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Aerogel has been successfully used as a radiator in Cherenkov detectors. In 2004, a multilayer aerogel providing Cherenkov ring focusing was proposed and produced. FARICH (Focusing Aerogel Rich Imaging CHerenkov) detectors such as ARICH for Belle-II (KEK, Japan), Forward RICH for PANDA detector (FAIR, Germany), and FARICH for the Super Charm-Tau factory project (BINP, Novosibirsk) have been developed based on this aerogel. Prototypes of FARICH detector based on MRS APD and Philips DPC photosensors were developed and tested in the framework of this project. An angular resolution for Cherenkov rings of 3.6 mrad was achieved.

The work concerns the development of aerogel radiators for RICH detectors. Aerogel tiles with a refractive index of 1.05 were tested with a RICH prototype on the electron beam on the VEPP-4M collider. It has been shown that polishing with silk tissue yields good surface quality, the amount of light loss at this surface being about 5–7%. The Cherenkov angle resolution was measured for a tile in two conditions: with a clean exit face and with a polished exit face. The number of photons detected was 13.3 and 12.7 for the clean and polished surfaces, respectively. The Cherenkov angle resolution for the polished surface is 55% worse, which can be explained with the forward scattering on the polished surface. A tile with a crack inside was also tested. The experimental data show that the Cherenkov angle resolution is the same for tracks crossing the crack area and in a crack-free area.

Bound nuclear systems with two units of strangeness are still poorly known despite their importance for many strong interaction phenomena. Stored antiprotons beams in the GeV range represent an unparalleled factory for various hyperon-antihyperon pairs. Their outstanding large production probability in antiproton collisions will open the floodgates for a series of new studies of systems which contain two or even more units of strangeness at the PANDA experiment at FAIR. For the first time, high resolution gamma-spectroscopy of doubly strange Lambda Lambda-hypernuclei will be performed, thus complementing measurements of ground state decays of Lambda Lambda-hypernuclei at J-PARC or possible decays of particle unstable hypernuclei in heavy ion reactions. High resolution spectroscopy of multistrange Xi(-) -atoms will be feasible and even the production of Omega(-) -atoms will be within reach. The latter might open the door to the vertical bar S vertical bar = 3 world in strangeness nuclear physics, by the study of the hadronic Omega(-) -nucleus interaction. For the first time it will be possible to study the behavior of Xi(+) in nuclear systems under well controlled conditions. (C) 2016 Elsevier B.V. All rights reserved.

In 2014 the fully installed ASHIPH (Aerogel, SHifter, PHotomultiplier) system began its operation in the KEDR experiment at the VEPP-4 M e + e − -collider. The system contains 1000 liters of aerogel with refractive index n=1.05 in 160 counters that are arranged in two layers. Cherenkov light collection is preformed by means of wavelength shifters (WLS). 160 Micro-Channel Plate (MCP) PMTs with multialkali photocathode are used as photodetectors . Efficiency of relativistic particles detection was measured with e + e − → e + e − events and cosmic muons . Detection efficiency for under-threshold particles was measured with cosmic muons. From these data π / K -separation of 4σ at the momentum 1.2 GeV/c was obtained.

The excellent particle identification (PID) system is needed for the successful execution of the broad experimental program at future Super C-τ Factory (SCTF) in Novosibirsk. The main requirements for the PID system are the following: good π/K-separation in whole operational momentum range and good μ/π-separation in the momentum range from 0.4 up to 1.2 GeV/c. The RICH detector based on focusing aerogel (FARICH) could provide good π/K-separation from 0.4 GeV/c and μ/π-separation in the momentum range from 0.4 up to 1.5 GeV/c. The method FARICH is described, beam test results are presented and the status of multilayer aerogel production is given.

The Super Charm–Tau (SCT) Factory is a proposed electron–positron collider in Novosibirsk with a peak luminosity of 1 0 35 cm − 1 s − 1 operating in the energy range between 2and 6 GeV. The interaction region should be equipped by an excellent universal particle detector meeting the requirements of broad physics program of the experiment. Research and development for all detector subsystems is currently underway. Particle identification (PID) system of the detector is required to provide the state-of-the-art level of μ / π separation for the particle momenta up to 1 . 2 GeV∕c . The following options for the PID system are considered in this paper: focusing aerogel ring imaging Cherenkov (FARICH) detector composed of 4-layer aerogel tiles, threshold Cherenkov counters based on aerogel shifter photomultiplier (ASHIPH), and time-of-flight (ToF) detector combined with the time-of-propagation (ToP) approach providing a time resolution better than 30 ps . Assessment of the charged particle separation performance for these options based on simulation and prototype tests results is presented.

Aerogel for different types of Cherenkov detectors is produced by a collaboration of Budker Institute of Nuclear Physics and Boreskov Institute of Catalysis during more than two decades. So far only the production of two sizes was possible in large numbers: 50 × 50 and 115 × 115 mm 2 . This work is devoted to the development of the production technology of large scale aerogel radiators for use in the Ring-imaging Cherenkov (RICH) detectors. These detectors require additional parameters to be controlled for each aerogel tile during production. Procedures of measurement of the aerogel tiles refractive index , the light scattering length, the upper surface flatness are described.

A high performance particle identification (PID) system is essential for the successful realization of the broad physics program at the future Super C- τ Factory in Novosibirsk. The main requirements for the PID system are as follows: good π / K -separation in the entire operational momentum range and good μ ∕ π -separation in the momentum range from 0.3 to 1.2 GeV/ c . The RICH detector based on focusing aerogel radiator (FARICH) and position-sensitive photon detector meets all these requirements. The FARICH method is described, and the beam test results are presented. The FARICH system design outline for the Super C- τ Factory project is presented. Most promising photon detector options are considered.

The particle identification system ASHIPH (Aerogel, SHifter, PHotomultiplier) has been working in the KEDR experiment at VEPP-4M collider (Budker INP, Novosibirsk) since 2014. The system consists of 160 counters arranged in two layers and covers the 96% of the solid angle. Two layer system permits to use different approaches for π /K separation. Three such approaches are described. The status of the system is presented. Main system parameters such as BhaBha suppression factor, π /K separation power, relativistic particle detection efficiency were measured with help of cosmic particles and experimental data collected at the peak of J/ ψ -meson. π /K separation in the momentum range from 0.95 to 1.45 GeV/ c is better than 4 σ . Monte-Carlo simulation procedures are described and results are presented as well.

The Philips Digital Photon Counter (DPC) is a silicon photomultiplier combining Geiger-mode avalanche photodiodes (G-APD) and dedicated readout electronics in the same chip. The DPC is a promising photon sensor for future RICH detectors. A known issue of G-APD is its sensitivity to radiation damage. Two DPC sensors were tested using 800 MeV/c protons. An increase of dark counting rate with proton fluence up to 4·1011cm−2 has been measured.

Particle identification power of modern aerogel RICH detectors strongly depends on optical quality of radiators. It was shown that wavelength dependence of aerogel tile transparency after polishing cannot be described by the standard Hunt formula. The Hunt formula has been modified to describe scattering in a thin layer of silica dust on the surface of aerogel tile. Several procedures of polishing of aerogel tile have been tested. The best result has been achieved while using natural silk tissue. The resulting block has optical smooth surfaces. The measured decrease of aerogel transparency due to surface scattering is about few percent. This result could be used for production of radiators for the Focusing Aerogel RICH detectors.

Using ab initio (Hartree–Fock and local density approximation) and semiempirical (Austin Model 1) calculations, we studied the energetics and electronic structures of NB and NP complexes. We found that these complexes are electrically inactive. The formation energies are 1.6 eV for the NB coupling and 2.4 eV for the NP pairing. The N–P and N–B interatomic equilibrium distances are about 3.5 A for both complexes.

The Austin Model 1 (AM1) semi-empirical numerical method combined with the geometry optimization procedure was used to study the energetics of P–Si and P–P dimers on the Si(100)-2×1 surface in a cluster approach. It has been found that the P–Si dimers are more preferable energetically. The energy profit depends on the cluster size and is about 0.8–0.9 eV for large clusters.

The AM1 semiempirical numerical method combined with the geometry optimization procedure was used to study the energetics of active impurities (B, P) in substitutional positions at the Si(100)-2╳1 surface. It has been found that phosphorus prefers to be in the first layer (in dimers). Boron has the lowest energy in the second layer. Energy profits, counting from the fourth bulk-like layer, for B and P are 1.33 eV and 0.56 eV, respectively. Comparing of the P-Si and P-P dimers energetics has shown that P-Si dimers are more preferable energetically.

Using the local-density approximation method we have investigated a cluster model of the Al/Si(111) interface. P atoms were placed in the fifth silicon double-atomic layer (DAL) counting from the interface. The second DAL was doped with either Ga or As. The Schottky barrier height was found to be 0.75 eV at the Al/Si(intrinsic) system and 0.73 eV at the Al/Si(P-doped) case. The additional doping of the near-interface layer by Ga increased the barrier to 0.90 eV while the As doping decreased it to 0.5 eV.

A computationally inexpensive semiempirical numerical method (AM1) has been evaluated for its usefulness as a mean of providing fast estimates of geometries and energetics of defects and impurities in silicon. As a case study we considered adsorption of Al (a typical sp-bonded impurity) in the Al–Si(111) 3 × 3 system and chaotic Si and Al deposition onto the Si(100)2×1 substrate. In spite of the simplicity of the approach, salient features of these systems are properly described. In addition, we find that surface roughening and destruction of the substrate 2×1 dimerization during low-temperature Si deposition is a result of strong Si–Si interaction. Chaotic Al adatoms do not break the surface Si dimers. This is a qualitative difference which can be easily verified experimentally.

Local-density approximation calculations have been used to study the electronic structure of the Al14/n-fold-SiO2 ring/Si15 cluster system for n = 3, 4, 6. The 6-fold ring placed between aluminum and silicon has an insulator character with the fundamental bandgap of 4 eV and the energetic barrier of 3.5 eV. The 4-fold ring has a bandgap of 2 eV, however, its insulator properties are doubtful because of the very small distance between the Fermi level and the first unoccupied state (0.2 eV). The 3-fold-SiO2 ring has not a fundamental gap at all. Considering the Al14/n-fold-SiO2 ring/Si15H18 system as a model of the MOS device, we can predict that the thin silica film ( d ~ 7 A ) can be used as an insulator layer. However, if the thickness is less than 5 A the insulator properties of silica disappear.

We have performed a first-principles local-density cluster investigation of nanoscalep-Si/n-Si junctions. Al and P atoms were used as dopants and Al-P distances were of order a few Angstroms. The thermoemission current-voltage characteristics were calculated in addition to the electronic structure. It was shown that a rectifying nanoscalep-njunction can be formed in silicon if the distance between donor and acceptor atoms is not too small (about 1 nm).

Using the ab initio local density approach we have studied the electronic structure of the systems consisting of the six-, four- and three-fold planar SiO 2 rings placed upon the surface of the silicon cluster. The interaction of the six- and four-fold rings with the silicon surface changes the electronic structure of the silica particle very weakly and the surface insulator band gap of 7–8 eV remains in their densities of states. The electronic structure of the three-fold planar ring undergoes a significant reconstruction. Its surface band gap is 3.7 eV instead of 7.6 eV for the free particle case. Two groups of the interfacial states were found inside the silicon semiconductor band gap.

The nonempirical discrete-variational method of local density approximation was used to study the electronic structure and the most stable position of a single Au atom for the Si(111)–Au chemisorption system. Only the symmetric adsorption sites (H3, T4, "on-top") were considered. The three fold hollow site has been found to be energetically the most favorable position with the vertical distance between adsorbed Au atom and the topmost silicon atom plane of 1.59 Å, binding energy of 4.76 eV and vertical vibrational mode of 87 cm –1. The photoemission spectra were calculated and compared with the experimental spectra. Although the calculations suggest that Au atom can not penetrate under the silicon surface, the possibility has been shown for Au atom to replace the surface silicon atom upon the adsorption. The results of the calculations are discussed in connection with the existing models for initial stages of the Au growth on the Si(111) surface.

The Austin Model 1 semi-empirical method combined with geometry optimization procedure was used to study atomic and electronic structures of nanoscale silica particles containing up to 192 atoms (64 Si and 128 O). Twofold Si–O rings were found to dominate in nanometer sized particles. The fraction of larger rings increases with increasing particle sizes. Bond length and bond angle distributions were calculated. The shortest Si–O, O–O and Si–Si interatomic distances are approximately 1.7, 3.0 and 3.3 A, respectively. Average O–Si–O and Si–O–Si bond angles are approximately 110∘ and 130∘. Average electronic energy band gap is 6.9 eV.