Ⅱ-4. Hadron Physics

RIKEN Accel. Prog. Rep. 56 (2023)
RIKEN
Accel. Prog. Rep. 56 (2023)

Zero degree calorimeter for the ePIC experiment
S. Shimizu∗1,∗2 for the EIC Japan group
The Electron Ion Collider (EIC) is the next collider
scheduled to be built at the Brookhaven National Laboratory in US. It collides electrons and protons or nuclei and will provide a powerful measure to examine
the structure of protons and nuclei. In 2022, a newcollaboration was formed, named ePIC, as an experiment at the interaction point IP6. The ePIC detector
will be a multi-purpose detector, with suites of detectors in the far-forward and far-backward regions of theion-beam direction.
The Zero Degree Calorimeter (ZDC) is one of thefar-forward detector systems. It is used to detect photons and neutrons coming from the interaction point.
The ZDC enables measurements for several key EIC
physics programs1) such as exclusive vector meson production in e + A collisions or spectator-neutron-taggede + d deep inelastic scattering. Its ﬁrst design wasconsidered for EIC in the previous report.2) It comprises a crystal calorimeter and three types of sampling
calorimeters.
The same ZDC design was adopted to the ePIC detector as a baseline ePIC ZDC design. In the ePICcollaboration, a new software framework was developed and the ZDC design was migrated there. Figure 1
shows a schematic of the ePIC detector including theZDC.
A few details of the ZDC design are examined anddiscussed: material of the crystal calorimeter, radiation resistance of photon detectors, and placement ofthe ZDC.
The material of the crystal calorimeter was studied
by simulation. Two materials were compared: LYSOand PbWO4 , where the former has a >100 times higher
light yield but is more expensive with respect to thelatter. Considering the photon counting eﬀect, thecomparison showed no large diﬀerence in the cluster
ﬁnding eﬃciency. Worse energy resolution was observed for PbWO4 , but it is still acceptable for thephysics requirement of 20%. As far as the performanceof the calorimeter system is sustained as designed,
PbWO4 can be used for the ZDC crystal calorimeter.
The crystal calorimeter requires photon detectors
to detect light in the crystal, and avalanche photodiodes (APDs) are the ﬁrst candidate for the ZDC.
Hamamatsu APDs S8664-55 were irradiated at RANS,RIKEN Accelerator-driven compact Neutron Sources,
to test their radiation resistance. Following two daysof irradiation, the estimated dose on the APDs is 1012 –1013 neutrons/cm2 .a) All the irradiated APDs seem to∗1∗2a)Fig. 1. A schematic of the ePIC detector, observed from thedownstream of the ion beam line, as implemented in theePIC software framework. The ion beam goes from theleft side top to the right side bottom as indicated by thearrow. The large disks are calorimeter endcaps of theePIC main detector. The ZDC is the set of rectangularsolids at the bottom right. In the far-forward region,
only the ion beam line is shown.

lose their function. With the EIC operation for a thirdof a year, the EIC ZDC is expected to be exposed to8 × 1012 neq /cm2 per year.3) The APDs do not have
suﬃcient radiation resistance for the EIC ZDC and another technology is needed.
The ePIC ZDC will be situated between the electron
and ion beam lines. Its placement was revised following consultations with experts in US. The ZDC has
a limited space to place the front-end system close tothe ZDC. Discussion on the readout system has startedand is ongoing.
In summary, the previously reported ZDC design isadopted to the ePIC detector and discussions on several aspects is ongoing for realization of the design.
The ZDC eﬀort is also in close contact with the ALICE
FoCal development,4) which had several test-beam experiments conducted in 2022, as the same techniquewill be used in ZDC sampling calorimeters.
References
1) R. A. Khalek et al., EIC Yellow Report, arXiv:2103.05419.
2) S. Shimizu et al., RIKEN Accel. Prog. Rep. 55, 47(2022).
3) V. Baturin, internal document.
4) ALICE collaboration,
ALICE-PUBLIC-2019-005,
https://cds.cern.ch/record/2696471 .

RIKEN Nishina Center
Wako Nuclear Science Center (WNSC), IPNS, KEK
The dose estimation is based on the measurement using radioactivation of indium foils.

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