A
bstract
The Compact Linear Collider (CLIC) is a proposed future high-luminosity linear electron-positron collider operating at three energy stages, with nominal centre-of-mass energies
s
= 380 GeV, ...1
.
5 TeV, and 3 TeV. Its aim is to explore the energy frontier, providing sensitivity to physics beyond the Standard Model (BSM) and precision measurements of Standard Model processes with an emphasis on Higgs boson and top-quark physics. The opportunities for top-quark physics at CLIC are discussed in this paper. The initial stage of operation focuses on top-quark pair production measurements, as well as the search for rare flavour-changing neutral current (FCNC) top-quark decays. It also includes a top-quark pair production threshold scan around 350 GeV which provides a precise measurement of the top-quark mass in a well-defined theoretical framework. At the higher-energy stages, studies are made of top-quark pairs produced in association with other particles. A study of t
̄
tH production including the extraction of the top Yukawa coupling is presented as well as a study of vector boson fusion (VBF) production, which gives direct access to high-energy electroweak interactions. Operation above 1 TeV leads to more highly collimated jet environments where dedicated methods are used to analyse the jet constituents. These techniques enable studies of the top-quark pair production, and hence the sensitivity to BSM physics, to be extended to higher energies. This paper also includes phenomenological interpretations that may be performed using the results from the extensive top-quark physics programme at CLIC.
A method for synthesis of nanocomposite with core–shell structure made of carbon matrices and La nanoparticles for its subsequent approbation as contrast agent in radiological studies has been ...proposed. The synthesis includes three stages, consisting of (1) preparation of few-layer graphite fragments (graphite nanoflakes, GNF) as carbon matrix support, (2) preparation of La-containing composite by impregnation of GNF nanoparticles with lanthanum nitrate solution with subsequent annealing and (3) surface graphitization of obtained product. All samples were studied by transmission electron microscopy, Raman and X-ray photoelectron spectroscopy. It was shown that the graphite shells contained from 2 to 3 carbon layers, and the La-containing phase was lanthanum carbonate.
2–3 nm Gd
2
O
3
nanoparticles deposited on carbon nanoflakes were prepared. These are new contrast agents for photon-counting computed tomography based on detectors allowing counting of separate ...photons. Contrast agents of the Gd
2
O
3
@C core–shell structure were prepared by graphitization of the surface of these particles. The Gd
2
O
3
and Gd
2
O
3
@C nanoparticles obtained, aqueous solution of Gd(NO
3
)
3
·6H
2
O, and a dispersion of 300–500 nm Gd
2
O
3
particles in gelatin were studied by photon-counting computed tomography. At equal gadolinium concentrations, the highest X-ray absorption was noted for Gd(NO
3
)
3
·6H
2
O and Gd
2
O
3
, which is associated with higher density of these samples. Carbon in the contrast agents does not affect the absorption. An algorithm was developed for semiquantitative determination of gadolinium by photon-counting computed tomography.
The scientific apparatus GAMMA-400 designed for study of electromagnetic and hadron components of cosmic rays will be launched to an elliptic orbit with the apogee of about 300 000 km and the perigee ...of about 500 km. Such a configuration of the orbit allows it to cross periodically the radiation belt and the outer part of magnetosphere. We discuss the possibility to use hybrid pixel detecters based on the Timepix chip and semiconductive sensors on board the GAMMA-400 apparatus. Due to high granularity of the sensor (pixel size is 55 mum) and possibility to measure independently an energy deposition in each pixel, such compact and lightweight detector could be a unique instrument for study of spatial, energy and time structure of electron and proton components of the radiation belt.
Hybrid semiconductor pixel detectors are considered of high interest for synchrotron applications like diffraction and imaging experiments. However, at photon energies above 30 keV, high-Z sensor ...materials have to be used due to the weak absorption of the most commonly used sensor material, for instance silicon wafers with a thickness of a few hundred μm. Besides materials like CdTe and Ge, semi-insulating, chromium compensated SI-GaAs(Cr) proves to be a promising sensor material for applications with X-rays in the mid-energy range up to ~60 keV. In this work, material characterisation of SI-GaAs(Cr) wafers by electrical measurements and synchrotron white beam topography as well as the characterization and application of pixel detector assemblies based on Medipix readout chips bump-bonded to 500 μm thick SI-GaAs(Cr) sensors are presented. The results show a very homogeneous material with high resistivity and good electrical properties of the electrons as well as a very promising imaging performance of the detector assemblies.
At present, there are two Micromegas detector production sites at the Dzhelepov Laboratory of Nuclear Problems, Joint Institute for Nuclear Research (DLNP JINR). The first site provides the ...production and testing of Micromegas chambers for the outer part of the large sectors (LM2) of the New Small Wheels for the ATLAS Muon spectrometer. It will produce and test 64 double-sided readout panels with a surface area of 3 m
2
each and 32 Micromegas chambers based on them. Component materials for all project participants are centrally delivered from CERN. The second site is for a complete production cycle and intended for the research and development of Micromegas detectors with widths reaching 60 cm.
Characterisation of a GaAs(Cr) Medipix2 hybrid pixel detector Tlustos, Lukas; Shelkov, Georgy; Tolbanov, Oleg P.
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
05/2011, Letnik:
633
Journal Article
Recenzirano
A semi-insulating GaAs(Cr) sensor of 300
μm thickness with a bulk resistivity of 10
9
Ω
cm and no guard ring structures has been bump bonded to a Medipix2 readout chip. The room temperature ...spectroscopic response of this device to fluorescence photons in the energy range from 8 to 28
keV at different sensor biases is measured and compared to the response of a reference detector with a 300
μm thick Si sensor. The measured responses show that the full volume of the GaAs(Cr) is active and indicate a charge collection efficiency of 90%. The spatial resolution if this device is 8
lp/mm.
En este trabajo la espectroscopia Raman ha sido empleada en la busqueda de evidencias del posible dano radiacional en un detector semiconductor de radiaciones de arseniuro de galio compensado con ...cromo al ser expuesto a un haz de electrones de 20 MeV. Los espectros Raman tomados antes y después de la irradiacion fueron deconvolucionados y su análisis mostraron que efectivamente en el material estaban teniendo lugar significativos procesos estimulados por la radiacion. Estos procesos conducen a la relajacion del estado tensional de la estructura, al incremento de la cristalinidad, y a la disminucion de la concentracion de portadores libres, que en el volumen estudiado de la muestra alcanza un 2.31 %. Los cambios observados deben estar relacionados con la generacion de defectos de tipo Frenkel en la subred del arsénico, y a cambios radiacionalmente estimulados en la cantidad y características de defectos preexistente de mayor complejidad. In this work, we use Raman spectroscopy to search for evidence of possible radiation damage in a chromium-compensated gallium arsenide semiconductor detector exposed to a 20 MeV electron beam. The Raman spectra measured before and after irradiation were deconvoluted, and their analysis shows that relevant processes stimulated by radiation take place in the material. These processes lead to the relaxation of the structure tensional state, the enhancement of crystallinity, and a decrease in the concentration of free carriers, which in the studied sample volume reaches 2.31 %. The observed changes could be related to the generation of new Frenkel-type defects in the arsenic sublattice, and to radiation-stimulated changes in the quantity and quality of pre-existing more complex defects.
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