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^{'}}.
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 2.84×1011 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.
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.
The improved results on a direct search for a new X ( 16.7 MeV ) boson that could explain the anomalous excess of e+e− pairs observed in the decays of the excited 8Be ∗ nuclei ("Berillium or X17 ...anomaly") are reported. Interestingly, new recent results in the nuclear transitions of another nucleus, 4 He , seems to support this anomaly spurring the need for an independent measurement. If the X boson exists, it could be produced in the bremsstrahlung reaction e − Z → e − Z X by a high energy beam of electrons incident on the active target in the NA64 experiment at the CERN Super Proton Synchrotron and observed through its subsequent decay into e+e− pairs. No evidence for such decays was found from the combined analysis of the data samples with total statistics corresponding to 8.4 × 1010 electrons on target collected in 2017 and 2018. This allows one to set new limits on the X−e− coupling in the range 1.2 × 10−4 ≲ ε e ≲ 6.8 × 10−4 , excluding part of the parameter space favored by the X17 anomaly, and setting new bounds on the mixing strength of photons with dark photons ( A ′ ) with a mass ≲ 24 MeV . For the 2018 run, the setup was optimized to probe the region of parameter space characterized by a large coupling ε . This allowed a significant improvement in sensitivity despite a relatively modest increase in statistics.
Successful 54 Gbit/s on–off keying (OOK) transmission over 2.2 km of multimode OM4 fibre is demonstrated. The decisive advantages of the single mode over multimode vertical cavity surface emitting ...laser (VCSEL) in transmission experiments are shown.
•Ultrasound accelerates synthesis of nanofibrillar cellulose/polystyrene composite.•High biodegradability of nanofibrillar cellulose/polystyrene composite.•High mechanic strength of nanofibrillar ...cellulose/polystyrene composite.
A new method of the synthesis of nanofibrillar cellulose/polystyrene composite based on ultrasonic treatment of styrene emulsion in cellulose-water solution was elaborated. A new approach does not require additional heating and proposes a significantly faster synthesis (15 min, 45 °C) of the target composite compared to the methods described previously. A comprehensive analysis did not reveal any significant differences between mechanical, physical and biodegradable properties of the composite obtained by ultrasonic method and that one obtained by conventional thermal method, which requires much higher temperature (above 75 °C) and reaction duration (from 3 h).
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 × 1011 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 ae,|ΔaX|≲ 10−15 –10−13 for the X mass region 1 MeV ≲ mX ≲ 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.
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. Published by the American Physical Society 2024
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