The CEBAF large acceptance spectrometer (CLAS) is used to study photo- and electro-induced nuclear and hadronic reactions by providing efficient detection of neutral and charged particles over a good fraction of the full solid angle. A collaboration of about 30 institutions has designed, assembled, and commissioned CLAS in Hall B at the Thomas Jefferson National Accelerator Facility. The CLAS detector is based on a novel six-coil toroidal magnet which provides a largely azimuthal field distribution. Trajectory reconstruction using drift chambers results in a momentum resolution of 0.5% at forward angles. Cherenkov counters, time-of-flight scintillators, and electromagnetic calorimeters provide good particle identification. Fast triggering and high data-acquisition rates allow operation at a luminosity of 10 34 nucleon cm −2 s −1 . These capabilities are being used in a broad experimental program to study the structure and interactions of mesons, nucleons, and nuclei using polarized and unpolarized electron and photon beams and targets. This paper is a comprehensive and general description of the design, construction and performance of CLAS.

/pdf/the-cebaf-large-acceptance-spectrometer-clas-2u9ne3shdl.pdf

The CEBAF large acceptance spectrometer (CLAS)

Silica aerogels are highly porous solid materials consisting of three-dimensional networks of silica particles and are typically obtained by removing the liquid in silica gels under supercritical conditions. Several unique attributes such as extremely low thermal conductivity and low density make silica aerogels excellent candidates in the quest for thermal insulation materials used in space missions. However, native silica aerogels are fragile at relatively low stresses. More durable aerogels with higher strength and stiffness are obtained by proper selection of silane precursors and by reinforcement with polymers. This paper first presents a brief review of the literature on methods of silica aerogel reinforcement and then discusses our recent activities in improving not only the strength but also the elastic response of polymer-reinforced silica aerogels. Several alkyl-linked bis-silanes were used in promoting flexibility of the silica networks in conjunction with polymer reinforcement by epoxy.

Tailoring Mechanical Properties of Aerogels for Aerospace Applications

The XENON100 dark matter experiment

Aerogel technology provides high added-value lightweight materials with outstanding textural properties (i.e., high surface area and open porosity). Aerogels are obtained from wet gels by using a suitable drying technology, usually supercritical drying process, able to avoid the pore collapse phenomenon in order to keep intact the porous texture of the wet material. In this sense, the study of the kinetic profile of the gel supercritical drying is regarded as a key aspect to be considered in the specific case of the design of aerogel-based systems. In this work, the drying profile with supercritical carbon dioxide (scCO 2 ) of alcogels (in ethanol) was determined using a customized supercritical fluid extraction equipment. The drying of alcogels from different precursors (inorganic-silica-, organic-starch-), densities (silica aerogel of densities 0.08 and 0.15 g/cm 3 ) and morphologies (cylindrical monoliths, microspheres) was studied. Depending on the nature of the gel precursor, the extent of drying (i.e., drying time duration) gave significant differences in the end textural properties of the dried gel.

Supercritical drying of aerogels using CO2: Effect of extraction time on the end material textural properties

The QCD vacuum shows the dynamical breaking of chiral symmetry In the hot and/or dense QCD medium, the chiral order parameter such as is expected to change as a function of temperature T and density {rho} of the medium, and its experimental detection is one of the main challenges in modern hadron physics In this paper, the theoretical expectations for the in-medium hadron spectra associated with partial restoration of chiral symmetry are discussed as well as the current status of experiments with an emphasis on the measurements of properties of mesons produced in near-ground-state nuclei

Hadron properties in the nuclear medium

Evidence forρ0Mass Modification in the3He(γ,ρ0)ppnReaction

Subthreshold ρ 0 photoproduction on 3 He

Probing theΔNNcomponent of3He

We report the design characteristics and the performance obtained with the silica aerogel Cherenkov counter recently completed for the HRS-H spectrometer of Hall A at CEBAF. Several modifications have been incorporated as a result of the prototype performance, which was reported in an earlier article. The counter meets or exceeds the original design specifications and will be used to separate pions and protons in the HRS-H spectrometer in Hall A.

Performance and design characteristics for the Hall A aerogel Cherenkov counters

The differential cross section for electron-induced neutron knockout in the reaction 4He(e,e(')n)(3)He has been measured for the first time with a statistical accuracy of 11%. The experiment was performed in quasielastic kinematics at a momentum transfer of 300 MeV/c and in the missing-momentum range of 25-70 MeV/c. The comparison of the data with theoretical calculations shows an impressive increase of the cross section resulting from final state interaction effects. Specifically, the p-n charge-exchange process dominates the cross section in this kinematical regime.

/pdf/electron-induced-neutron-knockout-from-he-4-4g39ix77ay.pdf

Electron-induced neutron knockout from He-4

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