The Scattering and Neutrino Detector at the LHC (SND@LHC) started taking data at the beginning of Run 3 of the LHC. The experiment is designed to perform measurements with neutrinos produced in proton-proton collisions at the LHC in an energy range between 100 GeV and 1 TeV. It covers a previously unexplored pseudo-rapidity range of $$7.2<\eta <8.4$$7.2 < η < 8.4 . The detector is located 480 m downstream of the ATLAS interaction point in the TI18 tunnel. It comprises a veto system, a target consisting of tungsten plates interleaved with nuclear emulsion and scintillating fiber (SciFi) trackers, followed by a muon detector (UpStream, US and DownStream, DS). In this article we report the measurement of the muon flux in three subdetectors: the emulsion, the SciFi trackers and the DownStream Muon detector. The muon flux per integrated luminosity through an 18 $$\times $$× 18 cm $$^{2}$$2 area in the emulsion is: $$\begin{aligned} 1.5 \pm 0.1(\text {stat}) \times 10^4\,\text {fb/cm}^{2}. \end{aligned}$$1.5 ± 0.1 ( stat ) × 10 4 fb/cm 2 . The muon flux per integrated luminosity through a 31 $$\times $$× 31 cm $$^{2}$$2 area in the centre of the SciFi is: $$\begin{aligned} 2.06\pm 0.01(\text {stat})\pm 0.12(\text {sys}) \times 10^{4} \text {fb/cm}^{2} \end{aligned}$$2.06 ± 0.01 ( stat ) ± 0.12 ( sys ) × 10 4 fb/cm 2 The muon flux per integrated luminosity through a 52 $$\times $$× 52 cm $$^{2}$$2 area in the centre of the downstream muon system is: $$\begin{aligned} 2.35\pm 0.01(\text {stat})\pm 0.10(\text {sys}) \times 10^{4}\,\text {fb/cm}^{2} \end{aligned}$$2.35 ± 0.01 ( stat ) ± 0.10 ( sys ) × 10 4 fb/cm 2 The total relative uncertainty of the measurements by the electronic detectors is 6 $$\%$$% for the SciFi and 4 $$\%$$% for the DS measurement. The Monte Carlo simulation prediction of these fluxes is 20–25 $$\%$$% lower than the measured values.

Phenomena have been observed in mountain high-energy cosmic-ray experiments, namely, a delayed absorption of high-energy cascades initiated by cosmic-ray hadrons in a lead absorber at $E_0\gtrsim {10}^{14} \mathrm{e}\mathrm{V}$ (so-called long-flying component), a coplanarity of most energetic particles in the central region of γ-ray−hadron superfamilies, and the so-called Tien Shan effect in EAS cores at $E_0\gtrsim {10}^{16} \mathrm{e}\mathrm{V} \left(\sqrt{s}>5 \mathrm{T}\mathrm{e}\mathrm{V}\right)$. These effects are not described by theoretical models. The coplanarity is explained by the process of coplanar generation of most energetic secondary particles in interactions of superhigh-energy hadrons with the nuclei of air atoms. The other two phenomena are possibly explained with a high cross section for fragmentation-region charmed-hadron generation. To investigate these phenomena, a cosmic-ray detector array, including a very thick ionization calorimeter, is being upgraded to study EAS cores.

During 2022/2023 the optimal inefficiency of the Veto system of the SND@LHC detector was measured to be (7.8 ± 2.8) × 10^-8. To reduce this inefficiency, a third Veto plane was installed during the 2023-2024 Year End Technical Stop. In addition, the Veto system was lowered to cover the target fully, thereby increasing acceptance. This paper describes how the inefficiency of the Veto system was reduced from (7.8 ± 2.8) × 10^-8 with an acceptance of about 64% of the target area in 2022-2023 to (4.9 ± 1.9) × 10^-9 on the full area in 2024.

After rapid approval and installation, the SND@LHC Collaboration was able to gather data successfully in 2022 and 2023. Neutrino interactions from ν_μs originating at the LHC IP1 were observed. Since muons constitute the major background for neutrino interactions, the muon flux entering the acceptance was also measured. To improve the rejection power of the detector and to increase the fiducial volume, a third Veto plane was recently installed. The energy resolution of the calorimeter system was measured in a test beam. This will help with the identification of ν_e interactions that can be used to probe charm production in the pseudo-rapidity range of SND@LHC (7.2 < η < 8.4). Events with three outgoing muons have been observed and are being studied. With no vertex in the target, these events are very likely from muon trident production in the rock before the detector. Events with a vertex in the detector could be from trident production, photon conversion, or positron annihilation. To enhance SND@LHC’s physics case, an upgrade is planned for HL-LHC that will increase the statistics and reduce the systematics. The installation of a magnet will allow the separation of ν_μ from ${\overline{\nu }}_{\mu }$

The problem of the boundaries of the Mendeleev table of chemical elements is closely related to the understanding of the properties of nuclear matter. In this regard, the synthesis of superheavy nuclei on accelerators and the registration of their decay products are of fundamental scientific interest. The Joint Institute of Nuclear Research in Dubna (JINR) conducts research on the synthesis of superheavy nuclei on the new DC-280 cyclotron (the Factory of Superheavy Elements). As part of the development of this experiment, the possibility of using phosphate glass as a material for detectors of heavy and superheavy nuclei is being considered. This issue requires test experiments to study the recording properties of the glass at different irradiation and treatment conditions. The article presents a method for identifying heavy ions in phosphate glass detectors under various conditions by the geometric characteristics of ion tracks. The results obtained indicate the possibility of using the KNFS-3 phosphate glass detectors for registration and identification of accelerated superheavy nuclei.

In high-altitude experiments to study the central cores of EAS at E₀ ≳ 10¹⁶ eV (√s ≳ 5 TeV) using X-ray emulsion chambers and ionization calorimeters, phenomena such as the coplanarity of the arrival of the most energetic particles in super families of γ-rays and hadrons and a so-called Tien Shan effect (too slow absorption of cascades initiated by high-energy hadrons in the calorimeter) were observed. These effects could not be reproduced within the framework of theoretical models of the 80s and 90s. The coplanarity is explained via a process of coplanar generation of the most energetic secondary particles in interactions of super high-energy hadrons with nuclei of air atoms. Perhaps the Tien Shan effect could be explained using a high cross section for the generation of fragmentation-region charmed hadrons. To study these phenomena, a new set of detectors has been developed, including the world’s highest high-mountain ionization calorimeter, “Hadron-55”. This paper presents the initial experimental results.