G. Safronov

We report on the first observation of the diffuse cosmic neutrino flux with the Baikal-GVD neutrino telescope. Using cascade-like events collected by Baikal-GVD in 2018--2021, a significant excess of events over the expected atmospheric background is observed. This excess is consistent with the high-energy diffuse cosmic neutrino flux observed by IceCube. The null cosmic flux assumption is rejected with a significance of 3.05$\sigma$. Assuming a single power law model of the astrophysical neutrino flux with identical contribution from each neutrino flavor, the following best-fit parameter values are found: the spectral index $\gamma_{astro}$ = $2.58^{+0.27}_{-0.33}$ and the flux normalization $\phi_{astro}$ = 3.04$^{+1.52}_{-1.21}$ per one flavor at 100 TeV.

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 it’s baseline configuration was deployed in 2016, the second in 2017 and the third in 2018. The full-scale GVD will be an array of ~10.000 light sensors with an instrumented volume about of 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.

Abstract The Baikal Gigaton Volume Detector (Baikal-GVD) is a km $$^3$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow /> <mml:mn>3</mml:mn> </mml:msup> </mml:math> -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 $$\sim $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mo>∼</mml:mo> </mml:math> 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 $$\chi ^2$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mi>χ</mml:mi> <mml:mn>2</mml:mn> </mml:msup> </mml:math> -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. The analysis is limited to single-cluster data, favoring nearly-vertical tracks.

The progress in the construction and operation of the Baikal Gigaton Volume Detector in Lake Baikal is reported. The detector is designed for search for high energy neutrinos whose sources are not yet reliably identified. It currently includes over 2000 optical modules arranged on 64 strings, providing an effective volume of 0.4 km3 for cascades with energy above 100 TeV. We review the scientific case for Baikal-GVD, the construction plan, and first results from the partially built experiment, which is currently the largest neutrino telescope in the Northern Hemisphere and still growing up.

We present measurements of the reduction of light output by plastic scintillators irradiated in the CMS detector during the 8 TeV run of the Large Hadron Collider and show that they indicate a strong dose rate effect. The damage for a given dose is larger for lower dose rate exposures. The results agree with previous measurements of dose rate effects, but are stronger due to the very low dose rates probed. We show that the scaling with dose rate is consistent with that expected from diffusion effects.

The Advanced Laser Interferometer Gravitational-Wave Observatory and Advanced Virgo observatories recently discovered gravitational waves from a binary neutron star inspiral. A short gamma-ray burst that followed the merger of this binary was also recorded by Fermi gamma-ray burst monitor and International Gamma-Ray Astrophysics Laboratory, indicating particle acceleration by the source. The precise location of the event was determined by optical detections of emission following the merger. We searched for high-energy neutrinos from the merger in the energy range of 1 TeV–100 PeV using the Baikal Gigaton Volume Detector. No neutrinos directionally coincident with the source were detected within ±500 s around the merger time, as well as during a 14-day period after the gravitational wave detection. We derived 90% C.L. upper limits on the neutrino fluence from GW170817 during a ±500 s window centered on the gravitational wave trigger time, and a 14-day window following the gravitational wave signal under the assumption of an E−2 neutrino energy spectrum.

Baikal-GVD is a cubic-kilometer scale neutrino telescope, which is currently under construction in Lake Baikal. Baikal-GVD is an array of optical modules arranged in clusters. The first cluster of the array has been deployed and commissioned in April 2015. To date, Baikal-GVD consists of 3 clusters with 864 optical modules. One of the vital conditions for optimal energy, position and direction reconstruction of the detected particles is the time calibration of the detector. In this article, we describe calibration equipment and methods used in Baikal-GVD and demonstrate the accuracy of the calibration procedures.

Next generation cubic kilometer scale neutrino telescope Baikal-GVD is currently under construction in Lake Baikal. The detector is specially designed for search for high energies neutrinos whose sources are not yet reliably identified. Since April 2018 the telescope has been successfully operated in complex of three functionally independent clusters i.e. sub-arrays of optical modules (OMs) where now are hosted 864 OMs on 24 vertical strings. Each cluster is connected to shore by individual electro-optical cables. The effective volume of the detector for neutrino initiated cascades of relativistic particles with energy above 100 TeV has been increased up to about 0.15 km 3 . Preliminary results obtained with data recorded in 2016 and 2017 are discussed.

ABSTRACT The existence of high-energy astrophysical neutrinos has been unambiguously demonstrated, but their sources remain elusive. IceCube reported an association of a 290-TeV neutrino with a gamma-ray flare of TXS 0506 + 056, an active galactic nucleus with a compact radio jet pointing to us. Later, radio-bright blazars were shown to be associated with IceCube neutrino events with high statistical significance. These associations remained unconfirmed with the data of independent experiments. Here, we report on the detection of a rare neutrino event with the estimated energy of 224 ± 75 TeV from the direction of TXS 0506 + 056 by the new Baikal Gigaton Volume Detector (Baikal-GVD) in April 2021. This event is the highest energy cascade detected so far by the Baikal-GVD neutrino telescope from a direction below horizon. The result supports previous suggestions that radio blazars in general, and TXS 0506 + 056 in particular, are the sources of high-energy neutrinos, and opens up the cascade channel for the neutrino astronomy.

Currently in Lake Baikal a new-generation neutrino telescope is being deployed: Baikal-GVD, a deep underwater Cherenkov detector on the cubic-kilometer scale. This paper presents the status of the detector implementation and the first physical results obtained with the existing configuration.

Baikal-GVD is a next generation, kilometer-scale neutrino telescope currently under construction in Lake Baikal.GVD is formed by multi-megaton subarrays (clusters) and is designed for the detection of astrophysical neutrino fluxes at energies from a few TeV up to 100 PeV.The design of Baikal-GVD allows one to search for astrophysical neutrinos with flux values measured by IceCube already at early phases of the array construction.We present here preliminary results of the search for high-energy neutrinos via the cascade mode with the Baikal-GVD neutrino telescope.

Abstract Forward dijet production with wide rapidity separation in pp -collisions at LHC and Tevatron energies is discussed. Predictions on forward dijet ratios and azimuthal decorrelations from various GLAPD- and BFKL- Monte-Carlo event generators are presented.

A significant progress in the construction and operation of the Baikal Gigaton Volume Detector in Lake Baikal, the largest and deepest freshwater lake in the world, is reported.The effective volume of the detector for neutrino initiated cascades of relativistic particles with energy above 100 TeV has been increased up to about 0.25 km 3 .This unique scientific facility, the largest operating neutrino telescope in Northern Hemisphere, allows already to register two to three events per year from astrophysical neutrinos with energies exceeding 100 TeV.Preliminary results obtained with data recorded in 2016-2018 are announced.Multimessenger approach is used to relate finding of cosmic neutrinos with those of classical astronomers, with X-ray or gamma-ray observations and the gravitational wave events.

We present data on the luminescence of the Baikal water medium collected with the Baikal-GVD neutrino telescope.This three-dimensional array of light sensors allows the observation of time and spatial variations of the ambient light field.We report on observation of an increase of luminescence activity in 2016 and 2018.On the contrary, we observed practically constant optical noise in 2017.An agreement has been found between two independent optical noise data sets.These are data collected with online monitoring system and the trigger system of the cluster.

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 km3 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.

Multi-messenger astronomy is a powerful tool to study the physical processes driving the non-thermal Universe. A combination of observations in cosmic rays, neutrinos, photons of all wavelengths and gravitational waves is expected. The alert system of the Baikal-GVD detector under construction will allow for a fast, on-line reconstruction of neutrino events recorded by the Baikal-GVD telescope and - if predefined conditions are satisfied - for the formation of an alert message to other communities. The preliminary results of searches for high-energy neutrinos in coincidence with GW170817/GRB170817A using the cascade mode of neutrino detection are discussed. Two Baikal-GVD clusters were operating during 2017. The zenith angle of NGC 4993 at the detection time of the GW170817 was 93.3 degrees. No events spatially coincident with GRB170817A were found. Given the non-detection of neutrino events associated with GW170817, upper limits on the neutrino fluence were established.

Baikal-GVD neutrino telescope is under construction now. The 2021 telescope configuration includes 8 clusters of 288 photodetectors each. Сluster is a functionally complete detector that can register events, muons and cascade showers, in stand-alone mode and jointly with other clusters. The angular resolution of the detector is determined by the accuracy of the time measurement with the telescope channels. The uncertainty of the time measurement depends, in particular, on the accuracy of the time synchronization of the channels. The article describes the method of synchronization of Baikal-GVD and presents the results of studies of the accuracy of time synchronization both for individual clusters and for the installation as a whole.

Baikal-GVD is a cubic kilometer-scale neutrino telescope currently under construction in Lake Baikal. The detector’s components are mobile and may drift from their initial coordinates or change their spatial orientation. This introduces a reconstruction error, particularly a timing error for PMT hits. This problem is mitigated by a combination of a hydroacoustic positioning system and per-component acceleration and orientation sensors. Under regular conditions, the average positioning accuracy for a GVD component is estimated to be less than 13 cm.

Baikal-GVD is a neutrino telescope currently under construction in Lake Baikal.GVD is formed by multi-megaton subarrays (clusters).The design of Baikal-GVD allows one to search for astrophysical neutrinos already at early phases of the array construction.We present here preliminary results of a search for high-energy neutrinos with GVD in 2019-2020.

The PMTs of the CMS Hadron Forward calorimeter were found to generate a large size signal when their windows were traversed by energetic charged particles. This signal, which is due to Čerenkov light production at the PMT window, could interfere with the calorimeter signal and mislead the measurements. In order to find a viable solution to this problem, the response of four different types of PMTs to muons traversing their windows at different orientations is measured at the H2 beam-line at CERN. Certain kinds of PMTs with thinner windows show significantly lower response to direct muon incidence. For the four anode PMT, a simple and powerful algorithm to identify such events and recover the PMT signal using the signals of the quadrants without window hits is also presented. For the measurement of PMT responses to Čerenkov light, the Hadron Forward calorimeter signal was mimicked by two different setups in electron beams and the PMT performances were compared with each other. Superior performance of particular PMTs was observed.

Baikal-GVD is a cubic-kilometer scale deep-underwater neutrino detector being constructed in Lake Baikal.It is designed to detect neutrinos from ∼100 GeV to multi-PeV energies and beyond.Detector deployment began in Spring 2015.Since April 2020 the detector includes seven 8-string clusters carrying in total 2016 optical modules located at depths from 750 to 1275 meters.By the end of the first phase of detector construction in 2024 it is planned to deploy 15 clusters, reaching the effective volume for high-energy cascade detection of 0.75 km 3 .The design and status of the Baikal-GVD detector and first results of data analysis are presented in this report.

We present data on the Baikal water luminescence collected with the Baikal-GVD neutrino telescope. This three-dimensional array of photo-sensors allows the observation of time and spatial variations of the ambient light field. We report on annual increase of luminescence activity in years 2018-2020. We observed a unique event of a highly luminescent layer propagating upwards with a maximum speed of 28 m/day for the first time.

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.

A readout box prototype for the CMS Hadron Forward calorimeter upgrade was built and tested in the CERN H2 beamline. The prototype was designed to enable simultaneous tests of different readout options for the four anode upgrade PMTs, new front-end electronics design and new cabling. The response of the PMTs with different readout options was uniform and the background response was minimal. Multi-channel readout options further enhanced the background elimination. Passing all the electronic, mechanical and physics tests, the readout box proved to be capable of providing the forward hadron calorimeter operational requirements in the upgrade era.

A cubic kilometer scale neutrino telescope Baikal-GVD is currently under construction in Lake Baikal. Baikal-GVD is designed to detect Cerenkov radiation from products of astrophysical neutrino interactions with Baikal water by a lattice of photodetectors submerged between the depths of 1275 and 730 m. The detector components are mounted on flexible strings and can drift from their initial positions upwards to tens of meters. This introduces positioning uncertainty which translates into a timing error for Cerenkov signal registration. A spatial positioning system has been developed to resolve this issue. In this contribution, we present the status of this system, results of acoustic measurements and an estimate of positioning error for an individual component.

In April 2015, the first part (cluster) of the newly constructed next-generation neutrino telescope, Gigaton Volume Detector (GVD), was put into operation in the lake Baikal and started with data taking followed by another cluster installed in April 2017 thus doubling the number of installed Optical Modules (OMs) and instrumented volume. Moreover, the substantial extension of this detector is planned in the next few years. Specifically, another two clusters are going to be installed every consecutive year. In total 8 clusters consisting of 2304 OMs with overall effective volume ~0.4 km3 is going to be deployed by 2020. The vital condition for high angular resolution of reconstructed tracks of particles detected in GVD is a precise timing of individual channels which can be achieved with specialized time calibration systems. In this article, the different light sources and procedures used for time calibration of the GVD in the past as well as the newly developed ones are described and the results of the 2016 time calibration of the cluster Dubna are presented, especially the precision of intra and intersection calibrations and variations of calibration parameters in time.

The Baikal-GVD neutrino telescope is being constructed in Lake Baikal.The robust Baikal Analysis and Reconstruction Software (BARS) has been developed to convert raw data into physics results.To provide a stable and continuous analysis of all the data, an automatic data processing using a database is developed.The flexibility of the concept makes it easy to add new steps at any point of the analysis chain.The software is a ROOT-based collection of C++ classes driven by a central event loop.Now the basic algorithms have been implemented in the system such as event building, signal extraction, background rejection and simple reconstruction.

A significant progress in the construction and operation of the Baikal Gigaton Volume Detector in Lake Baikal, the largest and deepest freshwater lake in the world, is reported. The effective volume of the detector for neutrino initiated cascades of relativistic particles with energy above 100 TeV has been increased up to about 0.25 cubic kilometer. This unique scientific facility, the largest operating neutrino telescope in Northern Hemisphere, allows already to register two to three events per year from astrophysical neutrinos with energies exceeding 100 TeV. Preliminary results obtained with data recorded in 2016-2018 are announced. Multimessenger approach is used to relate finding of cosmic neutrinos with those of classical astronomers, with X-ray or gamma-ray observations and the gravitational wave events.

The Baikal-GVD deep underwater neutrino experiment participates in the international multi-messenger program on discovering the astrophysical sources of high energy fluxes of cosmic particles, while being at the stage of deployment with a gradual increase of its effective volume to the scale of a cubic kilometer. In April 2021 the effective volume of the detector has been reached 0.4 km$^3$ for cascade events with energy above 100 TeV generated by neutrino interactions in Lake Baikal. The alarm system in real-time monitoring of the celestial sphere was launched at the beginning of 2021, that allows to form the alerts of two ranks like “muon neutrino” and “VHE cascade”. Recent results of fast follow-up searches for coincidences of Baikal-GVD high energy cascades with ANTARES/TAToO high energy neutrino alerts and IceCube GCN messages will be presented, as well as preliminary results of searches for high energy neutrinos in coincidence with the magnetar SGR 1935+2154 activity in period of radio and gamma burst in 2020.

The Baikal Gigaton Volume Detector (Baikal-GVD) is a km$^3$-scale neutrino detector currently under construction in Lake Baikal, Russia. The detector currently consists of 2304 optical modules arranged on 64 vertical strings. Further extension of the array is planned for March 2022. The data from the partially complete array have been analyzed using a $\chi^2$-based track reconstruction algorithm. After suppression of the downward-going atmospheric muon background, a flux of upward-going neutrino events is observed, dominated by the atmospheric neutrinos. The observed flux is in good agreement with Monte Carlo predictions.

Reconstructed tracks of muons produced in neutrino interactions provide precise information about the neutrino direction.Therefore, track-like events are a powerful tool to search for neutrino pointlike sources.Recently, Baikal-GVD has demonstrated the first sample of low-energy neutrino candidate events extracted from the data of the season 2019 in a so-called single-cluster analysis -treating each cluster as an independent detector.In this paper, the extension of the tracklike event analysis to a wider data set is discussed and the first high-energy track-like events are demonstrated.The status of multi-cluster track reconstruction and that of the event analysis are also discussed.

We present a new procedure for time calibration of the Baikal-GVD neutrino telescope.The track reconstruction quality depends on accurate measurements of arrival times of Cherenkov photons.Therefore, it is crucial to achieve a high precision in time calibration.For that purpose, in addition to other calibration methods, we employ a new procedure using atmospheric muons reconstructed in a single-cluster mode.The method is based on iterative determination of effective time offsets for each optical module.This paper focuses on the results of the iterative reconstruction procedure with time offsets from the previous iteration and the verification of the method developed.The theoretical muon calibration precision is estimated to be around 1.5 -1.6 .

Monte Carlo event simulation with BFKL evolution is discussed. We report current status of a Monte Carlo event generator ULYSSES with BFKL evolution implemented. The ULYSSES, based on Pythia Monte Carlo generator, would help to reveal BFKL effects at LHC energies. In particular, such an observable as dijet K-factor can serve as a source of BFKL dynamics at the LHC, and it would also help to search for new physics.

Baikal-GVD is a next generation, kilometer-scale neutrino telescope currently under construction in Lake Baikal. GVD is formed by multi-megaton subarrays (clusters) and is designed for the detection of astrophysical neutrino fluxes at energies from a few TeV up to 100 PeV. The design of Baikal-GVD allows one to search for astrophysical neutrinos with flux values measured by IceCube already at early phases of the array construction. We present here preliminary results of the search for high-energy neutrinos via the cascade mode obtained in 2015 and 2016.

The quality of the incoming experimental data has a significant importance for both analysis and running the experiment.The main point of the Baikal-GVD DQM system is to monitor the status of the detector and obtained data on the run-by-run based analysis.It should be fast enough to be able to provide analysis results to detector shifter and for participation in the global multimessaging system.

Baikal-GVD is a kilometer scale neutrino telescope currently under construction in Lake Baikal. Due to water currents in Lake Baikal, individual photomultiplier housings are mobile and can drift away from their initial position. In order to accurately determine the coordinates of the photomultipliers, the telescope is equipped with an acoustic positioning system. The system consists of a network of acoustic modems, installed along the telescope strings and uses acoustic trilateration to determine the coordinates of individual modems. This contribution discusses the current state of the positioning in Baikal-GVD, including the recent upgrade to the acoustic modem polling algorithm.

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.

Lake Baikal in Siberia is one of the most interesting lakes in the world. It is the world’s largest reservoir of fresh surface water and home to several hundred endemic species. At the same time it harboured the first underwater neutrino telescope NT200, now followed by its successor Baikal-GVD, a cubic-kilometre scale neutrino telescope. Within the Baikal Neutrino project a number of methods and instruments have been designed to study various processes in the Baikal ecosystem. Hundreds of optical, acoustic and other sensors allow for long-term 3D monitoring of water parameters like temperature, inherent optical properties or the intensity of water luminescence, as well as processes like sedimentation or deep water renewal. Here we present selected results of the interdisciplinary environmental studies.

We present data on the luminescence of the Baikal water medium collected with the Baikal-GVD neutrino telescope. This three-dimensional array of light sensors allows the observation of time and spatial variations of the ambient light field. In 2016, we observed a maximum of luminescence activity between July and October.

Abstract The high-energy muon neutrino events of the IceCube telescope, that are triggered as neutrino alerts in one of two probability ranks of astrophysical origin, “gold” and “bronze”, have been followed up by the Baikal-GVD in a fast quasi-online mode since September 2020. Search for correlations between alerts and GVD events reconstructed in two modes, muon-track and cascades (electromagnetic or hadronic showers), for the time windows ±1 h and ±12 h does not indicate statistically significant excess of the measured events over the expected number of background events. Upper limits on the neutrino fluence will be presented for each alert.

Baikal-GVD is a gigaton-scale neutrino observatory under construction in Lake Baikal.It currently produces about 100 GB of data every day.For their automatic processing, the Baikal Analysis and Reconstruction software (BARS) was developed.At the moment, it includes such stages as hit extraction from PMT waveforms, assembling events from raw data, assigning timestamps to events, determining the position of the optical modules using an acoustic positioning system, data quality monitoring, muon track and cascade reconstruction, as well as the alert signal generation.These stages are implemented as C++ programs which are executed sequentially one after another and can be represented as a directed acyclic graph.The most resource-consuming programs run in parallel to speed up processing.A separate Python package based on the luigi package is responsible for program execution control.Additional information such as the program execution status and run metadata are saved into a central database and then displayed on the dashboard.Results can be obtained several hours after the run completion.

The Baikal-GVD is a neutrino telescope under construction in Lake Baikal. The main goal of the Baikal-GVD is to observe neutrinos via detecting the Cherenkov radiation of the secondary charged particles originating in the interactions of neutrinos. In 2021, the installation works concluded with 2304 optical modules installed in the lake resulting in effective volume approximately 0.4 km$^{3}$. In this paper, the first steps in the development of double cascade reconstruction techniques are presented.

The large-scale deep underwater Cherenkov neutrino telescopes like Baikal-GVD, ANTARES or KM3NeT, require calibration and testing methods of their optical modules.These methods usually include laser-based systems, which allow to check the telescope responses to the light and for real-time monitoring of the optical parameters of water such as absorption and scattering lengths, which show seasonal changes in natural reservoirs of water.We will present a testing method of a laser calibration system and a set of dedicated tools developed for Baikal-GVD, which includes a specially designed and built, compact, portable, and reconfigurable scanning station.This station is adapted to perform fast quality tests of the underwater laser sets just before their deployment in the telescope structure.The testing procedure includes the energy stability test of the laser device, 3D scan of the light emission from the diffuser and attenuation test of the optical elements of the laser calibration system.The test bench consists primarily of an automatic mechanical scanner with a movable Si detector, beam splitter with a reference Si detector and, optionally, Q-switched diode-pumped solid-state laser used for laboratory scans of the diffusers.The presented test bench enables a three-dimensional scan of the light emission from diffusers, which are designed to obtain the isotropic distribution of photons around the point of emission.The results of the measurement can be easily shown on a 3D plot immediately after the test and may be also implemented to a dedicated program simulating photons propagation in water, which allows to check the quality of the diffuser in the scale of the Baikal-GVD telescope geometry.

Abstract Baikal-GVD (Gigaton Volume Detector) is a neutrino telescope located in pure water of Lake Baikal. At the current stage (season 2021), detector is composed of 2304 optical modules arranged in 8 clusters. In searching for neutrino cascade events, light patterns produced via discrete stochastic energy losses along muon tracks create the most abundant background. Methods to separate cascade-like events from tracks and neutrino cascades in a single cluster have been developed and optimized. One of the method tries to find the maximum number of track hits amongst cascade hits, which are present in the muon bundle event. Other ones rely on the distributions of charges and positions of hits on optical modules associated with cascade events. All suppression methods were optimized by the Monte Carlo simulation datasets.

We describe the experimental results of a new type of electron tracker, called Hadron Blind Detector or HBD. An HBD prototype was tested with gas mixtures of CF4 with He or Ne and a parallel plate avalanche chamber having a CsI photocathode of eight pads. Beam tests confirm the large Cherenkov light bandwidth in the EUV region that can be obtained with such gas mixtures. It results in a large quality factor of about 500 cm−1 which allows HBD operation with a much shorter radiator thickness than conventional Cherenkov counters. Full electron efficiency was obtained, while pions were rejected up to momenta of 9 GeV/c. HBD is unique in measuring electron trajectories near the vertex, vetoing Dalitz pairs, and providing trigger on electrons among heavy hadron background. We discuss the use of such detectors for lepton identification and detection in high energy physics experiments and especially in heavy ion colliders.

We present searches for beyond-DGLAP resummation effects in the production of dijets with large rapidity separation in pp collisions at p s=7 TeV. Ratios of inclusive to exclusive dijet production cross sections and dijet azimuthal decorrelations are presented as a function of the rapidity separation between jets. The measurements are compared to predictions of conventional LO+PS MC generators, as well as to MC generators incorporating elements of the BFKL approach and analytic NLL BFKL calculations. Measurements of inclusive low-p T jet production in pp collisions at p s=8 TeV are also presented.

Deep underwater neutrino telescope "Dubna"the first, demonstration cluster of Baikal-GVD, has been deployed in April 2015 and was operating up to February 2016 in Lake Baikal.In 2016 this array was upgraded to baseline configuration of GVD-cluster by adding additional 96 optical modules.The next step of array extension was provided in 2017 by deployment of second GVD-cluster in Lake Baikal.We present here preliminary results of a search for cascade events using data sample recorded in 2015 by Dubna array and corresponding to 41 live days of data taking.

The Baikal-GVD is a cubic kilometer scale neutrino telescope which is deployed in Lake Baikal, that will perform neutrino astronomy studies.It consists of sub-arrays -clusters of about 300 optical modules each, that detect the Cherenkov light radiated by charged particles induced by neutrino interactions with the surrounding medium.The performance of the neutrino telescope relies on the precise timing and positioning calibration of the detector elements, continuous control and monitoring of a behavior of measuring systems, as well as environmental conditions which may affect light detection and event selection.This contribution describes the units which are used in GVD for calibration and monitoring purposes.

We study the light output, light collection efficiency and signal timing of a variety of organic scintillators that are being considered for the upgrade of the hadronic calorimeter of the CMS detector. The experimental data are collected at the H2 test-beam area at CERN, using a 150 GeV muon beam. In particular, we investigate the usage of over-doped and green-emitting plastic scintillators, two solutions that have not been extensively considered. We present a study of the energy distribution in plastic-scintillator tiles, the hit efficiency as a function of the hit position, and a study of the signal timing for blue and green scintillators.

Baikal-GVD is a kilometer-scale neutrino telescope under construction in Lake Baikal, which will be formed by multi-megaton subarrays -clusters of strings.A first demonstration cluster "Dubna" has been deployed in 2015 and comprises 192 optical modules (OMs).In 2016 this cluster was upgraded to the baseline configuration which comprises 288 OMs arranged at eight strings.The second full-scale GVD-cluster was deployed and put in operation in 2017.We review the present activity towards the GVD implementation and discuss some selected results obtained with the "Dubna" cluster.

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.

Abstract The Baikal-GVD is a neutrino telescope situated in the deepest freshwater lake in the world — Lake Baikal. The design of the Baikal-GVD trigger system allows also to study the ambient light of the lake. The analysis of the optical light activity of Baikal water, particularly, time and spatial variations of the luminescence activity for data collected in years 2018, 2019, and 2020 is presented. For the first time we observed highly luminescent layer moving upwards with maximal speed of 28 m/day in January 2021.

We present recent measurements of multijet correlations using forward and low-$p_{\mathrm{T}}$ jets performed by the CMS collaboration at the LHC collider. In pp collisions at $\sqrt{s} = 7$ TeV, azimuthal correlations in dijets separated in rapidity by up to 9.4 units were measured. The results are compared to BFKL- and DGLAP-based Monte Carlo generator and analytic predictions. In pp collisions at $\sqrt{s} = 8$ TeV, cross sections for jets with $p_{\mathrm{T}}$ > 21 GeV and |y| < 4.7, and for track-jets with $p_{\mathrm{T}}$ > 1 GeV (minijets) are presented. The minijet results are sensitive to the bound imposed by the total inelastic cross section, and are compared to various models for taming the growth of the $2 \rightarrow 2$ cross section at low $p_{\mathrm{T}}$.

We report on a measurement of the inclusive production of forward jets as well as of associated production of forward and central jets in pp collisions at √ s = 7 TeV.Forward jets are reconstructed with the anti-kT (R = 0.5) algorithm in the Hadronic Forward (HF) calorimeter at pseudorapidities 3.2 < |η| < 4.7, in the transverse momentum range p T = 35 -140 GeV/c.The single differential cross section as function of the forward and central jet transverse momentum is presented and compared to next-to-leading order perturbative QCD calculations, the PYTHIA and HERWIG parton shower event generators, as well as to the CASCADE Monte Carlo.

In this note we summarize the progress made by the calorimeter simulation task force (CALOTF) over the past year. The CALOTF was established in February 2008 in order to understand and reconcile the discrepancies observed between the CMS calorimetry simulation and test beam data recorded during 2004 and 2006. The simulation has been significantly improved by using a newer version of GEANT4 and an improved physics list for the full CMS detector simulation. Simulation times have been reduced by introducing flexible parameterizations to describe showering in the calorimeter (using a GFLASH-like approach) which have been tuned to the test beam data.

The Baikal-GVD neutrino telescope with an km3 scale detection volume is currently under construction at Lake Baikal. 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). First cluster of GVD in its baseline configuration was deployed in 2016. Spatial positions of light sensors are controlled by dedicated acoustic positioning system. The basic elements and the layout of the acoustic positioning system for the Baikal-GVD neutrino telescope are described, and selected results of system operation are presented.

Baikal-GVD is a kilometer scale neutrino telescope under construction in Lake Baikal, which will be formed by multimegaton subarrays -clusters of strings.First demonstration cluster "Dubna" has been deployed in 2015 and comprises 192 optical modules (OMs).In 2016 cluster "Dubna" was upgraded to baseline configuration which comprises 288 OMs arranged at eight strings.The second full scale GVD-cluster was deployed and put in operation in 2017 in Lake Baikal.We review a present activity towards the GVD implementation and discuss some selected results obtained with array "Dubna".

Monte Carlo event simulation with BFKL evolution is discussed. We report current status of a Monte Carlo event generator ULYSSES with BFKL evolution implemented. The ULYSSES, based on Pythia Monte Carlo generator, would help to reveal BFKL effects at LHC energies. In particular, such an observable as dijet K-factor can serve as a source of BFKL dynamics at the LHC, and it would also help to search for new physics.

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.

Cubic kilometer scale neutrino telescope Baikal-GVD is currently under construction in Lake Baikal.The detector is specially designed for search for high energies neutrinos whose sources are not yet reliably identified.Since April 2019 the telescope has been successfully operated in complex of five functionally independent clusters i.e. sub-arrays of optical modules where now are hosted 1440 OMs on 40 vertical strings.Each cluster is connected to shore by individual electro-optical cables.The effective volume of the detector for neutrino initiated cascades of relativistic particles with energy above 100 TeV has been increased up to about 0.25 km 3 .Preliminary results with data samples of 2015-2018 years are discussed.

Baikal-GVD is a cubic-kilometer scale deep-underwater neutrino detector being constructed in Lake Baikal. It is designed to detect neutrinos from $\sim$100 GeV to multi-PeV energies and beyond. Detector deployment began in Spring 2015. Since April 2020 the detector includes seven 8-string clusters carrying in total 2016 optical modules located at depths from 750 to 1275 meters. By the end of the first phase of detector construction in 2024 it is planned to deploy 15 clusters, reaching the effective volume for high-energy cascade detection of 0.75 km$^3$. The design and status of the Baikal-GVD detector and first results of data analysis are presented in this report.

Abstract The first stage of the construction of the Baikal-GVD deep underwater neutrino telescope is planned to be completed in 2024. For the second stage of the detector deployment, a data acquisition system based on fiber-optic technologies has been proposed, which will allow for increased data throughput and more flexible trigger conditions. A dedicated test facility has been built and deployed at the Baikal-GVD site to test the new technological solutions. We present the principles of operation and results of tests of the new data acquisition system.

The large-scale deep underwater Cherenkov neutrino telescopes like Baikal-GVD, ANTARES or KM3NeT, require calibration and testing methods of their optical modules. These methods usually include laser-based systems which allow to check the telescope responses to the light and for real-time monitoring of the optical parameters of water such as absorption and scattering lengths, which show seasonal changes in natural reservoirs of water. We will present a testing method of a laser calibration system and a set of dedicated tools developed for Baikal- GVD, which includes a specially designed and built, compact, portable, and reconfigurable scanning station. This station is adapted to perform fast quality tests of the underwater laser sets just before their deployment in the telescope structure, even on ice, without darkroom. The testing procedure includes the energy stability test of the laser device, 3D scan of the light emission from the diffuser and attenuation test of the optical elements of the laser calibration system. The test bench consists primarily of an automatic mechanical scanner with a movable Si detector, beam splitter with a reference Si detector and, optionally, Q-switched diode-pumped solid-state laser used for laboratory scans of the diffusers. The presented test bench enables a three-dimensional scan of the light emission from diffusers, which are designed to obtain the isotropic distribution of photons around the point of emission. The results of the measurement can be easily shown on a 3D plot immediately after the test and may be also implemented to a dedicated program simulating photons propagation in water, which allows to check the quality of the diffuser in the scale of the Baikal-GVD telescope geometry.

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.

Abstract We describe the experimental results of a new type of electron tracker, called Hadron Blind Detector or HBD. An HBD prototype was tested with gas mixtures of CF4 with He or Ne and a parallel plate avalanche chamber having a CsI photocathode of eight pads. Beam tests confirm the large Cherenkov light bandwidth in the EUV region that can be obtained with such gas mixtures. It results in a large quality factor of about 500 cm−1 which allows HBD operation with a much shorter radiator thickness than conventional Cherenkov counters. Full electron efficiency was obtained, while pions were rejected up to momenta of 9 GeV/c. HBD is unique in measuring electron trajectories near the vertex, vetoing Dalitz pairs, and providing trigger on electrons among heavy hadron background. We discuss the use of such detectors for lepton identification and detection in high energy physics experiments and especially in heavy ion colliders.