The exact tree-level calculation of the dark photon production in high-energy electron scattering at the CERN SPS

Dark photon ($A'$) that couples to the standard model fermions via the kinetic mixing with photons and serves as a mediator of dark matter production could be observed in the high-energy electron scattering $e^- + Z ~\rightarrow e^- + Z + A'$ off nuclei followed by the $A' \to invisible$ decay. We have performed the exact, tree-level calculations of the $A'$ production cross sections and implemented them in the program for the full simulation of such events in the experiment NA64 at the CERN SPS. Using simulations results, we study the missing energy signature for the bremsstrahlung $A' \rightarrow$ invisible decay that permits the determination of the $\gamma-A'$ mixing strength in a wide, from sub-MeV to sub-GeV, $A'$ mass range. We refine and expand our earlier studies of this signature for discovering $A'$ by including corrections to the previously used calculations based on the improved Weizsaker-Williams approximation, which turn out to be significant. We compare our cross sections values with the results from other calculations and find a good agreement between them. The possibility of future measurements with high-energy electron beams and the sensitivity to $A'$ are briefly discussed.Comment: 11 pages, 6 figures, revised version, improved cross-section integrator is used, comparison with bremsstrahlung spectrum is added, final conclusions remain unchange

Missing energy signature from invisible decays of dark photons at the CERN SPS

The dark photon ($A'$) production through the mixing with the bremsstrahlung photon from the electron scattering off nuclei can be accompanied by the dominant invisible $A'$ decay into dark-sector particles. In this work we discuss the missing energy signature of this process in the experiment NA64 aiming at the search for $A'\to invisible$ decays with a high-energy electron beam at the CERN SPS. We show the distinctive distributions of variables that can be used to distinguish the $A'\to invisible$ signal from background. The results of the detailed simulation of the detector response for the events with and without $A'$ emission are presented. The efficiency of the signal event selection is estimated. It is used to evaluate the sensitivity of the experiment and show that it allows to probe the still unexplored area of the mixing strength $10^{-6}\lesssim \epsilon \lesssim 10^{-2}$ and masses up to $M_{A'} \lesssim 1$ GeV. The results obtained are compared with the results from other calculations. In the case of the signal observation, a possibility of extraction of the parameters $M_{A'}$ and $\epsilon$ by using the missing energy spectrum shape is discussed. We consider as an example the $A'$ with the mass 16.7 MeV and mixing $\epsilon \lesssim 10^{-3}$, which can explain an excess of events recently observed in nuclear transitions of an excited state of $^8$Be. We show that if such $A'$ exists its invisible decay can be observed in NA64 within a month of running, while data accumulated during a few months would allow also to determine the $\epsilon$ and $M_{A'}$ parameters.Comment: 12 pages, 15 figures. Revised versio

Applicability of QKD: TerraQuantum view on the NSA's scepticism

Quantum communication offers unique features that have no classical analog, in particular, it enables provably secure quantum key distribution (QKD). Despite the benefits of quantum communication are well understood within the scientific community, the practical implementations sometimes meet with scepticism or even resistance. In a recent publication [1], NSA claims that QKD is inferior to "quantum-resistant" cryptography and does not recommend it for use. Here we show that such a sceptical approach to evaluation of quantum security is not well justified. We hope that our arguments will be helpful to clarify the issue

Heat switch and thermoelectric effects based on Cooper-pair splitting and elastic cotunneling

In this paper, we demonstrate that the hybrid normal-superconducting-normal (NSN) structure has potential for a multifunctional thermal device which could serve for heat flux control and cooling of microstructures. By adopting the scattering matrix approach, we theoretically investigate thermal and electrical effects emerging in such structures due to the Cooper pair splitting (CPS) and elastic cotunneling phenomena. We show that a finite superconductor can, in principle, mediate heat flow between normal leads, and we further clarify special cases when this seems contradictory to the second law of thermodynamics. Among other things, we demonstrate that the CPS phenomenon can appear even in the simple case of a ballistic NSN structure.Comment: 10 pages, 5 figure

Investigation of the interaction of ion beams and X-ray quanta with deuterated crystal structures at the HELIS facility

The results of studies of the interaction of ion beams and X-ray quanta with deuterated crystal structures at the HELIS facility (LPI) are presente

Real-Time Water Quality Monitoring with Chemical Sensors

Water quality is one of the most critical indicators of environmental pollution and it affects all of us. Water contamination can be accidental or intentional and the consequences are drastic unless the appropriate measures are adopted on the spot. This review provides a critical assessment of the applicability of various technologies for real-time water quality monitoring, focusing on those that have been reportedly tested in real-life scenarios. Specifically, the performance of sensors based on molecularly imprinted polymers is evaluated in detail, also giving insights into their principle of operation, stability in real on-site applications and mass production options. Such characteristics as sensing range and limit of detection are given for the most promising systems, that were verified outside of laboratory conditions. Then, novel trends of using microwave spectroscopy and chemical materials integration for achieving a higher sensitivity to and selectivity of pollutants in water are described