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Register a new userMeasuring muon tracks in Baikal-GVD using a fast reconstruction algorithm
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The Baikal Gigaton Volume Detector (Baikal-GVD) is a km$^3$-scale neutrino detector currently under construction in Lake Baikal, Russia. The detector consists of several thousand optical sensors arranged on vertical strings, with 36 sensors per string. The strings are grouped into clusters of 8 strings each. Each cluster can operate as a stand-alone neutrino detector. The detector layout is optimized for the measurement of astrophysical neutrinos with energies of $sim$ 100 TeV and above. Events resulting from charged current interactions of muon (anti-)neutrinos will have a track-like topology in Baikal-GVD. A fast $chi^2$-based reconstruction algorithm has been developed to reconstruct such track-like events. The algorithm has been applied to data collected in 2019 from the first five operational clusters of Baikal-GVD, resulting in observations of both downgoing atmospheric muons and upgoing atmospheric neutrinos. This serves as an important milestone towards experimental validation of the Baikal-GVD design. This analysis is limited to single-cluster data, favoring nearly-vertical tracks.
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The Baikal-GVD is a large scale neutrino telescope being constructed in Lake Baikal. The majority of signal detected by the telescope are noise hits, caused primarily by the luminescence of the Baikal water. Separating noise hits from the hits produced by Cherenkov light emitted from the muon track is a challenging part of the muon event reconstruction. We present an algorithm that utilizes a known directional hit causality criterion to contruct a graph of hits and then use a clique-based technique to select the subset of signal hits.The algorithm was tested on realistic detector Monte-Carlo simulation for a wide range of muon energies and has proved to select a pure sample of PMT hits from Cherenkov photons while retaining above 90% of original signal.
Baikal-GVD is a km$^3$-scale neutrino telescope being constructed in Lake Baikal. Muon and partially tau (anti)neutrino interactions near the detector through the W$^{pm}$-boson exchange are accompanied by muon tracks. Reconstructed direction of the track is arguably the most precise probe of the neutrino direction attainable in Cerenkov neutrino telescopes. Muon reconstruction techniques adopted by Baikal-GVD are discussed in the present report. Performance of the muon reconstruction is studied using realistic Monte Carlo simulation of the detector. The algorithms are applied to real data from Baikal-GVD and the results are compared with simulations. The performance of the neutrino selection based on a boosted decision tree classifier is discussed.
The Baikal-GVD (Gigaton Volume Detector) is a km$^{3}$- scale neutrino telescope located in Lake Baikal. Currently (year 2021) the Baikal-GVD is composed of 2304 optical modules divided to 8 independent detection units, called clusters. Specific neutrino interactions can cause Cherenkov light topology, referred to as a cascade. However, cascade-like events originate from discrete stochastic energy losses along muon tracks. These cascades produce the most abundant background in searching for high-energy neutrino cascade events. Several methods have been developed, optimized, and tested to suppress background cascades.
In April 2019, the Baikal-GVD collaboration finished the installation of the fourth and fifth clusters of the neutrino telescope Baikal-GVD. Momentarily, 1440 Optical Modules (OM) are installed in the largest and deepest freshwater lake in the world, Lake Baikal, instrumenting 0.25 cubic km of sensitive volume. The Baikal-GVD is thus the largest neutrino telescope on the Northern Hemisphere. The first phase of the detector construction is going to be finished in 2021 with 9 clusters, 2592 OMs in total, however the already installed clusters are stand-alone units which are independently operational and taking data from their commissioning. Huge number of channels as well as strict requirements for the precision of the time and charge calibration (ns, p.e.) make calibration procedures vital and very complex tasks. The inter cluster time calibration is performed with numerous calibration systems. The charge calibration is carried out with a Single Photo-Electron peak. The various data acquired during the last three years in regular and special calibration runs validate successful performance of the calibration systems and of the developed calibration techniques. The precision of the charge calibration has been improved and the time dependence of the obtained calibration parameters have been cross-checked. The multiple calibration sources verified a 1.5 - 2.0 ns precision of the in-situ time calibrations. The time walk effect has been studied in detail with in situ specialized calibration runs.
The Baikal-GVD neutrino telescope currently consists of 8 clusters of 288 optical modules (photodetectors). One cluster comprises 8 strings, each of which is subdivided into 3 sections of 12 optical modules. This paper presents the methods of time synchronization between the different GVD components (optical modules, sections, clusters) and estimations of time synchronization accuracy.
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