90 research outputs found
Wannier and Bloch orbital computation of the nonlinear susceptibility
No full textWe present a method to compute high-order derivatives of the total energy of a periodic solid with respect to a uniform electric field. We apply the 2n + 1 theorem to a recently introduced total energy functional which uses a Wannier representation for the electronic orbitals and we find an expression for the static nonlinear susceptibility which is much simpler than the one obtained by standard perturbative expansions. We show that the zero-field expression of the nonlinear susceptibility can be rewritten in a Bloch representation. We test numerically the validity of our approach with a 1D model Hamiltonian
Density-functional theory of the nonlinear optical susceptibility: Application to cubic semiconductors
No full textWe present a general scheme for the computation of the time-dependent (TD) quadratic susceptibility (chi((2))) of an extended insulator obtained by applying the ''2n + 1'' theorem to the action functional as defined in TD density-functional theory. The resulting expression for chi((2)) includes self-consistent local-field effects, and is a simple function of the linear response of the system. We compute the static chi((2)) of nine III-V and five II-VI semiconductors using the local density approximation (LDA), obtaining good agreement with experiment. For GaP we also evaluate the TD chi((2)) for second-harmonic generation using TD-LDA
Extensive tests of Hybryd Photon Detectors (HPD) used to collect Cherenkov light
No full textThe principle of operation of a newly developed proximity focused Hybrid Photon Detector is described. The HPD characteristics, performance and calibration are reported. Results from beam tests of aerogel threshold counters read out by HPD and the particle identification performance are presented
A DELAY-LINE ON A VLSI GATE ARRAY AS A TIME DIGITIZER
No full textA delay line was developed on a VLSI gate array for drift time measurements on muon chambers of the ZEUS detector at HERA. It consists of 80 cells featuring a 3 ns/cell propagation time; at the start a short pulse is injected into the line and at the stop the status of the line is latched into a 10 byte register. An r.m.s. resolution better than 1 ns was obtained with this reasonably low-cost TDC
The LST analog read-out system of the ZEUS muon detector
No full textA muon position detector based on limited streamer tubes has been built for the ZEUS experiment at the HERA e-p collider at Desy. The tubes are arranged in chambers equipped with electronics circuitry providing an analog read-out of induced signals on strips set orthogonal to the tube wires. The electronic module for charge amplification and conversion will be described including some results obtained from the complete system
Recent results on prototype aerogel threshold counters for particle identification in the region 0.5-4.3 GeV/c
No full textThe recent development of new processes has led to the fabrication of small density silica aerogel with high optical quality. The BaBar experiment, in order to achieve its physics program, requires a good pion/kaon identification capability up to 4.3 GeV/c able to work inside a 1.5 T magnetic field. An aerogel threshold counter using the combination of two refractive indices (1.055 and 1.007) can be used to complete the angular coverage of the particle identification system in the forward region. Different detector geometries read out by two photodetector types (fine mesh phototubes and hybryd photodiodes) have been considered and tested in a CERN beam test
THE ZEUS BARREL AND REAR MUON DETECTOR
No full textDesign, construction and performance characteristics of the ZEUS barrel and rear muon detector are presented
The SuperB muon detector, status and perspectives2012 IEEE Nuclear Science Symposium and Medical Imaging Conference Record (NSS/MIC)
No full textThe superB project foresees the construction of a high intensity super-flavor factory at the Cabibbo Lab, in Tor Vergata (near Rome). The experiment, based on a high intensity asymmetric electron-positron collider, and on the related detector, is expected to reach a very high luminosity: 2 × 10^36cm-2s-1, that will allow the high statistic study of rare decays and, possibly, will show evidences of new physics
Measurement of the proton structure function F-2 at low x and low Q(2) at HERA
No full textWe report on a measurement of the proton structure function F 2 in the range 3.5×10-5≤x≤4×10-3 and 1.5 GeV2≤Q 2≤15GeV2 at the ep collider HERA operating at a centre-of-mass energy of √s=300GeV. The rise of F 2 with decreasing x observed in the previous HERA measurements persists in this lower x and Q 2 range. The Q 2 evolution of F 2, even at the lowest Q 2 and x measured, is consistent with perturbative QCD. © 1996 Springer-Verlag
The Instrumented Flux Return Detector of the SuperB Experiment: R&D Studies and First Results of the Fermilab Beam Test
No full textAbstractSuperB is a super-flavor factory that will be built in Tor Vergata (Italy). The project, recently approved by the Italian Government, and classified as the flagship project of the Italian INFN, foresees the construction of a high intensity asymmetric electron-positron collider and of the related detector. The expected luminosity of 2x1036cm−2 s−1, a factor 100 higher than the last generation of B-factories, will allow the high statistic study of rare decays and, possibly, will allow a deeper insight in the field of new physics. Part of the SuperB apparatus is the Instrumented Flux Return (IFR). This detector exploits the flux return iron structure of the superconducting solenoid as absorber for the identification of muons and neutral hadrons. In more details, It consists of ≃ 92 cm of iron interleaved by 9 layers of highly segmented scintillators. The detection technique is based on relatively inexpensive extruded plastic scintillator bars produced at the FNAL-NICADD facility. The scintillation light is collected through Wave Length Shifting fibers and guided to recently developed devices called Silicon Photon Multipliers used as photodetectors. The use of plastic scintillator as active material ensures reliability, robustness and long term stability while the high granularity and the fast response guarantee a good space-time resolution, extremely important to cope with the expected high particles flux. The readout scheme under evaluation is this manuscript is the double coordinate readout (“BIRO readout”) where two layers of orthogonal scintillator bars provide both, the polar and azimuthal coordinate. In order to deeply understand the performances and possible drawbacks of the above technique, a full depth prototype has been designed and built in Ferrara and Padova, and tested at the Fermilab Test Beam Facility (FBTF) in December 2010. In this paper a comprehensive description of the IFR related R&D studies will be presented. In particular, we will focus on the results of the Fermilab beam test, issues and future activities will also be outlined
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