The optical module of Baikal-GVD

In April 2015, the first cluster of Baikal-GVD was deployed in Lake Baikal and put into operation. It comprises eight strings. Each string consists of 24 optical modules. An optical module is a detection element of Baikal-GVD; it includes a Hamamatsu R7081-100 photomultiplier tube with a high quantum sensitivity. We describe the design of the optical module, the front-end electronics, and the laboratory characterization and calibration.     

Data acquisition system for the Baikal-GVD neutrino telescope

The objective of the Baikal-GVD project is the construction of a km³-scale neutrino telescope in Lake Baikal. The Gigaton Volume Detector consists of a large three-dimensional array of photo-multiplier tubes. The first GVD-cluster has been deployed and commissioned in April 2015. The data acquisition system (DAQ) of the detector takes care of the digitization of the photo-multiplier tube signals, data transmission, filtering and storage. The design and the implementation of the data acquisition system are described.     

Exchange interaction at the supramolecular level. EPR investigation of two copper (II) compounds: [Cu2(acac)2(phen)2(bpe)](CIO4)2·(bpe)·CH3CN·H2O and [Cu2(acac)2(phen)2(bpp)](CIO4)2·6H2O (bpe=trans-1,2-bis(4-pyridyl)ethylene, bpp=bis(4-pyridyl)propane)

Intra- and intermolecular exchange and dipole-dipole interactions in two supramolecular compounds [Cu₂(acac)₂(phen)₂(bpe)](CIO₄)₂·(bpe)·CH₃CN·H₂O (I) and [Cu₂(acac)₂(phen)₂(bpp)]× (CIO₄)₂·6H₂O (II), which are built up of binuclear fragments through π-π stacking interactions, are investigated. The electron paramagnetic resonance (EPR) spectra of the polycrystalline samples of I and II were measured in the X-band in the temperature range of 300–4.2 K, and in the Q-band atT=300 and 4.2 K. The EPR spectra were interpreted as being due to weakly interacting dimer fragments. Triplet and singlet states of dimer fragments arise from a larger interactionJS ₁ S ₂ between two nearest copper complexes of two neighboring binuclear fragments. The theoretical analysis of the EPR spectrum of the polycrystalline sample for weakly interacting triplet states is carried out. The influence of the weak interaction between triplet states with value ofJ′ is considered in the model of the frequency exchange. A special attention is focused on the presence of the additional signal due to the exchange merging in some orientations where theJ′ value exceeds the fine structure parameters of the spectrum. The analysis of the conditions for the detection of the additional signal and of the influence of this signal on the form of the EPR spectrum allows us to estimate the value of the exchange interactionJ′=o.025±0.005 cm^?1 for compounds I and II and anisotropic part of exchange interaction between two nearest copper complexes asJ _zz =?0.02 cm^?1,J _xx.yy =0.01 cm^?1 for compound I.     

Copper(II) Cyanoacetate Polymer: Synthesis and Structure

A new copper carboxylate polymer with cyanoacetate anion as a ligand was synthesized and studied using X-ray diffraction, IR, and EPR spectroscopy. The crystal is tetragonal: a= 14.702(2) Å, c= 13.470(3) Å, Z= 8, space group I4₁/a, and R= 0.0634. The copper atoms in the centrosymmetric dimeric fragment have a square-pyramidal surrounding with the CuO₄N coordination core and are joined through four bidentate bridging anions of cyanoacetic acid Cu(1)"–O(1A) 1.931(4) Å, Cu(1)"–O(1B) 1.926(4) Å, Cu(1)–O(2B) 2.018(3) Å, Cu(1)–O(2A) 2.036(4) Å, and Cu(1)–N(1A)" 2.206(5) Å). The Cu···Cu" distance in the dimer is 2.709 Å. The copper atom is extended from the mean equatorial plane toward the axial nitrogen atom by 0.23 Å. EPR data confirm strong antiferromagnetic interaction (2J –275 cm^–1) between the copper(II) ions of the dimeric fragment, whereas the interaction between the dimers is significantly weaker (J< 0.3 cm^–1).     

Neutrino signal at Baikal from dark matter in the Galactic Center

We discuss neutrinos originating from dark matter in the Galactic Center and present sensitivity of Baikal Gigaton Volume Detector to this signal.     

Search for High-Energy Neutrinos from GW170817 with the Baikal-GVD Neutrino Telescope

JETP Letters - The Advanced Laser Interferometer Gravitational-Wave Observatory and Advanced Virgo observatories recently discovered gravitational waves from a binary neutron star inspiral. A short...     

Synthesis and spectral-luminescence properties of some substituted 1,3-diarylbenzo[f]quinolines

Amino derivatives of 1,3-diarylbenzo[f]quinoline were synthesized and subjected to reaction with methyl vinyl ketone in the presence of catalytic amounts of concentrated HCl to give the corresponding (3-oxobutyl) aminophenyl derivatives. The electronic absorption and fluorescence spectra were studied, and the absolute fluorescence quantum yields of the synthesized compounds were determined. A relationship between the position and intensity of the absorption bands and the electron-donor substituents was uncovered, and a substantial effect of the nature of the solvent on the fluorescent spectra was established.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 116–120, January, 1976.     

Dark matter constraints from an observation of dSphs and the LMC with the Baikal NT200

We have analyzed the neutrino events recoded in the deep-water neutrino experiment NT200 in Lake Baikal in five years of observations toward dark dwarf spheroidal galaxies (dSphs) in the southern hemisphere and the Large Magellanic Cloud (LMC). This analysis completes the series of works based on NT200 data in the search for a dark matter annihilation signal in astrophysical objects. We have found no significant excess in the number of observed events relative to the expected background from atmospheric neutrinos in all tested directions, in 22 dSphs and the LMC. For a sample of five selected dwarf galaxies we have performed a joint analysis of the data by the maximum likelihood method. We have obtained a correspondence of the observational data to the null hypothesis about the presence of only background events and established 90% confidence-level upper limits for the annihilation cross sections of dark matter particles with a mass from 30 GeV to 10 TeV in several annihilation channels both in the joint analysis of the selected sample of galaxies and in the analysis toward the LMC. The strongest constraints at a level of 7 × 10^–21 cm³ s^–1 have been obtained for the direction toward the LMC in the channel of annihilation into a pair of neutrinos.     

TUNKA-133: A new array for the study of ultra-high energy cosmic rays

A new array for studying ultra-high energy cosmic rays was inaugurated in 2009 in the Tunka Valley, about 50 km from Lake Baikal. Having an area of 1 km², the new facility allows us to study cosmic rays with energies of 10¹⁵–10¹⁸ eV via the a unified method for registering Cherenkov radiation from extensive air showers (EASes) and is making a substantial contribution to understanding the origin of ultra-high energy cosmic rays. We describe the current state of the experiment, the new methodological approach, our initial results, and the plans for further development of the array.