Prospects of detecting massive isosinglet neutrino at LHC in the CMS detector

A possibility to search for a heavy isosinglet (sterile) neutrino using its decay mode $\nu_s \to l^{\pm} + 2 jets$ in the $S$ - channel production $pp \to W^* + X \to l^{\pm}\nu_s + X$ in the CMS experiment is studied. The only assumption about the heavy neutrino is its nonzero mixing with $\nu_e$ or $\nu_{\mu}$. The corresponding CMS discovery potential expressed in terms of the heavy neutrino mass and the mixing parameter between the heavy and light neutrino is determined. It is shown that the heavy neutrino with a mass up to 800 $GeV$ could be detected in CMS. We also investigate the production of the heavy neutrino $N_l$ mixed with $\nu_e$ and/or $\nu_{\mu}$ in the $SU_C(3) \otimes SU_L(2) \otimes SU_R(2)\otimes U(1)$ model through the reaction $pp \to W_R + X \to l^{\pm}N_l + X$ with the same heavy neutrino decay channel as above. We find that for $M_{W_R} < 3 TeV$ it is possible to discover the heavy neutrino with a mass up to $0.75 \cdot M_{W_R}$.Comment: 14 pages, 13 figure

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

Probing lepton flavour violation in νμ+N→τ+...\nu_{\mu} + N \to \tau + ... scattering and μ→tau\mu \to tau conversion on nucleons

We study lepton flavour-violating interactions which could result in the $\tau$-lepton production in the $\nu_{\mu}N$ scattering or in $\mu \to \tau$ conversion on nucleons at high energies. Phenomenological bounds on the strength of $\bar{\tau}\nu_{\mu}\bar{q}q^{'}$ interactions are extracted from the combined result of the NOMAD and CHORUS experiments on searching for $\nu_{\mu} - \nu_{\tau}$ oscillations. Some of these bounds supersede limits from rare decays. We also propose a ``missing energy'' type experiment searching for $\mu - \tau$ conversion on nucleons. The experiment can be performed at a present accelerator or at a future neutrino factory.Comment: 13 pages, 4 figure

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

H-theorem and Maxwell Demon in Quantum Physics

The Second Law of Thermodynamics states that temporal evolution of an isolated system occurs with non-diminishing entropy. In quantum realm, this holds for energy-isolated systems the evolution of which is described by the so-called unital quantum channel. The entropy of a system evolving in a non-unital quantum channel can, in principle, decrease. We formulate a general criterion of unitality for the evolution of a quantum system, enabling a simple and rigorous approach for finding and identifying the processes accompanied by decreasing entropy in energy-isolated systems. We discuss two examples illustrating our findings, the quantum Maxwell demon and heating-cooling process within a two-qubit system.Comment: 7 pages, 2 figures, IV International Conference on Quantum Technologie

Experimental demonstration of scalable quantum key distribution over a thousand kilometers

Secure communication over long distances is one of the major problems of modern informatics. Classical transmissions are recognized to be vulnerable to quantum computer attacks. Remarkably, the same quantum mechanics that engenders quantum computers offers guaranteed protection against such attacks via quantum key distribution (QKD). Yet, long-distance transmission is problematic since the essential signal decay in optical channels occurs at a distance of about a hundred kilometers. We propose to resolve this problem by a QKD protocol, further referred to as the Terra Quantum QKD protocol (TQ-QKD protocol). In our protocol, we use semiclassical pulses containing enough photons for random bit encoding and exploiting erbium amplifiers to retranslate photon pulses and, at the same time, ensuring that at the chosen pulse intensity only a few photons could go outside the channel even at distances of about a hundred meters. As a result, an eavesdropper will not be able to efficiently utilize the lost part of the signal. The central component of the TQ-QKD protocol is the end-to-end loss control of the fiber-optic communication line since optical losses can in principle be used by the eavesdropper to obtain the transmitted information. However, our control precision is such that if the degree of the leak is below the detectable level, then the leaking states are quantum since they contain only a few photons. Therefore, available to the eavesdropper parts of the bit encoding states representing `0' and `1' are nearly indistinguishable. Our work presents the experimental demonstration of the TQ-QKD protocol allowing quantum key distribution over 1079 kilometers. Further refining the quality of the scheme's components will expand the attainable transmission distances. This paves the way for creating a secure global QKD network in the upcoming years.Comment: 23 pages (main text: 15 pages, supplement: 8 pages), 21 figures (main text: 7 figures, supplement: 14 figures