II-4. Hadron Physics

RIKEN Accel. Prog. Rep. 55 (2022)

RIKEN Accel. Prog. Rep. 55 (2022)

Design of the zero degree calorimeter for the EIC
S. Shimizu,∗1,∗2 Y. Goto,∗1 and Y. Yamazaki∗3 for the EIC Japan group and the EIC eRD27 collaboration
The Electron Ion Collider (EIC) is a future particle collider scheduled for construction in the US. By
colliding electrons and protons or nuclei, the EIC will
be a powerful tool to examine the structure inside ofprotons and nuclei. A new electron beam facility isplanned to be built and will be operated together withthe existing ion beams at the Brookhaven NationalLaboratory. The expected beam energies are 5–18 GeV
for electrons and 41–275 GeV for protons, providing
the highest centre-of-mass energy of 141 GeV. The EIC
will cover a large kinematic region, which allows for theinvestigation of the parton dynamics in protons andnuclei.
In some of the key EIC physics programs,1) it isessential to detect hadrons or photons from collisions
in the far-forward region of the ion-beam direction. A
suite of detectors will be placed there, in addition tothe central detector at the collision point. The ZeroDegree Calorimeter (ZDC) is one of the far-forward
detector systems and will detect photons and neutrons.
It will be placed ∼40 m downstream of the collision
point, with an aperture of ∼4.5 mrad.
The ﬁrst ZDC design is considered based on thephysics requirements for the ZDC. Examples of measurements that need the ZDC are as follows:1)

Fig. 1. ZDC design. Particles arrive from the left sideof the ﬁgure. The detector consists of a 7 cm crystallayer (yellow) with a silicon pixel layer attached in front(magenta), 22 layers of tungsten/silicon planes (lightpurple) with an additional silicon pixel layer in front,
12 layers of lead/silicon planes (gray), and 30 layersof lead/scintillator planes (green), corresponding to a
thickness of 8X0 , 22X0 , 2λI , and 5λI , respectively. The
total size is 60 cm × 60 cm × 162 cm. The segmentation
on each layer is as follows: 3 cm × 3 cm for the crystal,
1 cm×1 cm for standard silicon layers, 3 mm×3 mm forsilicon pixel layers, and 10 cm × 10 cm for scintillators.

The Crystal calorimeter is intended for the energy
measurement of low-energy photons.
The W/Sicalorimeter will measure the rest of the photon energy
and the shower development of photons and neutrons.
Silicon pixel layers are inserted for position measurement. Silicon layers are used in the Pb/Si calorimeterfor radiation hardness and for the neutron shower measurement. The last Pb/Sci calorimeters are intended
to measure the neutron energy.
The design is studied and optimized using theGeant44) simulation. The simulation has a few missingpieces, e.g., no readout materials included for crystals
and scintillators. However, it allows the study of baseline performance of the detector complex. Figure 1
shows the optimized design. The performance is studied against single photons and single neutrons. It has
an energy resolution better than the requirement anda position resolution for photons better than 2 mm.
The design will be further optimized based on its
cost, radiation hardness, and the full simulation. The
optimization includes the choice of materials for thecrystal, such as PbWO4 (this study) and LYSO.

• Exclusive vector meson production in e + A collisions, which is sensitive to gluon saturation,2)• Spectator-neutron-tagged e+d deep inelastic scattering, which is sensitive to the nuclear eﬀect indeuterons,• Meson structure measurements,• Leading neutron measurements.
The required performance is as follows:• Tagging of O(100) MeV photons with >90% eﬃciency and an energy resolution of 20–30%,• Detection of 20–40 GeV photons with an energy
and a good position resoluresolution of √ 35%
E(GeV)

tion of O(1) mm,• Detection of neutrons with energy up to theion beam energy with an energy resolution of√ 50% + 5%, a position resolution of √3mrad ,E(GeV)

and a large lateral size of 60 cm × 60 cm.

E(GeV)

To fulﬁll these requirements, the ZDC is designed as
a complex of detectors, namely a Crystal calorimeter and three types of sampling calorimeters: ALICE
FoCal-E3) style Tungsten-Silicon (W/Si), Lead-Silicon(Pb/Si), and Lead-Scintillator (Pb/Sci) calorimeters.
∗1∗2∗3References
1) R. A. Khalek et al., arXiv:2103.05419.
2) A. Accardi et al., Eur. Phys. J. A 52, 268 (2016).
3) ALICE collaboration, ALICE-PUBLIC-2019-005, (2019)https://cds.cern.ch/record/2696471 .
4) S. Agostinelli et al., Nucl. Instrum. Methods Phys. Res.
A 506, 250 (2003).

RIKEN Nishina Center
Japan Society for the Promotion of Science
Department of Physics, Kobe University- 47 -1