At present, the international experiment T2K, in which DLNP specialists participate, is upgrading the near detector ND280. In the future, the detector will become a constituent of the new Hyper-Kamiokande project.


Preparing the assembly of the active target SFGD | Credits: archive of JINR group

The most significant part of the upgraded detector ND280 is the active target SFGD made of almost two million scintillation cubes measuring 1x1x1 cm3. Each cube is pierced with three holes for wavelength shifting fibres which will transmit light from the detector to photodetectors. All the cubes have been manufactured by the UNIPLAST company (Vladimir) for over two years. Specialists from INR of RAS (Troitsk) took the main responsibility by controlling the produced SFGD elements. Our INR colleagues controlled the quality of cubes, checked their geometrics, and DLNP specialists tested optical parameters of cubes on test benches of the Laboratory. 


Starting the assembly of the active target SFGD | Credits: archive of JINR group

Earlier, a platform for assembling the SFGD target and a system to reach the detector from above were developed and manufactured by DLNP specialists (see “Assembly Equipment for the T2K Near Detector Active Target Completed”). Using nylon threads, the cube array was assembled in 56 layers each of 192x184 cubes. In summer 2022, both the cube array and the platform with the system to reach the detector from above were transported to the accelerator complex J-PARC (Japan).


The target before mounting the other box walls | Credits: archive of JINR group

Late October, the assembly of the SFGD detector was launched there. Its box was specially developed and produced at CERN. It was decided that the detector would be assembled using nylon threads inserted into the layers. The cube array was assembled with the help of the platform and the system to reach the detector from above, which ensured the successful fulfilment of work.


Before the final stage of the target assembly | Credits: archive of JINR group

Representatives from JINR, INR, KEK (High-Energy Accelerator Research Organization in Japan), Imperial College London, the University of Oxford, Stony Brook University in New York were involved in the cube array assembly. In October−December 2022, A. V. Shaykovsky, A. O. Kolesnikov and I. I. Vasilyev participated in the detector assembly. Thanks to concerted efforts and well-coordinated activities of all participants, the detector assembly in the box was successfully completed, and on December 27, the T2K collaboration got this good news as a New Year’s present. All the layers of the cube array were assembled, the walls of the box and the top cover fixed. This stage of upgrading the near detector ND280 and preparing it for operation was finished.


The closed box with the SFGD target assembled | Credits: archive of JINR group

The next serious task for the collaboration will be to change nylon threads for wavelength shifting optical fibres. This activity will start in the J-PARC complex already in January 2023, and DLNP specialists will be also involved in it.

Yury Davydov,
Head of the DLNP Experimental Department of Multiple Hadronic Processes