[Paper Review] Baikal-GVD: status and prospects

GVD Collaboration, А. В. Аврорин+50 more|arXiv (Cornell University)|Aug 30, 2018

Astrophysics and Cosmic Phenomena4 citations

TL;DR

Baikal-GVD is a km³-scale neutrino telescope under construction in Lake Baikal, using 288 optical modules per cluster to detect high-energy astrophysical neutrinos via Cherenkov radiation. By 2018, three clusters (864 OMs) were operational, enabling early detection of upward muons and high-energy cascade events, with upper limits on neutrino fluence derived from non-detection in coincidence with GW170817.

ABSTRACT

Baikal-GVD is a next generation, kilometer-scale neutrino telescope under construction in Lake Baikal. It is designed to detect astrophysical neutrino fluxes at energies from a few TeV up to 100 PeV. GVD is formed by multi-megaton subarrays (clusters). The array construction started in 2015 by deployment of a reduced-size demonstration cluster named "Dubna". The first cluster in its baseline configuration was deployed in 2016, the second in 2017 and the third in 2018. The full scale GVD will be an array of ~10000 light sensors with an instrumented volume of about 2 cubic km. The first phase (GVD-1) is planned to be completed by 2020-2021. It will comprise 8 clusters with 2304 light sensors in total. We describe the design of Baikal-GVD and present selected results obtained in 2015-2017.

Motivation & Objective

• To construct a kilometer-scale neutrino telescope in Lake Baikal to detect high-energy astrophysical neutrinos.
• To deploy a modular array of optical modules (OMs) on vertical strings to form clusters with high detection sensitivity.
• To enable early physics studies using partial deployments, including muon and cascade event detection.
• To search for neutrino coincidences with gravitational wave events such as GW170817.
• To establish a multi-megaton-scale detector with high angular and energy resolution for cosmic neutrino studies.

Proposed method

• Deploying optical modules (OMs) with photomultiplier tubes (PMTs) on vertical strings anchored to the lake floor at depths from 735 to 1260 m.
• Using 15 m spacing between OMs along each string, with 12 OMs grouped into functional detection units (DUs) per string.
• Implementing real-time data acquisition (DAQ) with trigger conditions based on minimum fired PMTs to filter signals.
• Connecting each cluster to shore via electro-optical cables for power, control, and high-bandwidth data transmission.
• Applying directional and energy reconstruction algorithms to identify neutrino candidates from Cherenkov light patterns.
• Using time- and space-coincidence cuts with gravitational wave triggers (e.g., GW170817) to suppress atmospheric background.

Experimental results

Research questions

• RQ1 Can Baikal-GVD detect high-energy astrophysical neutrinos using early-stage cluster deployments?
• RQ2 What is the sensitivity of Baikal-GVD to neutrinos associated with gravitational wave events like GW170817?
• RQ3 How effective are the detection and reconstruction techniques for upward-moving muon neutrinos and cascade events?
• RQ4 What upper limits can be placed on neutrino fluence from GW170817 using Baikal-GVD data?
• RQ5 To what extent can the modular design enable physics studies before full-scale deployment?

Key findings

• By April 2018, Baikal-GVD had deployed three clusters with 864 optical modules, making it the largest underwater neutrino telescope at that time.
• The first cluster (deployed April 2016) enabled the identification of upward through-going muons as clear neutrino candidates.
• Two high-energy cascade events were identified as potential astrophysical neutrino candidates using relaxed selection cuts.
• No significant neutrino candidates were found in coincidence with GW170817 within ±500 s or 14-day time windows.
• The median angular error for surviving events was 4.5°, with an expected atmospheric background of ~0.05 events during the ±500 s window.
• Upper limits on the neutrino spectral fluence were derived at 90% confidence level for both the ±500 s and 14-day time windows, consistent with theoretical models.