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 Depero, E.; Andreev, Yu. M.; Banerjee, D. ...
The European physical journal. C, Particles and fields,
12/2020, Letnik:
80, Številka:
12
Journal Article
Recenzirano
Odprti dostop
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.
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.
An integrated approach is applied to reveal fine changes in the surface-normal structure of 1,2-dimyristoyl-sn-glycero-3-phospho-l-serine (DMPS) monolayers at the air–lipid–water interface occurring ...in a liquid expanded (LE)–liquid condensed (LC) transition. The combination of the Langmuir monolayer technique, X-ray reflectometry, and molecular dynamics (MD) modeling provides new insight into the molecular nature of electrostatic phenomena in different stages of lipid compression. A homemade setup with a laboratory X-ray source (λ = 1.54 Å) offers a nondestructive way to reveal the structural difference between the LE and LC phases of the lipid. The electron density profile in the direction normal to the interface is recovered from the X-ray reflectivity data with the use of both model-independent and model-based approaches. MD simulations of the DMPS monolayer are performed for several areas per lipid using the all-atom force field. Using the conventional theory of capillary waves, a comparison is made between the electron density profiles reconstructed from the X-ray data and those calculated directly from MD modeling, which demonstrates remarkable agreement between the experiment and simulations for all selected lipid densities. This confirms the validity of the simulations and allows an analysis of the contributions of the hydrophobic tails and hydrated polar groups to the electron density profile and to the dipole component of the electric field at the interface. According to the MD data, the dependence of the Volta potential on the area per lipid in the monolayer has a different molecular nature below and above the phase transition. In the LE state of the monolayer, the potential is determined mostly by the oriented water molecules in the polar region of the lipid. In the LE–LC transition, these molecules are displaced to the bulk, and their effect on the Volta potential becomes insignificant compared with the contribution of the hydrophobic tails. The hydrophobic tails are highly ordered in the state of the liquid crystal so that their dipole moments entirely determine the growth of the potential upon compression up to the monolayer collapse.
The study was dedicated to investigation of some hemostasis and endothelial dysfunction factors association with probability of presence of vulnerable atherosclerotic plaques in coronary arteries in ...men with atherosclerosis.
The blood levels of factor VII, factor XII and MCP-1 were higher, and concentration of sVCAM-1 lower in men with vulnerable atherosclerotic plaques in the coronary arteries, compared to men who had stable plaques. Have been revealed correlation links between the blood levels of factor II, factor XII, MCP-1 and the presence of vulnerable atherosclerotic plaques in the coronary arteries. Results of logistic regression analysis showed that the relative risk of present of vulnerable atherosclerotic plaques in the coronary arteries is associated with an elevated blood level of factor XII and MCP-1.
A technology for producing a nanocomposite based on the borsiloxane polymer and aluminum oxide nanoparticles (Al2O3 NPs) has been developed. Nanocomposites containing 0.001, 0.01, and 0.1 wt% Al2O3 ...NPs have been created. It has been shown that the nanocomposite with any content of Al2O3 NPs did not lose the main rheological properties of borsiloxane. The resulting nanomaterial is capable of generating reactive oxygen species (ROS) such as hydrogen peroxide and hydroxyl radicals. The rate of ROS generation increases up to 3 times with an increase in the concentration of Al2O3 NPs. It has been shown that the nanocomposite leads to the formation of long-lived reactive protein species, and is also the reason for the appearance of such a key biomarker of oxidative stress as 8-oxoguanine in DNA. The intensity of the process increases with an increase in the concentration of Al2O3 NPs. Moreover, it was found that bacterial cells adhere to the surfaces of the nanocomposite (reduces the number of bacteria on the substrate by 39 times), and the nanocomposite can detach bacterial cells not only from the surfaces, but also from wetted substrates. The ability to capture bacterial cells is primarily associated with the properties of the polymer; they are weakly affected Al2O3 NPs. The nanocomposite is non-toxic to eukaryotic cells, the surface of the nanocomposite is suitable for eukaryotic cells for colonization. Due to unique physical properties, low cytotoxicity and antimicrobial action, this nanocomposite can be used in medicine and prosthetics.
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•A new composite based on borsilaxane and aluminum oxide NP has been obtained.•The mechanical and physicochemical properties of the composite have been studied.•Composite inhibits bacteria growth and does not affect growth of animal cells.•The antibacterial effect is probably based on the ability to damage biopolymers.•The composite can be used in the food or textile industry.
The aggregation phenomena in aqueous solutions of hydrophobically modified (HM) chitosan, containing 4 mol % of n-dodecyl side chains, were studied by viscometry and fluorescence spectroscopy with ...pyrene as a probe. The results are compared with those for unmodified chitosan. Surprisingly, fluorescence data reveal the appearance of intermolecular hydrophobic aggregates both in chitosan and in HM chitosan. Nevertheless, these polymers exhibit quite different rheological properties: upon the formation of aggregates the viscosity of HM chitosan sharply increases, while that of unmodified chitosan raises only slightly. The aggregation models for both chitosan and its hydrophobic derivative were proposed. It was shown that in solutions of HM chitosan two types of hydrophobic domains exist: hydrophobic domains typical for different associating polymers with hydrophobic side chains and hydrophobic domains inherent to chitosan itself.
The review analyzes research over the past 20−25 years in the field of physical chemistry of complexation of humic acids with cations, including radionuclides, in aqueous solutions. Problems have ...been identified in describing the reactivity of humate complexes with consideration for the objective complexity of the chemical nature of humic acids as one of the main classes of natural organic matter. The main methods of modeling complexation with humic acids, experimental methods for separating humate complexes and unbound cations (ultrafiltration, dialysis, etc.), and direct instrumental (electrochemical and spectroscopic) methods for detecting complexes were considered. Attention was also paid to the practical aspect of using humic acids for the treatment of natural water and wastewater to remove pollutants—heavy metals and radionuclides. Published data on the sorption capacity of humic acids of various origins in relation to heavy metal cations and quantitative data characterizing the stability of humate complexes were analyzed.
DNA sequencing is an essential task of modern molecular genetic research. Its fundamental parameter is the accuracy of decoding. In this work, we determined the maximum lengths of DNA fragments, ...obtained by the Sanger method and sequenced with an accuracy of 99%, in a polymer based on linear poly(
N
,
N
-dimethylacrylamide) PDMA-6 for capillaries 50 cm long to the optical window of the detector of a Nanophore 05 domestic genetic analyzer and an imported GA 3500xL genetic analyzer. The results of DNA sequencing obtained by various analysis algorithms were compared. The parameters of the analysis algorithms were selected, ensuring best results of DNA sequencing in using the PDMA-6 polymer.
We compare transverse structure evolution and energy deposition into the medium within focused multifilament arrays created using two different types of diffraction optical elements (DOEs): TEM 11 ...phase plate and a Dammann grating. We show that the employment of the Dammann grating provides a robust way to create regular multifilament arrays, which is far less dependent on laser beam quality than one using the phase plate.