The NEXT neutrinoless double beta decay (betabeta0nu) experiment will use a high-pressure gas electroluminescence-based TPC to search for the decay of Xe-136. One of the main advantages of this ...technology is the possibility to reconstruct the topology of events with energies close to Q sub(betabeta). The rejection potential associated to the topology reconstruction is limited by our capacity to properly reconstruct the original path of the electrons in the gas. This reconstruction is limited by different factors that include the geometry of the detector, the density of the sensors in the tracking plane and the separation among them, etc. Ultimately, the resolution is limited by the physics of electron diffusion in the gas. In this paper we present a series of molecular additives that can be used in Xenon gas at very low partial pressure to reduce both longitudinal and transverse diffusion. We will show the results of different Monte-Carlo simulations of electron transport in the gas mixtures from wich we have extracted the value of some important parameters like diffusion, drift velocity and light yields. These results show that there is a series of candidates that can reduce diffusion without affecting the energy resolution of the detector and they should be studied experimentally. A comparison with preliminary results from such an ongoing experimental effort is given.
We present the results of the first in-beam studies of a medium size (10 x 10 cm super(2)) Resistive-Plate WELL (RPWELL): a single-sided THGEM coupled to a pad anode through a resistive layer of high ...bulk resistivity (~10 super(9)Omegacm). The 6.2 mm thick (excluding readout electronics) single-stage detector was studied with 150 GeV muons and pions. Signals were recorded from 1x1 cm super(2) square copper pads with APV25-SRS readout electronics. The single-element detector was operated in Ne/(5%CH sub(4)) at a gas gain of a few times 10 super(4), reaching 99% detection efficiency at average pad multiplicity of ~1.2. Operation at particle fluxes up to ~10 super(4) Hz/cm super(2) resulted in ~23% gain drop leading to ~5% efficiency loss. The striking feature was the discharge-free operation, also in intense pion beams. These results pave the way towards robust, efficient large-scale detectors for applications requiring economic solutions at moderate spatial and energy resolutions.
In-beam evaluation of a fully-equipped medium-size 30 x 30 cm super(2) Resistive Plate WELL (RPWELL) detector is presented. It consists here of a single element gas-avalanche multiplier with Semitron ...ESD225 resistive plate, 1 cm super(2) readout pads and APV25/SRS electronics. Similarly to previous results with small detector prototypes, stable operation at high detection efficiency (> 98%) and low average pad multiplicity (~ 1.2) were recorded with 150 GeV muon and high-rate pion beams, in Ne/(5%CH sub(4)), Ar/(5%CH sub(4)) and Ar/(7%CO sub(2)). This is an important step towards the realization of robust detectors suitable for applications requiring large-area coverage; among them Digital Hadron Calorimetry.
Discrepancies between the measured and simulated gain in Thick-Micropatterned gaseous detectors (MPGD), namely THGEM, have been observed by several groups. In order to simulate the electron ...avalanches and the gain the community relies on the calculations performed in Garfield++, known to produce differences of 2 orders of magnitude in comparison to the experimental data for thick MPGDs. In this work, simulations performed for Ne/5%CH sub(4), Ar/5%CH sub(4) and Ar/30%CO sub(2) mixtures shows that Garfield++ is able to perfectly describe the experimental data if Penning effect is included in the simulation. The comparison between the number of excitations which may lead to a Penning transfer, is shown for THGEM and GEM, explaining the less pronounced gain discrepancies observed in GEM.
The simulation of Micro Pattern Gaseous Detectors (MPGDs) signal response is an important and powerful tool for the design and optimization of such detectors. However, several attempts to exactly ...simulate the effective gas gain have not been completely successful. Namely, the gain stability over time has not been fully understood. Charging-up of the insulator surfaces have been pointed as one of the responsible for the difference between experimental and Monte Carlo results. This work describes two iterative methods to simulate the charging-up in one MPGD device, the Gas Electron Multiplier (GEM). The first method, which uses a constant step size for avalanches time evolution, is very detailed but slow to compute. The second method instead uses a dynamic step-size that improves the computing time. Good agreement between both methods was achieved. Comparison with experimental results shows that charging-up plays an important role in detectors operation, explaining the time evolution of the gain. However it doesn't seem to be the only responsible for the difference between measurements and Monte Carlo simulations.
We present a novel concept for the suppression of secondary ions in gaseous detectors. The Zero Ion Backflow electron multiplier operates in a noble gas atmosphere and effectively suppresses the ion ...back flow to the level of primary ionization, totally blocking the secondary ions produced in the multiplier. This detector is composed by a proportional scintillation region, established between two highly transparent meshes, followed by a Gaseous Photomultiplier (GPM). The ionization electrons drift towards the scintillation region, where a proportional electroluminescence signal is produced, without the production of any secondary ionization. A fraction of the emitted VUV scintillation is collected by the photocathode of the GPM and the photoelectron signal is amplified in the GPM through electron avalanche processes. The positive ions of the avalanches developed in the GPM are totally blocked by the mesh that separates the scintillation region and the GPM, resulting in full ion back-flow suppression of secondary ions into the drift/conversion region of the detector. The full suppression capability is independent of the GPM gain. The Zero Ion Backflow electron multiplier is an alternative to readout the ionization signals of Time Projection Chambers in which the accumulation of secondary ions in the sensitive region of the detector has the potential to affect its performance.
In this work, a new position sensitive gas photomultiplier (GPM) based on a cascade configuration is proposed. The GPM is composed by two THGEMs, followed by a 2D-THCOBRA being operated in ...Ne/CH4(5%), at a pressure of 1 bar in VUV single photon mode. The 2D-THCOBRA is a hybrid microstructure which combines the benefits of a THGEM and a 2D-MHSP, presenting two independent charge multiplication stages. The position capability is performed by using two orthogonal resistive lines crossing each one the readout electrodes. The position is obtained by measuring the charge sharing in both ends of each resistive line, by using only 2 readout channels. This work focuses the study of the detector gain, Ion Back Flow (IBF) and spatial resolution. A charge gain of 10 super(6) and an Ion Back Flow (IBF) values of about 20% were measured. Position resolutions below 300 mu m (FWHM) were obtained for single VUV photon counting mode operation.
We plan to measure several 2S -2P transition frequencies in ... and ... by means of laser spectroscopy with an accuracy of 50 ppm. This will lead to a determination of the corresponding nuclear rms ...charge radii with a relative accuracy of 3 x 10..., limited by the uncertainty of the nuclear polarization contribution. First, these measurements will help to solve the proton radius puzzle. Second, these very precise nuclear radii are benchmarks for ab initio few-nucleon theories and potentials. Finally when combined with an ongoing measurement of the 1S - 2S transition in He+, these measurements will lead to an enhanced bound-state QED test of the 1S Lamb shift in He+. (ProQuest: ... denotes formulae/symbols omitted.)
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Accurate knowledge of the charge and Zemach radii of the proton is essential, not only for understanding its structure but also as input for tests of bound-state quantum electrodynamics and its ...predictions for the energy levels of hydrogen. These radii may be extracted from the laser spectroscopy of muonic hydrogen (μp, that is, a proton orbited by a muon). We measured the $2{\mathrm{S}}_{1/2}^{\mathrm{F}=0}-2{\mathrm{P}}_{3/2}^{\mathrm{F}=1}$ transition frequency in μp to be 54611.16(1.05) gigahertz (numbers in parentheses indicate one standard deviation of uncertainty) and reevaluated the $2{\mathrm{S}}_{1/2}^{\mathrm{F}=1}-2{\mathrm{P}}_{3/2}^{\mathrm{F}=1}$ transition frequency, yielding 49881.35(65) gigahertz. From the measurements, we determined the Zemach radius, r Z = 1.082(37) femtometers, and the magnetic radius, r M = 0.87(6) femtometer, of the proton. We also extracted the charge radius, r E = 0.84087(39) femtometer, with an order of magnitude more precision than the 2010-CODATA value and at 7σ variance with respect to it, thus reinforcing the proton radius puzzle.
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