Baikal-HUNT is a joint Russian‑Chinese project to build a giant neutrino telescope in Lake Baikal. Its goal is to detect ultra‑high‑energy neutrinos (from 100 teraelectronvolts and above). The facility could become the largest in the world — it will occupy a volume of up to 30 cubic kilometers.
On November 2, representatives of the Institute of High Energy Physics of the Chinese Academy of Sciences arrived at MEPhI – senior researcher Xiohou Yu and postdoc Daniil Trofimov. They brought two deep‑sea optical modules that need to be calibrated.
“We came to MEPhI because it has a unique NEVOD facility, and we need its capabilities for our Baikal‑HUNT experiment,” said Xiohou Yu. – "Currently, we are working with JINR in Dubna and INP in Moscow, and we are already conducting joint experiments with them. This year, the Institute of High Energy Physics of the Chinese Academy of Sciences, together with JINR and INP, submitted an application for the HUNT project, and we hope to receive funding, which is expected to be gradual and jointly provided by Russia and China over a period of five years".
The HUNT project is being developed as a logical continuation of the Russian Baikal-GVD neutrino telescope. In total, about 2,300 deep‑sea strings and 50,000 optical modules will be manufactured for deployment in Lake Baikal. The experiment began in 2025, when two prototypes of the HUNT neutrino telescope strings were installed near the clusters of the Baikal-GVD neutrino telescope. Currently, three strings with 24 HUNT modules are already operational in the water. In the future, the information obtained from the HUNT neutrino telescope will be processed in a data center that is planned to be built in the city of Baikalsk on the southern shore of Lake Baikal. Both Russian and Chinese scientists will have access to the data center.
The chief researcher at the Scientific and Educational Center NEVOD (Neutrino Water Detector), Professor Anatoly Petrukhin from MEPhI, commented on the start of the cooperation as follows: “Recently, we conducted a successful test of a module from the Baikal-GVD experiment at NEVOD. Chinese scientists need to compare the data from their HUNT module and the data from the Baikal-GVD modules. To do this, the modules need to be calibrated under the same conditions — in Cherenkov radiation — and the only place on the planet where this can be done is our NEVOD.”
How the calibration process will proceed is explained by Semyon Khokhlov, an associate professor at the NEVOD REC: “The HUNT module will be placed in the center of the NEVOD pool. There is a coordinate‑track detector called DECOR around the pool, which can select horizontal muons with very high precision and reconstruct their tracks. The “selected” muons will generate Cherenkov light, and we will know the exact angle at which the Cherenkov light hits the module being tested. Every week, we will rotate the module under test by 15°, and it will be illuminated by Cherenkov radiation from different sides. The two Chinese modules brought to MEPhI will be calibrated in this way within 6–7 months. Then, when reconstructing events in the HUNT telescope, the dependencies measured for these two optical modules will be used for all 50,000 modules. The general idea of such calibration was patented by us six years ago”.
Why is module calibration necessary at all? The main problem with modern facilities for high‑energy astrophysics is the significant discrepancy in the results. The neutrino fluxes measured by the Baikal‑GVD and IceCube telescopes differ by several tens of percent. No one yet understands whether this is due to different neutrino fluxes from different parts of the galaxy or something else entirely. There is no mutual calibration; each experiment tests its equipment in a slightly different way. Therefore, it is very important to bring both the neutrino telescopes that have already been built and those that are currently under construction to a common standard. The nuclear university began to consider this problem several years ago, and in 2020, it patented a special method for calibrating optical modules using Cherenkov light from near‑horizontal muons. The Baikal‑GVD modules have already undergone this calibration at MEPhI, and now the calibration of Baikal‑HUNT has begun. Thus, the National Research Nuclear University MEPhI is becoming the world's most important center for testing equipment for neutrino astrophysics.
