On the low-temperature performances of THGEM and THGEM/G-APD multipliers in gaseous and two-phase Xe

The performances of THGEM multipliers in two-phase Xe avalanche mode are presented for the first time. Additional results on THGEM operation in gaseous Xe at cryogenic temperatures are provided. Stable operation of a double-THGEM multiplier was demonstrated in two-phase Xe with gains reaching 600. These are compared to existing data, summarized here for two-phase Ar, Kr and Xe avalanche detectors incorporating GEM and THGEM multipliers. The optical readout of THGEMs with Geiger-mode Avalanche Photodiodes (G-APDs) has been investigated in gaseous Xe at cryogenic temperature; avalanche scintillations were recorded in the Near Infrared (NIR) at wavelengths of up to 950 nm. At avalanche charge gain of 350, the double-THGEM/G-APD multiplier yielded 0.07 photoelectrons per initial ionization electron, corresponding to an avalanche scintillation yield of 0.7 NIR photons per avalanche electron over 4pi. The results are compared with those of two-phase Ar avalanche detectors. The advantages, limitations and possible applications are discussed.Comment: 22 pages, 14 figures. Revised Figs. 10,11 and Table 1. To be published in JINS

Electroproduction, photoproduction, and inverse electroproduction of pions in the first resonance region

Methods are set forth for determining the hadron electromagnetic structure in the sub-$N\bar{N}$-threshold timelike region of the virtual-photon ``mass'' and for investigating the nucleon weak structure in the spacelike region from experimental data on the process $\pi N\to e^+e^- N$ at low energies. These methods are formulated using the unified description of photoproduction, electroproduction, and inverse electroproduction of pions in the first resonance region in the framework of the dispersion-relation model and on the basis of the model-independent properties of inverse electroproduction. Applications of these methods are also shown.Comment: The revised published version; Revtex4, 18 pages, 6 figure

Sound and Heat Absorption by a 2D Electron Gas in an Odd-Integer Quantized-Hall Regime

The absorption of bulk acoustic phonons in a two-dimensional (2D) GaAs/AlGaAs heterostructure is studied (in the clean limit) where the 2D electron-gas (2DEG), being in an odd-integer quantum-Hall state, is in fact a spin dielectric. Of the two channels of phonon absorption associated with excitation of spin waves, one, which is due to the spin-orbit (SO) coupling of electrons, involves a change of the spin state of the system and the other does not. We show that the phonon-absorption rate corresponding to the former channel (in the paper designated as the second absorption channel) is finite at zero temperature ($T$), whereas that corresponding to the latter (designated as the first channel) vanishes for $T\to 0$. The long-wavelength limit, being the special case of the first absorption channel, corresponds to sound (bulk and surface) attenuation by the 2DEG. At the same time, the ballistic phonon propagation and heat absorption are determined by both channels. The 2DEG overheat and the attendant spin-state change are found under the conditions of permanent nonequilibrium phonon pumping.Comment: 26 pages, 2 figure