First Results in the Search for Dark Sectors at NA64 with the CERN SPS High Energy Muon Beam.

We report the first search for dark sectors performed at the NA64 experiment employing a high energy muon beam and a missing energy-momentum technique. Muons from the M2 beamline at the CERN Super Proton Synchrotron with a momentum of 160 GeV/c are directed to an active target. The signal signature consists of a single scattered muon with momentum <80 GeV/c in the final state, accompanied by missing energy, i.e., no detectable activity in the downstream calorimeters. For a total dataset of (1.98±0.02)×10^{10} muons on target, no event is observed in the expected signal region. This allows us to set new limits on the remaining (m_{Z^{'}},g_{Z^{'}}) parameter space of a new Z^{'} (L_{µ}-L_{τ}) vector boson which could explain the muon (g-2)_{µ} anomaly. Additionally, our study excludes part of the parameter space suggested by the thermal dark matter relic abundance. Our results pave the way to explore dark sectors and light dark matter with muon beams in a unique and complementary way to other experiments.

Search for Light Dark Matter with NA64 at CERN.

Thermal dark matter models with particle χ masses below the electroweak scale can provide an explanation for the observed relic dark matter density. This would imply the existence of a new feeble interaction between the dark and ordinary matter. We report on a new search for the sub-GeV χ production through the interaction mediated by a new vector boson, called the dark photon A^{'}, in collisions of 100 GeV electrons with the active target of the NA64 experiment at the CERN SPS. With 9.37×10^{11} electrons on target collected during 2016-2022 runs NA64 probes for the first time the well-motivated region of parameter space of benchmark thermal scalar and fermionic dark matter models. No evidence for dark matter production has been found. This allows us to set the most sensitive limits on the A^{'} couplings to photons for masses m_{A^{'}}≲0.35 GeV, and to exclude scalar and Majorana dark matter with the χ-A^{'} coupling α_{D}≤0.1 for masses 0.001≲m_{χ}≲0.1 GeV and 3m_{χ}≤m_{A^{'}}.

Results from the Baksan Experiment on Sterile Transitions (BEST).

The Baksan Experiment on Sterile Transitions (BEST) was designed to investigate the deficit of electron neutrinos ν_{e} observed in previous gallium-based radiochemical measurements with high-intensity neutrino sources, commonly referred to as the "gallium anomaly," which could be interpreted as evidence for oscillations between ν_{e} and sterile neutrino (ν_{s}) states. A 3.414-MCi ^{51}Cr ν_{e} source was placed at the center of two nested Ga volumes and measurements were made of the production of ^{71}Ge through the charged current reaction, ^{71}Ga(ν_{e},e^{-})^{71}Ge, at two average distances. The measured production rates for the inner and the outer targets, respectively, are [54.9_{-2.4}^{+2.5}(stat)±1.4(syst)] and [55.6_{-2.6}^{+2.7}(stat)±1.4(syst)] atoms of ^{71}Ge/d. The ratio (R) of the measured rate of ^{71}Ge production at each distance to the expected rate from the known cross section and experimental efficiencies are R_{in}=0.79±0.05 and R_{out}=0.77±0.05. The ratio of the outer to the inner result is 0.97±0.07, which is consistent with unity within uncertainty. The rates at each distance were found to be similar, but 20%-24% lower than expected, thus reaffirming the anomaly. These results are consistent with ν_{e}→ν_{s} oscillations with a relatively large Δm^{2} (>0.5 eV^{2}) and mixing sin^{2}2θ (≈0.4).

Search for a New B-L Z

A search for a new Z^{'} gauge boson associated with (un)broken B-L symmetry in the keV-GeV mass range is carried out for the first time using the missing-energy technique in the NA64 experiment at the CERN SPS. From the analysis of the data with 3.22×10^{11} electrons on target collected during 2016-2021 runs, no signal events were found. This allows us to derive new constraints on the Z^{'}-e coupling strength, which, for the mass range 0.3≲m_{Z^{'}}≲100 MeV, are more stringent compared to those obtained from the neutrino-electron scattering data.

Constraints on New Physics in Electron g-2 from a Search for Invisible Decays of a Scalar, Pseudoscalar, Vector, and Axial Vector.

We performed a search for a new generic X boson, which could be a scalar (S), pseudoscalar (P), vector (V), or an axial vector (A) particle produced in the 100 GeV electron scattering off nuclei, e^{-}Z→e^{-}ZX, followed by its invisible decay in the NA64 experiment at CERN. No evidence for such a process was found in the full NA64 dataset of 2.84×10^{11} electrons on target. We place new bounds on the S, P, V, A coupling strengths to electrons, and set constraints on their contributions to the electron anomalous magnetic moment a_{e}, |Δa_{X}|≲10^{-15}-10^{-13} for the X mass region 1 MeV≲m_{X}≲1 GeV. These results are an order of magnitude more sensitive compared to the current accuracy on a_{e} from the electron g-2 experiments and recent high-precision determination of the fine structure constant.

Search for Axionlike and Scalar Particles with the NA64 Experiment.

We carried out a model-independent search for light scalar (s) and pseudoscalar axionlike (a) particles that couple to two photons by using the high-energy CERN SPS H4 electron beam. The new particles, if they exist, could be produced through the Primakoff effect in interactions of hard bremsstrahlung photons generated by 100 GeV electrons in the NA64 active dump with virtual photons provided by the nuclei of the dump. The a(s) would penetrate the downstream HCAL module, serving as a shield, and would be observed either through their a(s)→γγ decay in the rest of the HCAL detector, or as events with a large missing energy if the a(s) decays downstream of the HCAL. This method allows for the probing of the a(s) parameter space, including those from generic axion models, inaccessible to previous experiments. No evidence of such processes has been found from the analysis of the data corresponding to 2.84×10^{11} electrons on target, allowing us to set new limits on the a(s)γγ-coupling strength for a(s) masses below 55 MeV.

Dark Matter Search in Missing Energy Events with NA64.

A search for sub-GeV dark matter production mediated by a new vector boson A^{'}, called a dark photon, is performed by the NA64 experiment in missing energy events from 100 GeV electron interactions in an active beam dump at the CERN SPS. From the analysis of the data collected in the years 2016, 2017, and 2018 with 2.84×10^{11} electrons on target no evidence of such a process has been found. The most stringent constraints on the A^{'} mixing strength with photons and the parameter space for the scalar and fermionic dark matter in the mass range ≲0.2 GeV are derived, thus demonstrating the power of the active beam dump approach for the dark matter search.

Search for a Hypothetical 16.7 MeV Gauge Boson and Dark Photons in the NA64 Experiment at CERN.

We report the first results on a direct search for a new 16.7 MeV boson (X) which could explain the anomalous excess of e^{+}e^{-} pairs observed in the excited ^{8}Be^{*} nucleus decays. Because of its coupling to electrons, the X could be produced in the bremsstrahlung reaction e^{-}Z→e^{-}ZX by a 100 GeV e^{-} beam incident on an active target in the NA64 experiment at the CERN Super Proton Synchrotron and observed through the subsequent decay into a e^{+}e^{-} pair. With 5.4×10^{10} electrons on target, no evidence for such decays was found, allowing us to set first limits on the X-e^{-} coupling in the range 1.3×10^{-4}≲ε_{e}≲4.2×10^{-4} excluding part of the allowed parameter space. We also set new bounds on the mixing strength of photons with dark photons (A^{'}) from nonobservation of the decay A^{'}→e^{+}e^{-} of the bremsstrahlung A^{'} with a mass ≲23 MeV.

Search for Invisible Decays of Sub-GeV Dark Photons in Missing-Energy Events at the CERN SPS.

We report on a direct search for sub-GeV dark photons (A^{'}), which might be produced in the reaction e^{-}Z→e^{-}ZA^{'} via kinetic mixing with photons by 100 GeV electrons incident on an active target in the NA64 experiment at the CERN SPS. The dark photons would decay invisibly into dark matter particles resulting in events with large missing energy. No evidence for such decays was found with 2.75×10^{9} electrons on target. We set new limits on the γ-A^{'} mixing strength and exclude the invisible A^{'} with a mass ≲100 MeV as an explanation of the muon g_{µ}-2 anomaly.

Probing the explanation of the muon (g-2) anomaly and thermal light dark matter with the semi-visible dark photon channel.

We report the results of a search for a new vector boson ( A ' ) decaying into two dark matter particles χ 1 χ 2 of different mass. The heavier χ 2 particle subsequently decays to χ 1 and an off-shell Dark Photon A ' ∗ → e + e - . For a sufficiently large mass splitting, this model can explain in terms of new physics the recently confirmed discrepancy observed in the muon anomalous magnetic moment at Fermilab. Remarkably, it also predicts the observed yield of thermal dark matter relic abundance. A detailed Monte-Carlo simulation was used to determine the signal yield and detection efficiency for this channel in the NA64 setup. The results were obtained re-analyzing the previous NA64 searches for an invisible decay A ' → χ χ ¯ and axion-like or pseudo-scalar particles a → γ γ . With this method, we exclude a significant portion of the parameter space justifying the muon g-2 anomaly and being compatible with the observed dark matter relic density for A ' masses from 2 m e up to 390 MeV and mixing parameter ε between 3 × 10 - 5 and 2 × 10 - 2 .

Hunting down the X17 boson at the CERN SPS.

Recently, the ATOMKI experiment has reported new evidence for the excess of e + e - events with a mass ∼ 17 MeV in the nuclear transitions of 4 He, that they previously observed in measurements with 8 Be. These observations could be explained by the existence of a new vector X 17 boson. So far, the search for the decay X 17 → e + e - with the NA64 experiment at the CERN SPS gave negative results. Here, we present a new technique that could be implemented in NA64 aiming to improve the sensitivity and to cover the remaining X 17 parameter space. If a signal-like event is detected, an unambiguous observation is achieved by reconstructing the invariant mass of the X 17 decay with the proposed method. To reach this goal an optimization of the X 17 production target, as well as an efficient and accurate reconstruction of two close decay tracks, is required. A dedicated analysis of the available experimental data making use of the trackers information is presented. This method provides independent confirmation of the NA64 published results [1], validating the tracking procedure. The detailed Monte Carlo study of the proposed setup and the background estimate show that the goal of the proposed search is feasible.

Analysis of chaotic and noise processes in a fluctuating blood flow using the Allan variance technique.

OBJECTIVE: The aim of this work was to develop a novel technique for digital processing of Doppler ultrasound blood flow sensor data from noisy blood flow velocity waveforms. METHODS: To evaluate the fluctuating blood flow parameters, various nonlinear dynamics methods and algorithms are often being used. Here, for identification of chaotic and noise components in a fluctuating coronary blood flow, for the first time the Allan variance technique was used. Analysis of different types of noises (White, Brownian, Flicker) was carried out and their strong correlation with fractality of time series (the Hurst exponent) was revealed. RESULTS: Based on a specialized software realizing the developed technique, numerical experiments with real clinical data were carried out. Recommendations for identification of noisy patterns of coronary blood flow in normal and pathological states were developed. CONCLUSION: The methodology gives us the possibility for the more detailed quantitative and qualitative analysis of a noisy fluctuating blood flow data.

Tick-borne encephalitis virus strains of Western Siberia.

Tick-borne encephalitis virus (TBEV) strains were isolated from ticks in Western Siberia for 12 years. Molecular hybridization of the 46 viral RNA with the TBEV cDNA and oligonucleotide probes revealed differences between the Siberian and Far Eastern strains. A comparison of the viral E gene fragment nucleotide sequence showed 89-98% homology between Siberian TBEV strains, whereas their similarity with strains from other populations was less than 83%. However, the viral E and NS1 glycoprotein antigenic structures appeared to be conservative because of the degenerate genetic code. This was shown by enzyme-linked immunosorbent assay with the corresponding monoclonal antibodies (MAb). The single exception was the MAb 17C3 against nonstructural glycoprotein NS1, which could distinguish Siberian from Far Eastern strains. Moreover, the neurovirulence differed between strains from the two natural populations. Lower neuroinvasiveness of the Siberian strains in comparison with Far Eastern Sofyin strain might be caused by both E and NS1 glycoprotein mutations.

[Using inter-SINE-PCR to study mammalian phylogeny]. / Opyt ispol'zovaniia inter-SINE-PTsR v izuchenii filogeneza mlekopitaiushchikh.

Results of the use of the fingerprinting method related to short interspersed elements (SINEs), inter-SINE-PCR, in the study of phylogenetic and taxonomic relationship in mammals from orders Chiroptera (family Vespertilionidae) and Lipotyphla (family Erinaceidae) are reported. The inter-SINE-PCR method is based on the amplification of fragments situated between copies of SINEs, which are short retroposons spaced 100 to 1000 bp apart. Specifically selected primers were used, which are complementary to consensus sequences of two short retroposons: the mammalian interspersed repeat (MIR), which is typical of all mammals and some other vertebrates, was used in the cases of bats and Erinaceidae, and the ERI-1 element recently isolated from the genome of the Daurian hedgehog was used in the case of Erinaceidae. The results support the current view on phylogenetic relationship between hedgehogs belonging to genera Erinaceus, Hemiechinus, and Paraechinus (but not the genus Atelerix). In bats, the phylogenetic reconstruction revealed a statistically valid topology only at lower taxonomic levels, whereas the topology for the genus and supragenus ranks was unresolved and fan-shaped. The benefits and limitations of the inter-SINE-PCR method are discussed.

[Lymphocyte blast transformation to HBsAg and HBcAg in patients with various clinical forms of hepatitis B]. / Blasttransformatsiia limfotsitov na HBsAg i HBcAg u bol'nykh s razlichnymi klinicheskimi formami gepatita B.

Sensitization of the peripheral blood lymphocytes to HBsAg and HBcAg in 51 patients with acute hepatitis B (HB) in the time course of infection, in 13 with chronic active hepatitis B (CAH) and 8 HBsAg carriers was studied by lymphocyte blastogenesis assay. In patients with mild or moderately severe forms of acute HB at the peak of the disease lymphocyte blastogenic response to HBcAg was observed; sensitization to HBsAg was lacking and could be detected only in the stage of convalescence when the specific response to HBcAg was already undetectable in most patients. No lymphocyte sensitization to HBsAg either at the peak of the disease or in convalescence was observed in patients with a lingering form of acute HB as well as in those with CAH and HBsAg carriers. At the peak of severe HB blastogenic response was demonstrated to both antigens under study but was more marked to HBcAg. Most patients with CAH showed lymphocyte blastogenic response to HBcAg. It is concluded that specific lymphocyte response to HBV antigens varies in relation to the severity and course of the infection.

[The pharmacokinetics of recombinant alpha 2-interferon (reaferon)]. / Farmakokinetika rekombinantnogo al'fa 2-interferona (reaferona).

The use of electrochemical iodination under potentiostatic conditions resulted in generating 131I-labeled alpha 2-interferon (IF) the antiviral activity of which differed statistically insignificantly from that of the intact preparation. The resulting radioactive analogue of alpha 2-IF was successfully used for the study of pharmacokinetics of reaferon (RFN) in experimental animals which determined the parameters of the processes of its elimination from the blood stream, accumulation and release from the liver, the organ in which the highest accumulation of alpha 2-IF is observed. It is concluded from the foregoing that it would be expedient to use RFN for treatment of viral disease of the liver and the lungs.

[Polyethylene oxide-based artificial antigens. An experimental study of the kinetics of the distribution of polyethylene oxide derivatives]. / Iskusstvennye antigeny na osnove polietilenoksida. Eksperimental'noe izuchenie kinetiki raspredeleniia proizvodnykh polietilenoksida.

125I-labeled derivatives of iodaryl-polyethylene oxide with mol. wt. equal to 3 X 10(3), containing and not containing dinitrophenyl (DNP) residues (haptens), were obtained. The capacity for anti-DNP response was shown to be unaffected by the presence of the iodaryl group. The pharmacokinetics of both derivatives of polyethylene oxide were studied in experiments on noninbred white rats receiving these derivatives intravenously in doses of 0.53-0.80 mg/kg. These experiments revealed the following differences in the pharmacokinetics of the derivatives under study: the presence of the DNP group led to an increase in the level of polymer fixation in the body of the animals, particularly in their blood, liver and spleen. Differences in the content of radioactive substances in other organs were not statistically significant.

[An epidemiological study of herpetic viral infections in the Republic of Byelarus]. / Izuchenie épidemiologii gerpeticheskikh virusnykh infektsii v Respublike Belarus'.

Studies on the epidemiology of infections caused by Herpes simplex virus, cytomegalovirus and Epstein-Barr virus in different age groups of the population of the Republic of Belarus, carried out over the period of many years, are summarized. The frequency of clinical manifestations of different forms of herpetic viral pathology in newborns, children and adults in different regions of the republic was studied. More frequent cases of the most severe clinical forms of herpetic viral infections (encephalitides, generalized infection) were noted in persons having immunodeficient states of different etiology, as well as among the population residing on the territory with unfavorable radiation conditions as a consequence of the catastrophe in the Chernobyl nuclear electric power station. For further study of the specific features of the epidemiology of herpetic obligatory registration of all cases of herpetic viral infections, starting from January 1, 1996, was introduced.

[The outcome of viral hepatitis B and cellular immunity function]. / Iskhody virusnogo gepatita B i sostoianie kletochnogo immuniteta.

Immunological examination of 158 patients with viral type B hepatitis (VH) was performed over time. Patients with HBsAg elimination for 60 days from the onset of jaundice and a favorable outcome of hepatitis at the height of the process demonstrated a decrease in the relative number of theophylline resistant lymphocytes (T-helpers), a decrease in theophylline sensitive lymphocytes (T-suppressors), an increase in the helper/suppressor (H/S) ratio up to 13.1/1 (the normal ratio being 3.9/1), a certain increase in the number of B-lymphocytes, activation of rosette-forming function of neutrophils, and a tendency to an increase in the activity of natural killer cells (NK). Patients with HBs-antigenemia over 60 days with subsequent convalescence also demonstrated similar changes of immunoregulating T-lymphocyte subpopulations but they developed later in relation to the onset of viral hepatitis. In the formation of chronic persistent hepatitis (CPH) there was no decrease in the absolute and relative number of T-suppressors from the onset of disease, the level of T-helpers and the H/S ratio were moderately lowered. Unlike CPH the suppression of the effector link of the immune system (phagocytosis and NK) and a decrease in the level of T-suppressors were noted in the development of chronic active hepatitis in all the periods of the process. The application of the above regularities to prognosis of VH outcomes, the choice and assessment of efficacy of immunocorrective therapy was discussed.

A moiré deflectometer for antimatter.

The precise measurement of forces is one way to obtain deep insight into the fundamental interactions present in nature. In the context of neutral antimatter, the gravitational interaction is of high interest, potentially revealing new forces that violate the weak equivalence principle. Here we report on a successful extension of a tool from atom optics--the moiré deflectometer--for a measurement of the acceleration of slow antiprotons. The setup consists of two identical transmission gratings and a spatially resolving emulsion detector for antiproton annihilations. Absolute referencing of the observed antimatter pattern with a photon pattern experiencing no deflection allows the direct inference of forces present. The concept is also straightforwardly applicable to antihydrogen measurements as pursued by the AEgIS collaboration. The combination of these very different techniques from high energy and atomic physics opens a very promising route to the direct detection of the gravitational acceleration of neutral antimatter.