooperating witheRD1 for crystal and glass scintillators; 2) a prototype study of ZDC with position sensitivity, with theALICE-FoCal technology and the LHC-ZDC technology with fused silica; and 3) a radiation hardness studyof scintillators.
Subsequently, in addition to the proposals in themaster plan, we have expanded our activities as aJapanese group to include a group interested in building a silicon tracking detector. The team is open tonew collaborators. Heavy ﬂavor quarks are highlighted
at the EIC as the ideal probe to study open questions
in QCD, such as mass and ﬂavor dependence of energy
loss, fragmentation and hadronization modiﬁcation ina nuclear medium, nuclear parton distributions, andso on. Silicon sensor detectors are the key technology
employed for heavy ﬂavor detection by observing theirdecay vertex precisely. The performance of silicon sensors thus plays a crucial role in pursuing the research inheavy ﬂavor physics at a satisfactory level. We propose
to apply a silicon sensor based on silicon-on-insulator
monolithic pixel (SOIPIX) detector technology3) thathas been developed by the KEK group. SOIPIX has
demonstrated the world’s best tracking resolution of0.680 ± 0.006 µm in a silicon detector using 120 GeV
FNAL’s test beam. Further SOIPIX is employed as
the inner vertex detector of 4π silicon hybrid detector
proposed by ANL and BNL collaborators.
References

1) Y. Goto et al., RIKEN Accel. Prog. Rep. 52, 87 (2019).
2) Y. Goto et al., RIKEN Accel. Prog. Rep. 53, 82 (2020).
3) Y. Arai et al., Nucl. Instrum. Methods Phys. Res. A636, S31–S36 (2011).

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