Yu. Andreev

The current most stringent constraints for the existence of sub-GeV dark matter coupling to Standard Model via a massive vector boson A′ were set by the NA64 experiment for the mass region mA′≲250 MeV, by analyzing data from the interaction of 2.84×1011 100-GeV electrons with an active thick target and searching for missing-energy events. In this work, by including A′ production via secondary positron annihilation with atomic electrons, we extend these limits in the 200–300 MeV region by almost an order of magnitude, touching for the first time the dark matter relic density constrained parameter combinations. Our new results demonstrate the power of the resonant annihilation process in missing energy dark-matter searches, paving the road to future dedicated e+ beam efforts.Received 16 August 2021Accepted 15 October 2021DOI:https://doi.org/10.1103/PhysRevD.104.L091701Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by SCOAP3.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasDark matterExtensions of gauge sectorParticle dark matterPhysical SystemsPositronsTechniquesElectromagnetic calorimetersParticle productionParticles & Fields

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, $e^- Z \to e^- Z X$, followed by its invisible decay in the NA64 experiment at CERN. No evidence for such process was found in the full NA64 data set of $2.84\times 10^{11}$ 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 $a_e$, $|\Delta a_{X}| \lesssim 10^{-15} - 10^{-13}$ for the $X$ mass region $m_X\lesssim 1$ 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.

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.

This chapter of the "Flavor in the era of LHC" workshop report discusses flavor-related issues in the production and decays of heavy states at the LHC at high momentum transfer Q, both from the experimental and the theoretical perspective. We review top quark physics, and discuss the flavor aspects of several extensions of the standard model, such as supersymmetry, little Higgs models or models with extra dimensions. This includes discovery aspects, as well as the measurement of several properties of these heavy states. We also present publicly available computational tools related to this topic.

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^{'}}.

The extension of Standard Model made by inclusion of additional $U(1)$ gauge ${L}_{\ensuremath{\mu}}\ensuremath{-}{L}_{\ensuremath{\tau}}$ symmetry can explain the difference between the measured and the predicted value of the muon magnetic moment and solve the tension in $B$ meson decays. This model predicts the existence of a new, light ${Z}^{\ensuremath{'}}$ vector boson, predominantly coupled to second and third generation leptons, whose interaction with electrons is due to a loop mechanism involving muons and taus. In this work, we present a rigorous evaluation of the upper limits in the ${Z}^{\ensuremath{'}}$ parameter space, obtained from the analysis of the data collected by the NA64-$e$ experiment at CERN SPS, that performed a search for light dark matter with $2.84\ifmmode\times\else\texttimes\fi{}{10}^{11}$ electrons impinging with 100 GeV on an active thick target. The resulting limits touch the muon $g\ensuremath{-}2$ preferred band for values of the ${Z}^{\ensuremath{'}}$ mass of order of 1 MeV, while the sensitivity projections for the future high-statistics NA64-$e$ runs demonstrate the power of the electrons/positron beam approach in this theoretical scenario.

The second harmonic of CO2 laser radiation was generated for the first time in ZnGeP2 single crystals under phase-matching conditions when the pump (fundamental-frequency) radiation was tuned within the ranges 9.19–9.7 and 10.15–10.8 μ. A study was made of the spectral, angular, and temperature widths of the phase-matching curve, of the dependence of the efficiency of conversion to the second harmonic on the pump wavelength and temperature of a crystal, and of the rate of reduction in the phase-matching angle as a result of heating.

We report the results of a search for a new vector boson ( A' ) decaying into two dark matter particles χ1χ2 of different mass. The heavier χ2 particle subsequently decays to χ1 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'→χχ¯ and axion-like or pseudo-scalar particles a→γγ . 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 me up to 390 MeV and mixing parameter ε between 3×10-5 and 2×10-2 .

We report the results of a search for a light pseudoscalar particle $a$ that couples to electrons and decays to $e^+e^-$ performed using the high-energy CERN SPS H4 electron beam. If such pseudoscalar with a mass $\simeq 17$ MeV exists, it could explain the ATOMKI anomaly. We used the NA64 data samples collected in the "visible mode" configuration with total statistics corresponding to $8.4\times 10^{10}$ electrons on target (EOT) in 2017 and 2018. In order to increase sensitivity to small coupling parameter $\epsilon$ we used also the data collected in 2016-2018 in the "invisible mode" configuration of NA64 with a total statistics corresponding to $2.84\times 10^{11}$ EOT. A thorough analysis of both these data samples in the sense of background and efficiency estimations was already performed and reported in our previous papers devoted to the search for light vector particles and axion-like particles (ALP). In this work we recalculate the signal yields, which are different due to different cross section and life time of a pseudoscalar particle $a$, and perform a new statistical analysis. As a result, the region of the two dimensional parameter space $m_a - \epsilon$ in the mass range from 1 to 17.1 MeV is excluded. At the mass of the ATOMKI anomaly the values of $\epsilon$ in the range $2.1 \times 10^{-4} < \epsilon < 3.2 \times 10^{-4}$ are excluded.

Efficient (49 ± 5%) second harmonic generation was demonstrated for the first time in the infrared. The frequency of CO2 laser radiation with a pulse duration of ~2 nsec and an intensity of up to 1GW/cm2 was doubled in an unbleached ZnGeP2 crystal. The internal energy efficiency was ∼80%.

We present measurements of the reduction of light output by plastic scintillators irradiated in the CMS detector during the 8 TeV run of the Large Hadron Collider and show that they indicate a strong dose rate effect. The damage for a given dose is larger for lower dose rate exposures. The results agree with previous measurements of dose rate effects, but are stronger due to the very low dose rates probed. We show that the scaling with dose rate is consistent with that expected from diffusion effects.

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 X17 boson. So far, the search for the decay X17→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 X17 parameter space. If a signal-like event is detected, an unambiguous observation is achieved by reconstructing the invariant mass of the X17 decay with the proposed method. To reach this goal an optimization of the X17 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 on a search for a new $Z'$ ($L_\mu-L_\tau$) vector boson 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. A signal event is 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 statistic of $(1.98\pm0.02)\times10^{10}$ muons on target, no event is observed in the expected signal region. This allows us to set new limits on part of the remaining $(m_{Z'},\ g_{Z'})$ parameter space which could provide an explanation for the muon $(g-2)_\mu$ 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.

The inclusion of an additional U(1) gauge $L_{\mu} - L_{\tau}$ symmetry would release the tension between the measured and the predicted value of the anomalous muon magnetic moment: this paradigm assumes the existence of a new, light $Z'$ vector boson, with dominant coupling to ${\mu}$ and ${\tau}$ and interacting with electrons via a loop mechanism. The $L_{\mu} - L_{\tau}$ model can also explain the Dark Matter relic abundance, by assuming that the $Z'$ boson acts as a "portal" to a new Dark Sector of particles in Nature, not charged under known interactions. In this work we present the results of the $Z'$ search performed by the NA64-$e$ experiment at CERN SPS, that collected $ \sim 9 \times 10^{11}$ 100-GeV electrons impinging on an active thick target. Despite the suppressed $Z'$ production yield with an electron beam, the limits sets by NA64-$e$ are competitive with other experimental searches, and partially exclude the $g-2$ preferred model parameter values for $Z'$ masses lighter than 2 MeV. This result proves the complementarity of this search with NA64-${\mu}$, the parallel effort of the NA64 collaboration with a muon beam.

Phase-matching conditions are considered for second harmonic generation (SHG) and optical parametric generation in LiGa(S1−xSex)2 mixed crystals as a function of chemical composition under the supposition of linear dependence of refractive indices on x. It has been shown that by tuning x over the range 0–1 the SHG can be realized in XY plane for λ=2.1–7.8μm pumping at ϕ=43–90°, in YZ plane for λ=2.1–2.2 and 4.8–7.8 μm pumping at θ=0–90°, and in XZ plane for λ=1.6–11.7μm pumping at θ=0–57°. The LiGa(S1−xSex)2 solid solutions are also attractive for design of tunable femtosecond pulse frequency converters with saving of pump pulse duration.

The QCD effects are shown to result at smw2 ⪌ 1 in a considerable increase of the νN cross section and modification of dσdy in comparison with scaling. At smw2 ≈ 3 × 103 the QCD cross section is twice that of scaling. At smw2 ⪌ 1 the QCD structure functions of the nucleon acquire effective scaling behaviour.

For the first time broadband sum frequency generation in ZnGeP2 crystal has been accomplished with a compact cryogenic slab RF discharge CO laser. The spectrum of the CO laser operating in a repetitively pulsed multiline Q-switching mode consisted of ~90 emission lines in the wavelength range of 4.95–6.60 µm. Internal sum frequency generation efficiency was reached up to 8.2%. The resulted spectrum contained ~200 spectral lines in the wavelength range of 2.5–3.2 µm.

Broadband three-stage frequency conversion of multiline sub-microsecond CO laser radiation in a single sample of ZnGeP2 crystal was experimentally and numerically studied for the first time, to the best of our knowledge. As a result, the hybrid laser system emitted more than 200 narrow spectral lines within the 2.4&#x2013;6.2&#x00A0;&#x03BC;m spectral range. The measured conversion efficiencies of the first, second, and third stages were about 4.8%, 0.4%, and 0.05%, respectively. Our numerical simulation demonstrated that the third stage of this frequency conversion can extend the laser system spectrum toward the shorter wavelength of 2.2&#x00A0;&#x03BC;m.

We report the method and results of a complex analysis of phase-matching and nonlinear properties for biaxial crystals of all point groups of symmetry, which determine their functional possibilities in solving various problems of nonlinear frequency conversion of laser radiation.

We study a possibility to detect sleptons at post-WMAP benchmark points at LHC(CMS). We find that at $L_{tot}=30 fb^{-1}$ it would be possible to detect sleptons at points A, B, C, D, G. We also investigate the production and decays of right and left sleptons separately. We find that at $L_{tot}=30 fb^{-1}$ it would be possible to detect right sleptons with a mass up to 200 GeV and left ones with a mass up to 300 GeV.

We studied performances of two SiPMs before and after irradiation at the Lubljana reactor. These high density (15 μ m cell pitch size) SiPMs were developed by Hamamatsu (in cooperation with the CMS SiPM group) for the CMS HCAL Upgrade Phase I project. The S10943-4732 is a photosensor selected for the CMS HE HCAL where the SiPMs will be exposed to 2× 1011 n/cm2 (1 MeV equivalent) for the operation time of the SLHC (integrated luminosity—5000 fb−1). The HD-1015CN SiPM was developed using new Hamamatsu trench technology to reduce optical cross-talk (X-talk) between SiPM cells. Both SiPMs are considered as candidates for the CMS HCAL barrel upgrade. The SiPMs were irradiated with reactor neutrons up to 1 MeV equivalent fluence of 2× 1012 n/cm2 (that corresponds to the maximum integrated neutron fluence in the HCAL barrel for the duration of the SLHC operation).

Dispersion of refractive index and absorption coefficients in flux-grown high-resistivity KTiOPO4 crystals between 0.2–2.5 THz are verified at room temperature by a THz-TDS. Measured dispersion components nx, ny and nz are approximated for the first time in the form of Sellmeier equations. Phase matching for down-conversion into the THz range under a visible and near IR pump is found possible only in the principle plane by and types of three-wave interactions. Low frequency THz generation is favorable due to the low absorption coefficient down to 0.2 cm−1, below 0.5 THz.

Monoclinic and cubic Ga2S3 crystals were obtained by Bridgman and flux methods. For the first time optical properties are measured in the bulk samples including THz range. The transparency range 0.44–25 μm is recorded. Ga2S3 crystal demonstrated 20 times higher light induced damage threshold compared to GaSe. No phonon absorption peaks are found in the THz range at wavenumbers below 100 cm−1. IR and THz optical, as well as other physical properties render Ga2S3 among the prospective materials for THz applications.

A study was made of second-harmonic generation in a high-quality ZnGeP2 crystal (absorption coefficient 0.1 cm−1 ) . The second-harmonic power ranged from 2.45 to 4 mW when the CO laser power was 81.25–194 mW. The maximum external efficiency of second-harmonic generation reached 3%.

Frequency doubling of the radiation of selective and nonselective carbon monoxide lasers in nonlinear ZnGeP&lt;sub&gt;2&lt;/sub&gt;and GaSe crystals has been experimentally investigated. An internal frequency-conversion efficiency as high as 7% has been obtained, with enrichment of the spectrum of the converted frequencies due to the parallel process of sum-frequency generation. The possibility is discussed of using the methods of nonlinear crystal optics to create a broad-range coherent-radiation source in the mid-IR and terahertz ranges of the spectrum, based on carbon monoxide lasers.

The method and results of the analysis of phase-matching and nonlinear properties for all point groups of symmetry of uniaxial crystals that determine their functional possibilities for solving various problems of nonlinear frequency conversion of laser radiation are presented.

We present the measurement of the intrinsic hadronic contamination at the CERN SPS H4 beamline configured to transport electrons and positrons at 100 GeV/c. The analysis, performed using data collected by the NA64-e experiment in 2022, is based on calorimetric measurements, exploiting the different interaction mechanisms of electrons and hadrons in the NA64 detector. We determined the contamination by comparing the results obtained using the nominal electron/positron beamline configuration with those from a dedicated setup, in which only hadrons impinged on the detector. We also obtained an estimate of the relative protons, anti-protons and pions yield by exploiting the different absorption probabilities of these particles in matter. We cross-checked our results with a dedicated Monte Carlo simulation for the hadron production at the primary T2 target, finding a good agreement with the experimental measurements.

The frequencies of CO2 and CO lasers were summed in a ZnGeP2 crystal as a result of a type I three-frequency interaction: the phase-matching angle was θpm =56° and the angular width of the phase-matching curve was 2°50'. The output power of the sum-frequency radiation was ∼0.6 mW.

Results from a study of the radiation hardness of silicon photomultipliers (SiPMs) are presented. New ultra high density SiPMs have been recently developed by FBK for the CMS HCAL Barrel phase I upgrade. SiPMs were irradiated to a total dose of 2×1012n∕cm2 (1 MeV equivalent) at the TRIGA reactor at the JSI in Slovenia. The SiPM’s main parameters were measured before and after irradiation. The effects of the neutron radiation on breakdown voltage, signal amplitude, dark current and noise for these devices are shown and discussed.

The anisotropy of optical properties of high quality beta barium borate crystal (β-BaB2O4, β-BBO) was studied in the main transparency window by using classic spectroscopic methods and in the range of 0.2 – 2 THz by using THz time-domain spectroscopy. β-BBO crystals were grown by the top-seeded solution technique in a highly resistive furnace with a heat field of 3-fold axis symmetry. At room temperature (RT), absorption coefficient in the maximal transparency window in grown crystals did not exceed 0.05 cm-1. Strong absorption anisotropy was observed in 3 – 5 μm and the THz range. At 1 THz absorption coefficients for e and o wave were, respectively, 7 cm-1 and 21 cm-1 at RT; 2 cm-1 and 10 cm-1 at 81 K. At the most attractive for out-of-door applications range < 0.4 THz the absorption coefficient is found to be very low: below 0.2 cm-1 at RT and 1 cm-1 at 81 K. Refractive indices dispersions measured by THz-TDS were approximated in the form of Sellmeier equations. Birefringence is found quite large for phase matched difference frequency generation (DFG) or down-conversion into the THz range (THz-DFG) under near IR pump at RT and 81 K. Type II (oe-o and eo-o), and type I (ee-e) three wave interactions can be realized at RT. THz-DFG of Nd:YAG laser and KTP OPO can be realized by type II (oe-o) three-wave interaction. For selected spectral ranges of femtosecond Ti:Sapphire laser efficient phase matched and group velocity matched optical rectification can be realized by another two types of three wave interactions. Accounting other well-known attractive physical properties of β-BBO crystal, wide application in THz technique can be forecasted.

The frequency conversion of Ti:Sapphire laser second harmonic pulses into two-color emission using a tandem of BaWO4 Raman crystals was experimentally demonstrated with an internal efficiency of ∼17%. The output emission contained symmetrical Stokes and anti-Stokes spectral components separated by 902 cm−1 with a full-width half-maximum bandwidth of ≥110 cm−1 each. The applicability of this two-color emission was numerically verified for the production of longwave infrared ultrashort pulses suitable for seeding a high-pressure CO2 laser amplifier via difference frequency generation in LiGaS2 crystal.

An experimental investigation was made of cascade generation of the fourth harmonic of CO2 laser radiation and of the second harmonic of CO laser radiation in single crystals of zinc germanium diphosphide. The radiation was converted to the spectral range 2.3–3.1 μ. The overall efficiency of conversion of CO2 laser radiation to the fourth harmonic was ∼ 0.1 %, but it should be possible to increase it to 20%. The efficiency of conversion of CO laser radiation to the second harmonic was (2.5–10)×10−3%.

The LHC (CMS) discovery potential in the search for supersymmetry and lepton-flavor violation in neutralino decays using the e ± µ∓ + E T miss signature is studied. A detailed study is done for the CMS test points LM1-LM9. It is shown that, for the point LM1, it is possible to detect lepton-flavor violation in neutralino decays with lepton-flavor-violating branching Br( $$\tilde \chi _2^0 $$ → µ± e ∓ $$\tilde \chi _1^0 $$ ) ≥ 0.04 Br( $$\tilde \chi _2^0 $$ → e + e − $$\tilde \chi _1^0 $$ , µ+ µ− $$\tilde \chi _1^0 $$ ) for an integral luminosity of 10 fb−1. The discovery potential in the mSUGRA-SUSY scenario with tan β = 10, sgn(µ) = + in the (m 0, m 1/2) plane using the e ± µ∓ + E T miss signature is determined.

The PMTs of the CMS Hadron Forward calorimeter were found to generate a large size signal when their windows were traversed by energetic charged particles. This signal, which is due to Čerenkov light production at the PMT window, could interfere with the calorimeter signal and mislead the measurements. In order to find a viable solution to this problem, the response of four different types of PMTs to muons traversing their windows at different orientations is measured at the H2 beam-line at CERN. Certain kinds of PMTs with thinner windows show significantly lower response to direct muon incidence. For the four anode PMT, a simple and powerful algorithm to identify such events and recover the PMT signal using the signals of the quadrants without window hits is also presented. For the measurement of PMT responses to Čerenkov light, the Hadron Forward calorimeter signal was mimicked by two different setups in electron beams and the PMT performances were compared with each other. Superior performance of particular PMTs was observed.

Temperature dependences of nonlinear ZnGeP2 crystal indices within the wavelength range of 5.0–6.2 μm (around noncritical spectral phase-matching) were examined with a frequency-selective Q-switched CO laser. The correct dependences were found and applied for numerical study of the spectrum tuning by the crystal temperature changing under the broadband CO laser sum frequency generation. The latter was experimentally studied for the crystal temperature range from the room one up to 145 °C. Requirements for ZnGeP2 crystal temperature changing needed for broadband frequency conversion of 5–7.5 μm radiation were formulated.

We comment on the recent paper by V.D. Antsygin et al. [Opt. Commun. 309 (2013) 333–337], in which for the first time dispersions of refractive indices nx,z in lithium triborate (LBO) were presented for the THz domain. Their claim of “nx>nz”, based on measurements by THz time-domain spectroscopy (TDS), is contrary to the well-known relationship for the maximum transparency region.

Optical properties of nonlinear PbIn6Te10 (PIT) crystal were studied for the first time within 30–1200 µm (0.2–15 THz) by FTIR and THz-TDS. It was found that PIT possesses the most attractive transparency features for efficient generation of long-wave mid-IR emission including 20–60 µm (5–15 THz) region by optical rectification. This crystal is also found useful for phase matched DFG generation into the long-wave THz region. In particular, by model study phase matched down-conversion of CO and CO2 laser lines into 130–1200 µm (0.3–2.3 THz) range is shown possible by ooe and eoe type of three wave interaction. Noncritical 90° phase matching for eoe type of interactions can be realized by selecting samples with specified composition.

The cross section for high energy muon bremsstrahlung on heavy atoms is calculated without the use of the Born approximation. It is shown that the correction to the Born approximation in the region of momentum transfers $q$ of the order of $\ensuremath{\mu}c$ has the same order of magnitude as the well-known correction of Davies, Bethe, and Maximon. It is shown also that these corrections have different signs and nearly compensate each other.

The relaxation time and absorption and emission profiles of the 0.59 THz TO phonon resonance in a ε-GaSe single crystal were measured using terahertz free induction decay, observed directly as a sequence of decaying sinusoidal oscillations in the time-domain signal following single-cycle pulse excitation. The phonon line profile was also measured using frequency-domain transmission with the resolution of 0.25 GHz and was found to be Lorentzian.

Abstract We analyse the functional capabilities of new crystals, BaGa 2 GeS 6 (BGGS) and BaGa 2 GeSe 6 (BGGSe), which are used for nonlinear optical frequency conversion in their transparency range. The wavelengths at which maximum conversion efficiencies can be obtained and the tuning range for difference-frequency generation are found. It is shown that there are wavelength combinations at which the effective nonlinearity coefficient varies only slightly in a wide frequency band.

Optical properties of nonlinear Ga <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> S <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> are studied to reveal possibility for THz applications. The results establish that 3-d (bulky) Ga <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> S <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> is a strong potential competitor to a layered GaSe and its solid solutions those possess outstanding optical properties.

A pulsed TEA CO2 laser was used in an investigation of the influence of the pump radiation parameters (mode composition, wavelength, pulse duration), of the focusing conditions, of the properties of the material (absorption coefficient), and of the operating conditions (temperature) on the efficiency of conversion to the second harmonic and on the angular dependences of phase matching in ZnGeP2 crystals. The calculated results were found to be in good agreement with the experimental data.

Long bases RT THz standoff spectrometer is designed. GaSe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">91</sub> S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.09</sub> :Al(0.03 at.%) DFG of near IR lasers was seeded by THz emission from electronic system. THz generation efficiency was improved by the factor of ≥10 at principally reduced emission bandwidth, and pulse magnitude variation decreased for at least of 4-5 times.

High optical quality GaSe samples with faces parallel and orthogonal to the optical axis are manufactured. o-and e-wave dispersions are studied by THz time domain spectroscopy. New dispersion equations are designed that are suitable for application in the entire transparency range from the near IR through the mid-IR and further into the THz.

Terahertz spectrometer up to 110 m single-pass measurement trace was realized by room-temperature GaSe:S down-converter operating at 0.2-0.6 THz range with 0.1 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> high resolution. Ab-initio measurements were carried out in the real atmosphere.

The second harmonic of radiation from a molecular NH3 laser was generated for the first time in CdGeAs2 single crystals. The internal efficiency of the frequency doubling reached 5% for radiation at the wavelength of 11.7 μ, when the efficiency of conversion of CO2 laser radiation power (used for direct optical pumping of the NH3 laser) into 6-μ radiation was highest.

In this study, we present the measurement of the intrinsic hadronic contamination at the CERN SPS H4 beamline configured to transport electrons and positrons at 100 GeV/c momentum. The analysis was performed using data collected by the NA64-$e$ experiment in 2022. Our study is based on calorimetric measurements, exploiting the different interaction mechanisms of electrons and hadrons in the NA64-ECAL and NA64-HCAL detectors. We determined the intrinsic hadronic contamination by comparing the results obtained using the nominal electron/positron beamline configuration with those obtained in a dedicated setup, in which only hadrons impinged on the detector. The significant differences in the experimental signatures of electrons and hadrons motivated our approach, resulting in a small and well-controlled systematic uncertainty for the measurement. Our study allowed us to precisely determine the intrinsic hadronic contamination, which represents a crucial parameter for the NA64 experiment in which the hadron contaminants may result in non-trivial backgrounds. Moreover, we performed dedicated Monte Carlo simulations for the hadron production induced by the primary T2 target. We found a good agreement between measurements and simulation results, confirming the validity of the applied methodology and our evaluation of the intrinsic hadronic contamination.

Thermal dark matter models with particle $\chi$ 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 $\chi$ 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 $9.37\times10^{11}$ 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 $m_{A'} \lesssim 0.35$ GeV, and to exclude scalar and Majorana dark matter with the $\chi-A'$ coupling $\alpha_D \leq 0.1$ for masses $0.001 \lesssim m_\chi \lesssim 0.1$ GeV and $3m_\chi \leq m_{A'}$.

We present the results of a missing-energy search for Light Dark Matter which has a new interaction with ordinary matter transmitted by a vector boson, called dark photon $A^\prime$. For the first time, this search is performed with a positron beam by using the significantly enhanced production of $A^\prime$ in the resonant annihilation of positrons with atomic electrons of the target nuclei, followed by the invisible decay of $A^\prime$ into dark matter. No events were found in the signal region with $(10.1 \pm 0.1)~\times~10^{9}$ positrons on target with 100 GeV energy. This allowed us to set new exclusion limits that, relative to the collected statistics, prove the power of this experimental technique. This measurement is a crucial first step toward a future exploration program with positron beams, whose estimated sensitivity is here presented.

The first search for a heavy charged vector boson in the final state with a tau lepton and a neutrino is reported, using 19.7 fb−1 of LHC data at s=8TeV. A signal would appear as an excess of events with high transverse mass, where the standard model background is low. No excess is observed. Limits are set on a model in which the W′ decays preferentially to fermions of the third generation. These results substantially extend previous constraints on this model. Masses below 2.0 to 2.7 TeV are excluded, depending on the model parameters. In addition, the existence of a W′ boson with universal fermion couplings is excluded at 95% confidence level, for W′ masses below 2.7 TeV. For further reinterpretation a model-independent limit on potential signals for various transverse mass thresholds is also presented.

We have succeeded in generating the second harmonic of the radiation from a DF laser for the first time, using single crystals of ZnGeP2. For crystals with lengths of 10.1 and 13.6 mm, the overall external efficiencies of the entire oscillator system were 4 and 6.2%. The internal efficiencies of second-harmonic generation in the crystals were 7.6 and 11.8%, respectively.

Frequency conversion of nontraditional CO2 laser radiation bands was performed for the first time. The second harmonic of the 4.3μ (1001–1000) band was generated and this was summed with the second sequence band at 10.4μ (0002-1001). The phase matching angles were 55°50' and 54°20', respectively. The spectral and angular phase-matching bandwidths were investigated. The efficiency of doubling of the P(26) line in the 4.3μ band by conversion in a ZnGeP single crystal exceeded 10%.

A search for transient point sources of ultra-high-energy (UHE) γ-rays has been performed, based on the correlation of two extensive air shower arrays, BAKSAN (North Caucasus, 1700 m a.s.l., BAKSAN Neutrino Observatory, Russia) and EAS-TOP (Campo Imperatore, 2005 a.s.l., Laboratori Nazionali del Gran Sasso, Italy), which are located at very similar latitudes (φ≈43° N), and separated in longitude by Δλ≈33.7°. The search has been conducted at primary energy Eγ⩾5×1013 eV on the time scale of a daily source transit over the sky, observable in the northern hemisphere (19°<δ<69°), and for three sources, namely the Crab Nebula, Markarian 421 and Markarian 501, observed at TeV energies by atmospheric Cherenkov detectors. The stability of the single detectors has been studied and verified up to high significance level. No coincident excess, not compatible with the expectations from statistical fluctuations, has been observed. The obtained upper limits to the rate of transient events, nγ, at 90% c.l., are concerning the sky survey, in the declination band corresponding to the zenith, nγ/(Ωt)<12/(yr sr) with Φγ(Eγ>5×1013 eV)>2.0×10−11 cm−2s−1 and duration Δt<8 h; concerning the candidate sources, e.g., for Markarian 421: nγ/t<7.7/yr with Φγ(Eγ>5×1013 eV)>1.3×10−11 cm−2s−1 and Δt<7.5 h. A coincident episode from Markarian 421, observed on 15 January, 1994, with expected chance imitation rate nch= 0.01 is discussed.

A cheap, fire- and explosion-protected Microwave Sensor Level Meter (MSLM) was developed for controlling natural and waste water up to 100-m depth. The device is a network device. There is an opportunity to connect up to 256 devices to the total information system. The MSLM may be used to control a dry waste reservoir filling including those with slightly contrasting boundaries such as those paper and plastic waste have. There is a possibility to use it in industry to measure a level of reservoir filling with dry and liquid substances as well as a level of filling with water reservoirs which are initially filled with dry substances.

We study the Minimal Supersymmetric Standard Model (MSSM) with large gluino mass [Formula: see text]. In particular, we discuss the LHC supersymmetry discovery signatures with [Formula: see text], n ≥ 0 for the MSSM with large gluino mass. We show that for some relations among squark and neutralino masses leptonic signatures with [Formula: see text], n ≥ 1 do not allow to discover supersymmetry at the LHC and the only supersymmetry discovery signature is the signature with no [Formula: see text]. Moreover, for LSP mass close to squark masses the LHC discovery potential for this signature is strongly reduced.

We study the light output, light collection efficiency and signal timing of a variety of organic scintillators that are being considered for the upgrade of the hadronic calorimeter of the CMS detector. The experimental data are collected at the H2 test-beam area at CERN, using a 150 GeV muon beam. In particular, we investigate the usage of over-doped and green-emitting plastic scintillators, two solutions that have not been extensively considered. We present a study of the energy distribution in plastic-scintillator tiles, the hit efficiency as a function of the hit position, and a study of the signal timing for blue and green scintillators.

Lithium triborate LiB3O5 (LBO) crystals are widely used for frequency conversion of the near-IR lasers within main transparency windows. Their optical properties at these wavelengths are well studied. However, very little work has been published on the properties in the terahertz (THz) range. There was a lack of data on the refractive indices, the absorption coefficients spectra and their temperature dispersions. There are no reports of THz applications. Present work reveals all these topics including the prospects for use LBO crystals as down-converters of the near-IR lasers radiation. Optically finished samples of flux-grown LBO crystals were studied by THz-TDS. The refractive index dispersions were recorded and then approximated in the form of Sellmeier equations for the temperatures of 300 and 81 K. The phase-matching curves for the IR-THz and THz-THz frequency conversions were calculated. It was found that the absorption coefficients of LBO decrease significantly with cooling to cryogenic temperatures, but the overall character of optical properties changes is intricated. Experimental results are discussed in detail considering potential characteristics of THz down-converters.

Optical properties of β -BBO crystals i. e. absorption coefficient and refractive index dispersions, were studied using a custom-made terahertz time-domain spectrometer (THz-TDS) in the range of 0.2-2.0 THz at the room temperature (RT) of 293 K and at liquid nitrogen (LN) temperature of 81 K. The measured ordinary and extraordinary wave refractive indices were approximated in the form of Sellmeier equations. Phase-matching conditions for the IR- THz and THz- THz frequency conversion were calculated.

Abstract We present the thorough studies of optical properties of BiB 3 O 6 (BIBO) crystal in the millimeter-wave (subterahertz) range. We observe a large birefringence Δn = n Z -n X = 1.5 and the values of absorption coefficients of all three axes to be less than 0.5 cm −1 at the frequency of 0.3 THz. The difference from visible range in angle ϕ between the dielectric axis z and crystallophysical axis X is found to be more than 6°. The simulated phase-matching curves in the xz plane of the crystal show the optimal value of the angle θ to be around 25.5°±1° for an efficient millimeter-wave generation under the pump of 1064 nm laser radiation.

GaSe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> crystals were used for long-wave mid-IR generation by KTP OPO down-conversion. Optimal composition GaSe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> , shown 6 times higher efficiency than that of GaSe. Significant structure strengthening was achieved with Al-doping.

A dense set of solid solution crystals GaSe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> is examined using THz-TDS. Evolution of phonon absorption peaks with the increase of S content is shown to have complex transformation, which should be considered in the design of dispersion equations for THz applications.

Abstract The thermo-optic coupling process of second harmonic generation was numerically simulated in ZnGeP 2 crystals pumped by a pulsed CO 2 laser at the wavelength of 9.6 μm, under the strong and weak cooling conditions. The conversion efficiencies, temperature distributions were calculated during the evolution of the thermo-optic coupling. The results showed that the thermooptic coupling was weak in the strong cooling condition, which nearly did not disturb the conversion processes and temperature distribution, while in the weak cooling case, the temperature distribution showed a great influence on the conversion efficiency and light intensity. Finally, it was found that compensation of the phase mismatch induced by the thermal effect can well recover the conversion efficiency.

As the author writes this in Kiev in March, he can imagine what life will be like on April 26, 1996. The streets of Ukrainian cities will be decorated with flags of mourning to commemorate the tenth anniversary of the accident at the Chernobyl Nuclear Power Station. On this day, Ukrainians will drink vodka without clinking their glasses together. They will remember once again the day that split their lives in two: They now measure time {open_quotes}before Chernobyl{close_quotes} and {open_quotes}after Chernobyl,{close_quotes} in the same way an older generation measures life {open_quotes}before the war{close_quotes} and {open_quotes}after the war.{close_quotes} It is still so much easier to immortalize the names of those who perished than to provide for the living. There are liquidation workers who literally saved the world from the Chernobyl disaster at the cost of their own lives. Inhabitants of the Chernobyl zone, and children who in the past 10 years have been exposed to monstrous levels of radiation. Unfortunately, the government remembers them only on anniversaries. Most of the men the author interviewed have been silent for 10 years - not because they were scared to talk about what happened at Chernobyl, but because no one wanted to listen. And,more » to be honest, they have been more concerned with how to survive and how to provide for their families in these complicated times. The author interviewed many of them in their apartments. He was struck by the fact that their homes were all decorated `Chernobyl style,` that is, in a somewhat provincial fashion. More striking still was the fact those who suffered the most from the explosion at the nuclear power station were convinced that it should not be shut down.« less

We launched into a development of a new stand-off sensing system that can detect atmospheric and hazardous gases in real atmosphere utilizing THz technology. Narrow line width, &lt;0.1 cm^-1, long-wave (mid-IR and THz) source based on difference frequency generation (DFG) in collinear configuration in GaSe_0.91S_0.09:Al(0.03 at. %) using seeded YAG laser and KTP OPO as pump sources was designed. The low optical loss coefficient and large hardness, together with the simplicity of the processing, make GaSe_0.91S_0.09:Al(0.03 at. %) as a high-reliable and effective THz-wave generator suitable for out-of-door application. We demonstrate incoherent terahertz wave detection by stand-off room temperature Schottky diodes located at over 110 m using open waveguide formed by multitude HPE lenses, mirrors and/or unpolished reflectors.

The Phase I upgrade of the CMS Hadron Endcap Calorimeters consists of new photodetectors (Silicon Photomultipliers in place of Hybrid Photo-Diodes) and front-end electronics. The upgrade will eliminate the noise and the calibration drift of the Hybrid Photo-Diodes and enable the mitigation of the radiation damage of the scintillators and the wavelength shifting fibers with a larger spectral acceptance of the Silicon Photomultipliers. The upgrade also includes increased longitudinal segmentation of the calorimeter readout, which allows pile-up mitigation and recalibration due to depth-dependent radiation damage. As a realistic operational test, the responses of the Hadron Endcap Calorimeter wedges were calibrated with a 60Co radioactive source with upgrade electronics. The test successfully established the procedure for future source calibrations of the Hadron Endcap Calorimeters. Here we describe the instrumentation details and the operational experiences related to the sourcing test.

Комплексная оценка качества древесины сосны в географических культурах Архангельской области

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 3.22e11 electrons on target collected during 2016-2021 runs no signal events were found. This allows to derive new constraints on the $Z'-e$ coupling strength, which for the mass range $0.3 &lt; m_{Z'} &lt; 100$ MeV are more stringent compared to those obtained from the neutrino-electron scattering data.

We introduce the notion of the difference quotient set of a real valued function $f$ on a set $E\subset[0,1]$, and compare this set to the range of $f$ on $E$. We discuss the measure theoretic properties of both the range and the difference quotient set of $f$ over $E$ under different assumptions on $f$ and $E$.

Optical properties of β-BBO were studied in the range of 0.2 – 2.5 THz at RT and 81 K by THz–TDS. Recorded dispersions were approximated in the form of Sellmeier equations. Phasematched down-conversion, as well as SHG within the THz range, are found possible. Efficient optical rectification into long wavelength region was experimentally observed.

The spectrum of sum frequency generation when converting multiline CO laser radiation in ZnGeP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> under noncritical spectral phase-matching was thoroughly studied. This spectrum was found to be a broadband comb of multiline groups with complicated fine substructure that is attractive for atmospheric spectroscopy.