Very weakly coupled new-physics particles in the MeV-GeV range appear as mediators in various "portals" to a hidden sector. Their interaction with Standard Model particles is feeble and these states ...are usually long-lived, so that the experimental search fully profits of a high-intensity setup, such as that of fixed-target experiments. Within the vector portal hidden-sector model a dark photon might exist which predominantly decays to dark matter particles. A search for such an invisible particle has been performed, exploiting the efficient photon-veto capability and high resolution tracking of the NA62 detector at CERN. The signal stems from the chain K+ → π+π0 followed by the π0 decay to a photon-dark-photon pair. No significant statistical excess has been identified. Upper limits on the dark photon coupling to the ordinary photon as a function of the dark photon mass have been set.
The Physics Beyond Colliders initiative is an exploratory study aimed at exploiting the full scientific potential of the CERN's accelerator complex and scientific infrastructures through projects ...complementary to the LHC and other possible future colliders. These projects will target fundamental physics questions in modern particle physics. This document presents the status of the proposals presented in the framework of the Beyond Standard Model physics working group, and explore their physics reach and the impact that CERN could have in the next 10-20 years on the international landscape.
The measurement of BR(K+→π+νν̄) with 10% precision by the NA62 experiment requires extreme background suppression. The Small Angle Calorimeter aims to provide an efficient veto for photons flying at ...angles down to zero with respect to the kaon flight direction. The initial prototype was upgraded and tested at the Beam Test Facility of the DAΦNE Linac at Frascati. The energy resolution and the efficiency were measured and are presented.
Evidence for the generation of benzene and substituted benzenes from hydroxyl radical degradation of azo dyes with a phenylazo substitution is presented, and a probable mechanism for benzene ...generation is proposed.
Under nitrogen-limiting, secondary metabolic conditions, the white rot basidiomycete Phanerochaete chrysosporium extensively mineralized the specifically 14C-ring-labeled azo dyes 4-phenylazophenol, ...4-phenylazo-2-methoxyphenol, Disperse Yellow 3 2-(4'-acetamidophenylazo)-4-methylphenol, 4-phenylazoaniline, N,N-dimethyl-4-phenylazoaniline, Disperse Orange 3 4-(4'-nitrophenylazo)-aniline, and Solvent Yellow 14 (1-phenylazo-2-naphthol). Twelve days after addition to cultures, the dyes had been mineralized 23.1 to 48.1%. Aromatic rings with substituents such as hydroxyl, amino, acetamido, or nitro functions were mineralized to a greater extent than unsubstituted rings. Most of the dyes were degraded extensively only under nitrogen-limiting, ligninolytic conditions. However, 4-phenylazo-U-14Cphenol and 4-phenylazo-U-14C2-methoxyphenol were mineralized to a lesser extent under nitrogen-sufficient, nonligninolytic conditions as well. These results suggest that P. chrysosporium has potential applications for the cleanup of textile mill effluents and for the bioremediation of dye-contaminated soil
Lignin peroxidase (LIP) is an extracellular enzyme produced by the lignin-degrading fungus Phanerochaete chrysosporium and is involved in azo dye degradation by this organism. In this study, LiP ...oxidation of the sulfonated azo dyes 4-(4'-sulfophenylazo)-2,6-dimethylphenol (I), Orange II 1-(4'-sulfophenylazo)-2-naphthol (II), a dimethyl analog of Orange II 1-(2',6'-dimethyl-4'-sulfophenylazo)-2-naphthol (III), and 4-(4'-sulfonamidophenylazo)-2,6-dimethylphenol (IV) was examined. Azo dye I was oxidized to 2,6-dimethyl-1,4-benzoquinone and 4-sulfophenyl hydroperoxide. Orange II (II) was oxidized to 1,2-naphthoquinone and 4-sulfophenyl hydroperoxide. The dimethyl analog of Orange II (III) was oxidized to 1,2-naphthoquinone and 2,6-dimethyl-4-sulfophenyl hydroperoxide. Azo dye IV was oxidized predominantly to 2,6-dimethyl-1,4-benzoquinone and another product, tentatively characterized as 4-sulfonamidophenyl hydroperoxide. In the 18O-labeling studies with 18O2, oxygen incorporation into the phenyl hydroperoxides from the oxidation of I and III was observed. A mechanism for azo dye degradation consistent with product identification and the 18O-labeling studies is proposed. Two successive one-electron oxidations of the phenolic ring of an azo dye by the H2O2-oxidized forms of LiP produces a carbonium ion. Then water attacks the phenolic carbon bearing the azo linkage, producing an unstable hydroxy intermediate which breaks down to yield a quinone and a sulfo- or sulfonamidophenyldiazene. The phenyldiazene is oxidized by O2 to generate the corresponding phenyldiazene radical, which eliminates N2 to yield a sulfo- or sulfonamidophenyl radical. O2 scavenges the latter to yield the corresponding hydroperoxide. This is the first report on the production and identification of a phenyl hydroperoxide in any chemical or biological system.
The branching ratio (BR) for the decay K+ → π+ν is a sensitive probe for new physics. The NA62 experiment at the CERN SPS will measure this BR to within about 10 . To reject the background from ...dominant kaon decays with final state photons, the large-angle photon vetoes (LAVs) must detect photons of energy as low as 200 MeV with an inefficiency of less than 10−4. The LAV detectors make use of lead glass blocks recycled from the OPAL electromagnetic calorimeter barrel. We describe the mechanical design and challenges faced during construction, the characterization of the lead glass blocks and solutions adopted for monitoring their performance, and the development of front-end electronics to allow simultaneous time and energy measurements over an extended dynamic range using the time-over-threshold technique. Our results are based on test-beam data and are reproduced by a detailed Monte Carlo simulation that includes the readout chain.
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