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Deployment of the deep-sea neutrino telescope Baikal-GVD continues in Lake Baikal. By April 2022, ten telescope clusters, which include 2880 optical modules, were put into operation. One of the urgent tasks of the Baikal project is to study the possibility of increasing the detection efficiency of the detector based on the experience of its operation and the results obtained with other neutrino telescopes in recent years. In this paper, the authors consider a variant of optimizing the telescope configuration by installing an additional string of optical modules between the detector clusters (external string). An experimental version of the external garland was installed in Lake Baikal in April 2022. The paper presents the results from calculations of the efficiency of registration of neutrino events for a new setup configuration, the technical implementation of the system for recording and collecting data from the external garland, and the first results of its full-scale tests in Lake Baikal. [ABSTRACT FROM AUTHOR]

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 cm s have been obtained for the direction toward the LMC in the channel of annihilation into a pair of neutrinos. [ABSTRACT FROM AUTHOR]

We analyze sensitivity of the gigaton volume telescope Baikal-GVD for detection of neutrino signal from dark matter annihilations or decays in the Galactic Center. Expected bounds on dark matter annihilation cross section and its lifetime are found for several annihilation/decay channels. [ABSTRACT FROM AUTHOR]

The NT1000 deep-water neutrino telescope with an effective volume of ∼2 km is currently being developed at Lake Baikal by the BAIKAL collaboration. The telescope will be composed of functionally independent setups-clusters of strings of optical modules based on photomultiplier tubes (with eight strings in each cluster). Since 2011, field tests of the basic elements and systems of the future telescope included in autonomous measuring complexes-prototypes of the NT1000 cluster-have been performed at Lake Baikal. The basic elements and the layout of one of the currently considered versions of the acoustic positioning system for the NT1000 telescope are described, and results of tests of the system prototype included as a component in the experimental cluster of the year 2012 are presented. [ABSTRACT FROM AUTHOR]

We present the results of our search for neutrino events coinciding in time and direction with gamma-ray bursts (GRBs) with the Baikal underwater neutrino telescope NT200. No events confirming a neutrino accompaniment of GRBs have been detected. Model-independent limits (Greens function) on the neutrino flux from GRBs have been obtained. For the Waxman-Bahcall neutrino spectrum, the limit on the neutrino flux from a GRB has been found to be EΦ ⩽ 1.1 × 10 GeV cm s sr. [ABSTRACT FROM AUTHOR]

A project of the NT1000 deep-water neutrino telescope with an effective volume of ∼1 km is currently being developed by the BAIKAL collaboration. The telescope will be located in Lake Baikal in close vicinity of the NT200+ detector, which is currently in operation. The telescope will be composed of 12 clusters with 8 similar strings of optical modules in each (each string has two sections of the NT1000 optical modules). The section of the NT1000 optical modules has been developed using higher-efficiency photomultiplier tubes and state-of-the-art electronics. The field tests of the experimental string consisting of two sections with six optical modules in each have been performed. The results of these investigations are used in the project of the NT1000 neutrino telescope and in the hydrological study of Lake Baikal. [ABSTRACT FROM AUTHOR]

The history, current status, and prospects for the development of the Baikal Neutrino Project are considered. The main physical results obtained with the help of NT200 and NT200+ neutrino telescopes are presented. [ABSTRACT FROM AUTHOR]

We review the present status of the Baikal Neutrino Experiment and present results of a search for upward-going atmospheric neutrinos and magnetic monopoles obtained with the detector NT200. The results of a search for very high energy neutrinos are presented and an upper limit on the extraterrestrial diffuse neutrino flux is obtained. We describe the strategy of upgrading the NT200 to NT200+ and creating a detector on the Gigaton scale at Lake Baikal. The first results obtained with the new NT200+ detector as a basic cell of a future Gigaton detector are presented. [ABSTRACT FROM AUTHOR]

High-frequency noise of Lake Baikal is investigated using a submersible self-contained instrument to determine the noise background for the acoustic detection of superhigh-energy neutrinos. It is found that, under stationary and uniform meteorological conditions, the integral noise power in the frequency band 1–50 kHz is virtually independent of depth and is 10–200 mPa or more, depending on the specific conditions. The noise itself contains multiple short pulses of different amplitudes and shapes. [ABSTRACT FROM AUTHOR]

New results from the Baikal neutrino telescope NT200, based on the first 5 years of operation (1998–2003), are presented. We derive an all-flavor limit on the diffuse flux of astrophysical neutrinos between 20 TeV and 50 PeV, extract an enlarged sample of high energy muon neutrino events, and obtain limits on the flux of high energy atmospheric muons. In 2005, the upgraded telescope NT200+ will be commissioned: 3 additional distant strings with only 12 photo-multipliers each will rise the effective volume to 20 Mton at 10 PeV for this largest running neutrino telescope in the Northern hemisphere. [ABSTRACT FROM AUTHOR]

The hydroacoustic coordinate-measuring system of the NT-200 Baikal neutrino telescope is described. It is a ranging long-base hydroacoustic system constantly operating in an automated or interactive mode and capable of measuring the coordinates of the detecting modules of the NT-200 to within 20 cm. Special attention is given to the justification of the estimate of the coordinate measurement errors. As an illustration, some results of measuring the coordinates of the elements of the NT-200 and the hydrophysical characteristics of lake Baikal are presented. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

Abstract: The operation of large underwater neutrino telescopes requires the precise knowledge of the water parameters governing light absorption and scattering, as well as a continuous monitoring of these parameters. For this purpose, a stationary underwater device, ASP-15, has been developed by the Baikal collaboration. We describe the basic assumptions and formulae behind ASP-15, the methods how absorption length, scattering length and phase functions are determined, the design of the device, and give some results obtained over many years of operation in conjuction with the Baikal telescope NT200. [Copyright &y& Elsevier]

Abstract: The Neutrino Telescope NT200 is operated since 1998 and was upgraded to the 10 Mton detector NT200+ in 2005. The preparation towards a km3-scale (Gigaton Volume) detector in Lake Baikal is currently a central activity. As an important milestone, a km3-prototype string, based on completely new technology, has been installed and was operating together with NT200+ since April 2008. Also selected astroparticle physics results from the long-term operation of NT200 are presented. [Copyright &y& Elsevier]

Abstract: The first stage Baikal Neutrino Telescope NT200 has been operating since 1998 and was upgraded to the 10Mton detector NT200+ in 2005. The preparation towards a development of a km3-scale detector in Lake Baikal is currently a central activity point. As an important milestone a km3-prototype Cherenkov string, based on completely new technology, was installed in 2008 and has been successfully operating together with NT200+. It was upgraded in April 2009. Also, we review the status of high-energy acoustic neutrino detection activities in Lake Baikal. [ABSTRACT FROM AUTHOR]

Abstract: The 10Mton scale Neutrino telescope is operating in Lake Baikal since April, 2005. It''s main physics goal is the detection of high energy neutrino cascades in the – energy range. The sensitivity to astrophysical diffuse neutrinos is four times that of it''s predecessor NT200 the telescope that has been operating since 1998, yielding a variety of physics results. A km-scale (Gigaton Volume) Neutrino telescope in Lake Baikal is planned, the R&D phase has started in 2006. We give the basic layout of this Baikal km3-detector, which will be made of building blocks similar to . [Copyright &y& Elsevier]

Abstract: We present the results of a search for high-energy extraterrestrial neutrinos with the Baikal underwater Cherenkov detector NT200, based on data taken in 1998–2003. Upper limits on the diffuse fluxes of ν e + ν μ + ν τ , predicted by several models of AGN-like neutrino sources, are derived. For an E −2 behavior of the neutrino spectrum, our limit is E 2 Φ ν (E)<8.1×10−7 cm−2 s−1 sr−1 GeV over an neutrino energy range 2×104–5×107 GeV. The upper limit on the resonant diffuse flux is . [Copyright &y& Elsevier]

Measurements of optical properties in media enclosing Cherenkov neutrino telescopes are important not only at the moment of the selection of an adequate site, but also for the continuous characterization of the medium as a function of time. Over the two last decades, the Baikal collaboration has been measuring the optical properties of the deep water in Lake Baikal (Siberia) where, since April 1998, the neutrino telescope NT-200 is in operation. Measurements have been made with custom devices. The NEMO Collaboration, aiming at the construction of a km3 Cherenkov neutrino detector in the Mediterranean Sea, has developed an experimental setup for the measurement of oceanographic and optical properties of deep sea water. This setup is based on a commercial transmissometer. During a joint campaign of the two collaborations in March and April 2001, light absorption, scattering and attenuation in water have been measured. The results are compatible with previous ones reported by the Baikal Collaboration and show convincing agreement between the two experimental techniques. [Copyright &y& Elsevier]