Search for Dark Matter Axions with CAST-CAPP

The CAST-CAPP axion haloscope, operating at CERN inside the CAST dipole magnet, has searched for axions in the 19.74 μeV to 22.47 μeV mass range. The detection concept follows the Sikivie haloscope principle, where Dark Matter axions convert into photons within a resonator immersed in a magnetic field. The CAST-CAPP resonator is an array of four individual rectangular cavities inserted in a strong dipole magnet, phase-matched to maximize the detection sensitivity. Here we report on the data acquired for 4124 h from 2019 to 2021. Each cavity is equipped with a fast frequency tuning mechanism of 10 MHz/ min between 4.774 GHz and 5.434 GHz. In the present work, we exclude axion-photon couplings for virialized galactic axions down to g_aγγ = 8 × 10⁻¹⁴ GeV⁻¹ at the 90% confidence level. The here implemented phase-matching technique also allows for future large-scale upgrades.

Haloscopes aim at detecting axions by converting them into photons using high-quality resonant cavities, where the cavity resonance should be tuned with the unknown axion mass. Here, the authors improve exclusion limits using four phase-matched resonant cavities and a fast frequency scanning technique.

The novel Mechanical Ventilator Milano for the COVID-19 pandemic

This paper presents the Mechanical Ventilator Milano (MVM), a novel intensive therapy mechanical ventilator designed for rapid, large-scale, low-cost production for the COVID-19 pandemic. Free of moving mechanical parts and requiring only a source of compressed oxygen and medical air to operate, the MVM is designed to support the long-term invasive ventilation often required for COVID-19 patients and operates in pressure-regulated ventilation modes, which minimize the risk of furthering lung trauma. The MVM was extensively tested against ISO standards in the laboratory using a breathing simulator, with good agreement between input and measured breathing parameters and performing correctly in response to fault conditions and stability tests. The MVM has obtained Emergency Use Authorization by U.S. Food and Drug Administration (FDA) for use in healthcare settings during the COVID-19 pandemic and Health Canada Medical Device Authorization for Importation or Sale, under Interim Order for Use in Relation to COVID-19. Following these certifications, mass production is ongoing and distribution is under way in several countries. The MVM was designed, tested, prepared for certification, and mass produced in the space of a few months by a unique collaboration of respiratory healthcare professionals and experimental physicists, working with industrial partners, and is an excellent ventilator candidate for this pandemic anywhere in the world.

Micromegas for dark matter searches: CAST/IAXO & TREX-DM experiments

The most compelling candidates for Dark Matter to day are WIMPs and axions. The applicability of gasesous Time Projection Chambers (TPCs) with Micromesh Gas Structures (Micromegas) to the search of these particles is explored within this work. Both particles would produce an extremely low rate at very low energies in particle detectors. Micromegas detectors can provide both low background rates and low energy threshold, due to the high granularity, radiopurity and uniformity of the readout. Small (few cm wide) Micromegas detectors are used to image the axion-induced x-ray signal expected in the CERN Axion Solar Telescope (CAST) experiment. We show the background levels obtained in CAST and the prospects to further reduce them to the values required by the Internation Axion Observatory (IAXO). We also present TREX-DM, a scaled-up version of the Micromegas used in axion research, but this time dedicated to the low-mass WIMP detection. TREX-DM is a high-pressure Micromegas-based TPC designed to host a few hundreds of grams of light nuclei (argon or neon) with energy thresholds potentially at the level of 100 eV. The detector is described in detail, as well as the results of the commissioning and characterization phase on surface. Besides, the background model of TREX-DM is presented, along with the anticipated sensitivity of this search, which could go beyond current experimental limits.

TREX-DM: a low-background Micromegas-based TPC for low-mass WIMP detection

If Dark Matter is made of Weakly Interacting Massive Particles (WIMPs) with masses below [Formula: see text] GeV, the corresponding nuclear recoils in mainstream WIMP experiments are of energies too close, or below, the experimental threshold. Gas Time Projection Chambers (TPCs) can be operated with a variety of target elements, offer good tracking capabilities and, on account of the amplification in gas, very low thresholds are achievable. Recent advances in electronics and in novel radiopure TPC readouts, especially micro-mesh gas structure (Micromegas), are improving the scalability and low-background prospects of gaseous TPCs. Here we present TREX-DM, a prototype to test the concept of a Micromegas-based TPC to search for low-mass WIMPs. The detector is designed to host an active mass of [Formula: see text] kg of Ar at 10 bar, or alternatively [Formula: see text] kg of Ne at 10 bar, with an energy threshold below 0.4 keVee, and is fully built with radiopure materials. We will describe the detector in detail, the results from the commissioning phase on surface, as well as a preliminary background model. The anticipated sensitivity of this technique may go beyond current experimental limits for WIMPs of masses of 2-8 GeV.

Search for solar axions by the CERN axion solar telescope with 3He buffer gas: closing the hot dark matter gap

The CERN Axion Solar Telescope has finished its search for solar axions with (3)He buffer gas, covering the search range 0.64 eV ≲ ma ≲ 1.17 eV. This closes the gap to the cosmological hot dark matter limit and actually overlaps with it. From the absence of excess x rays when the magnet was pointing to the Sun we set a typical upper limit on the axion-photon coupling of gaγ ≲ 3.3 × 10(-10)  GeV(-1) at 95% C.L., with the exact value depending on the pressure setting. Future direct solar axion searches will focus on increasing the sensitivity to smaller values of gaγ, for example by the currently discussed next generation helioscope International AXion Observatory.

Search for sub-eV mass solar axions by the CERN Axion Solar Telescope with 3He buffer gas

The CERN Axion Solar Telescope (CAST) has extended its search for solar axions by using (3)He as a buffer gas. At T=1.8 K this allows for larger pressure settings and hence sensitivity to higher axion masses than our previous measurements with (4)He. With about 1 h of data taking at each of 252 different pressure settings we have scanned the axion mass range 0.39 eV≲m(a)≲0.64 eV. From the absence of excess x rays when the magnet was pointing to the Sun we set a typical upper limit on the axion-photon coupling of g(aγ)≲2.3×10(-10) GeV(-1) at 95% C.L., the exact value depending on the pressure setting. Kim-Shifman-Vainshtein-Zakharov axions are excluded at the upper end of our mass range, the first time ever for any solar axion search. In the future we will extend our search to m(a)≲1.15 eV, comfortably overlapping with cosmological hot dark matter bounds.

Acute toxicity and relationship between metabolites and ecotoxicity during the biodegradation process of non-ionic surfactants: fatty-alcohol ethoxylates, nonylphenol polyethoxylate and alkylpolyglucosides

The toxicity values of fatty-alcohol ethoxylates, nonylphenol polyethoxylate, and alkylpolyglucosides have been determined by applying assays with luminescent bacteria. Also, the relation between metabolites and ecotoxicity during the biodegradation process has been determined. The biodegradation tests were carried out according to the OECD 301 E test for ready biodegradability. In these tests a solution of the surfactant, representing the sole carbon source for the microorganisms, was tested in a mineral medium, inoculated and incubated under aerobic conditions in the dark. The toxicity of surfactants is related to their molecular structure (Quantitative Structure Activity Relationships, QSAR). For the alkylpolyglucosides, toxicity expressed as EC(50) is related with the critical micelle concentration (CMC), the hydrophilic-lipophilic balance (HLB) of the surfactant, and the hydrophobic alkyl chain (R). The results indicate that toxicity increased as the CMC decreased and as the hydrophobicity increased and R rose. For fatty-alcohol ethoxylates, parameters characteristic studied have been HLB, number of units of ethylene oxide and the alkyl chain length. Relationships found are in agreement with the fact that increasing the alkyl chain length leads to a lower EC(50), whereas increasing ethoxylation leads to a lower toxicity. An analysis of the behaviour of the toxicity and HLB again indicates that the toxicity was greater for surfactants with a smaller HLB. The evolution of the toxicity was studied over the biodegradation process, expressed as a percentage of inhibition. For all the non-ionic surfactants assayed, except for the nonylphenol polyethoxylate, a major decline was found in toxicity during the first days of the biodegradation assay and at all the concentrations tested.

Simplified spectrophotometric method using methylene blue for determining anionic surfactants: applications to the study of primary biodegradation in aerobic screening tests

In the present work, we propose a simplified spectrophotometric method for determining anionic surfactants, based on the formation of the ionic pair anionic surfactant-methylene blue (AS-MB). This method, in relation to the conventional analytic procedure, considerably reduces not only the quantity of chloroform used in extracting the ionic pair formed, but also the time and the quantity of sample necessary to perform the assay, eliminating the filtration stage. The method has been simplified by displacing the transfer equilibrium of the ionic pair AS-MB towards the organic phase, augmenting the volumetric relationship of chloroform/sample. The method proposed has been applied in the study of primary biodegradation kinetics of linear alkylbenzenesulfonate (LAS).

Kinetic and enzymatic adsorption model in a recirculation hollow-fibre bioreactor

A general procedure has been developed to model the behaviour of enzymatic reactions in a membrane bioreactor. This procedure unifies the kinetics of the reaction and the adsorption of the enzyme or enzymatic complexes on the membrane, enabling the selection of the most appropriate kinetic model. The general procedure proposed has been particularized and applied to experimental results obtained with two enzymatic reactions carried out in a hollow-fibre reactor, enzymatic hydrolysis of lactose by beta-galactosidase and glucose-fructose isomerization by glucose isomerase. The application of the general model has allowed us to determine the mechanism of the reaction for both kinetic reactions, assuming the adsorption of the enzymatic complex EGa for lactose hydrolysis and the adsorption of the free enzyme onto the membrane for glucose-fructose isomerization.

First results from the CERN axion solar telescope

Hypothetical axionlike particles with a two-photon interaction would be produced in the sun by the Primakoff process. In a laboratory magnetic field ("axion helioscope"), they would be transformed into x-rays with energies of a few keV. Using a decommissioned Large Hadron Collider test magnet, the CERN Axion Solar Telescope ran for about 6 months during 2003. The first results from the analysis of these data are presented here. No signal above background was observed, implying an upper limit to the axion-photon coupling g(agamma)<1.16x10(-10) GeV-1 at 95% C.L. for m(a) less, similar 0.02 eV. This limit, assumption-free, is comparable to the limit from stellar energy-loss arguments and considerably more restrictive than any previous experiment over a broad range of axion masses.