arXiv subjects

A. Bondar

Publications and source records attributed to A. Bondar.

At least 937 records · Page 52Linked to original sources

arXiv2008

Thick GEM versus thin GEM in two-phase argon avalanche detectors

The performance of thick GEMs (THGEMs) was compared to that of thin GEMs in two-phase Ar avalanche detectors, in view of their potential application in coherent neutrino-nucleus scattering, dark-matter search and in other rare-event experiments. The detectors comprised a 1 cm thick liquid-Ar layer followed by either a double-THGEM or a triple-GEM multiplier, operated in the saturated vapor above the liquid phase. Three types of THGEMs were studied: those made of G10 and Kevlar and that with resistive electrodes (RETHGEM). Only the G10-made THGEM showed a stable performance in two-phase Ar with gains reaching 3000. Successful operation of two-phase Ar avalanche detectors with either thin- or thick-GEM multipliers was demonstrated at low detection thresholds, of 4 and 20 primary electrons respectively. Compared to the triple-GEM the double-THGEM multiplier yielded slower anode signals; this allowed applying a pulse-shape analysis to effectively reject noise signals. Noise rates of both multipliers were evaluated in two-phase Ar; with detection thresholds of 20 electrons and applying pulse-shape analysis noise levels as low as 0.007 Hz per 1 cm2 of active area were reached.

physics.ins-det↗

arXiv2008

The WASA Detector Facility at CELSIUS

The WASA 4pi multidetector system, aimed at investigating light meson production in light ion collisions and eta meson rare decays at the CELSIUS storage ring in Uppsala is presented. A detailed description of the design, together with the anticipated and achieved performance parameters are given.

nucl-ex↗

arXiv2008

Measurement of eta meson decays into lepton-antilepton pairs

A search for rare lepton decays of the eta meson was performed using the WASA detector at CELSIUS. Two candidates for double Dalitz decay eta->e+e-e+e- events are reported with a background of 1.3+/-0.2 events. This allows to set an upper limit to the branching ratio of 9.7E-5 (90% CL). The branching ratio for the decay eta->e+e-gamma is determined to (7.8+/-0.5 stat+/-0.8 syst)E-3. An upper limit (90% CL) for the branching ratio for the eta->e+e- decay is 2.7E-5 and a limit for the sum of the eta->mu+mu-mu+mu- and eta->pi+pi-mu+mu- decays is 3.6E-4.

hep-ex↗

arXiv2007

Study of a model-independent method for the measurement of the angle phi_3

This report shows the latest results on the study of the method to determine the angle phi_3 of the unitarity triangle using Dalitz plot analysis of $D^0$ decay from B->DK process in a model-independent way. We concentrate on the case with a limited charm data sample, which will be available from the CLEO-c collaboration in the nearest future, with the main goal to find the optimal strategy for phi_3 extraction. We find that the analysis using decays of D_CP only cannot provide a completely model-independent measurement in the case of limited data sample. The procedure involving binned analysis of B->DK and psi(3770)->(K^0_S pi^+ pi^-)_D(K^0_S pi^+ pi^-)_D decays is proposed, that allows to obtain the phi_3 precision comparable to unbinned model-dependent fit.

hep-ph↗

arXiv2007

First results of the two-phase argon avalanche detector performance with CsI photocathode

The performance of a two-phase Ar avalanche detector with CsI photocathode was studied, with regard to potential application in coherent neutrino-nucleus scattering and dark matter search experiments. The detector comprised a 1 cm thick liquid Ar layer and a triple-GEM multiplier operated in the saturated vapor above the liquid phase; the CsI photocathode was deposited on the first GEM. Successful detection of both primary scintillation and ionization signals, produced by beta-particles in liquid Ar, has for the first time been demonstrated in the two-phase avalanche mode.

physics.ins-det↗

arXiv2006

A two-phase argon avalanche detector operated in a single electron counting mode

The performance of a two-phase Ar avalanche detector in a single electron counting mode was studied, with regard to potential application in coherent neutrino-nucleus scattering and dark matter search experiments. The detector comprised of a 1 cm thick liquid Ar layer and a triple-GEM multiplier operated in the saturated vapour above the liquid phase. Successful operation of the detector in single electron counting mode, in the gain range from 6000 to 40000, has for the first time been demonstrated.

physics.ins-det↗

arXiv2006

Triple-GEM performance in He-based mixtures

The performance of triple-GEM detectors in He+N2 gas mixtures is studied in the range of 1-10 atm. The results obtained are relevant in the field of minimization of ionic space-charge effect in the TPC and neutron detection.

physics.ins-det↗

arXiv2006

Electric and Photoelectric Gates for ion backflow suppression in multi-GEM structures

A new approach to suppress ion backflow in multi-GEM structures is suggested. In this approach, the potential difference applied across the gap between two adjacent GEMs is reversed compared to the standard configuration. In such a gap structure, called Electric Gate, a signal transfer from the first to second GEM is presumably provided by the small residual field still existing at small gate voltages and connecting the holes of the two GEMs. On the other hand, ion backflow between the GEMs turned out to be substantially reduced. We also consider another configuration, called Photoelectric Gate, in which in addition to the Electric Gate configuration, a CsI photocathode is deposited on the second GEM. In the Photoelectric Gate, ion backflow through the gap is fully suppressed and the signal transfer through the gap is provided by the photoelectric mechanism due to either avalanche scintillations in the first GEM or proportional scintillations in the electroluminescence gap replacing the first GEM. The idea of the Electric Gate might find applications in the field of TPC detectors and gas photomultipliers. The idea of the Photoelectric Gate is more relevant in the field of two-phase avalanche detectors.

physics.ins-det↗

arXiv2006

Feasibility study of model-independent approach to phi_3 measurement using Dalitz plot analysis

We present results of a feasibility study of a model-independent way to measure the angle phi_3 of the unitarity triangle. The method involves B->DK decays where the neutral D decays to the K_S Pi+ Pi- final state, together with the sample of decays of CP-tagged D mesons (produced, e. g. in psi(3770)->DDbar process) to the same final state. We consider different approaches to the extraction of phi_3 and obtain the expected statistical accuracy of the phi_3 measurement as a function of B and D_CP statistics.

hep-ph↗

arXiv2005

Light multi-GEM detector for high-resolution tracking systems

Controlled etching of copper electrodes in Gas Electron Multiplier foils allows a reduction of the material budget by more than a factor of two for a triple-GEM detector. Detectors making use of thinned foils provide performances similar to those obtained with standard devices: a gain above 10^4 for a double-GEM, with energy resolution of 27 % fwhm for 5.9 keV X-rays.

physics.ins-det↗

arXiv2005

Two-phase argon and xenon avalanche detectors based on Gas Electron Multipliers

We study the performance of two-phase avalanche detectors based on Gas Electron Multipliers (GEMs) and operated in an electron-avalanching mode in Ar and Xe. Emission, gain, energy resolution and stability characteristics of the detectors were studied. Rather high gains, reaching 5000, and stable operation for several hours were observed in the two-phase Ar avalanche detector using a triple-GEM multiplier. The signals induced by X-rays, beta-particles and gamma-rays were successfully recorded. Preliminary results were obtained in the two-phase Xe avalanche detector: the maximum gain of the triple-GEM in two-phase Xe and Xe+2%CH4 was about 200. The results obtained are relevant in the field of two-phase detectors for dark matter searches, coherent neutrino scattering, PET and digital radiography.

physics.ins-det↗

arXiv2005

GEM operation in helium and neon at low temperatures

We study the performance of Gas Electron Multipliers (GEMs) in gaseous He, Ne and Ne+H2 at temperatures in the range of 2.6-293 K. In He, at temperatures between 62 and 293 K, the triple-GEM structures often operate at rather high gains, exceeding 1000. There is an indication that this high gain is achieved by Penning effect in the gas impurities released by outgassing. At lower temperatures the gain-voltage characteristics are significantly modified probably due to the freeze-out of impurities. In particular, the double-GEM and single-GEM structures can operate down to 2.6 K at gains reaching only several tens at a gas density of about 0.5 g/l; at higher densities the maximum gain drops further. In Ne, the maximum gain also drops at cryogenic temperatures. The gain drop in Ne at low temperatures can be reestablished in Penning mixtures of Ne+H2: very high gains, exceeding 10000, have been obtained in these mixtures at 50-60 K, at a density of 9.2 g/l corresponding to that of saturated Ne vapor near 27 K. The results obtained are relevant in the fields of two-phase He and Ne detectors for solar neutrino detection and electron avalanching at low temperatures.

physics.ins-det↗

arXiv2004

Dalitz Analysis of B->K+pi+pi- and B->K+K+pi-

We report results of the Dalitz analysis of the three-body charmless B->K+pi+pi- and B->K+K+K- decays based on a 140fb^{-1} data sample collected with the Belle detector. Measurements of branching fractions for quasi-two-body decays to scalar-pseudoscalar states: B-> f_0(980)K^+, B-> K^*_0(1430)^0 pi+, and to vector-pseudoscalar states: B-> K^*(892)^0 pi+, B-> rho^0 K+, B-> phi K+ are presented. Upper limits on decays to some pseudoscalar-tensor final states are reported. We also report the new measurement of the B-> chi_c K+ branching fraction in two chi_c decay channels: chi_c-> pi+ pi- and chi_c-> K+K-.

hep-ex↗

arXiv2004

Physics at Super B Factory

This report presents the results of studies that investigate the physics reach at a Super B factory, an asymmetric-energy e^+e^- collider with a design luminosity of 5 x 10^35 cm^-2s^-1, which is around 40 times as large as the peak luminosity achieved by the KEKB collider. The studies focus on flavor physics and CP violation measurements that could be carried out in the LHC era. The physics motivation, key observables, measurement methods and expected precisions are presented. The sensitivity studies are a part of the activities associated with the preparation of a Letter of Intent for SuperKEKB, which has been submitted recently.

hep-ex↗

arXiv2004

Cryogenic avalanche detectors based on gas electron multipliers

We study the performances of gaseous and two-phase (liquid-gas) cryogenic detectors of ionizing radiation based on gas electron multipliers (GEMs) and operated in an avalanche mode in pure noble gases. The gas amplification in He, Ar and Kr is systematically studied at low temperatures, using triple-GEM multipliers. High gains, exceeding 10^4, were obtained in these gases in the range of 120-300 K. Stable electron avalanching was demonstrated in a saturated Kr vapor in the two-phase mode. These results are relevant for understanding basic mechanisms of electron avalanching at low temperatures and for applications in cryogenic particle detectors, in particular in dark matter and solar neutrino detectors.

physics.ins-det↗

arXiv2003

First results from cryogenic avalanche detectors based on gas electron multipliers

We study the performance of gaseous and two-phase (liquid-gas) cryogenic detectors of ionizing radiation, based on gas electron multipliers (GEMs). For the first time, high gas gains, exceeding 10^4, were obtained in pure He, Ar and Kr at low temperatures and the stable avalanche mode of operation was observed in the two-phase cryogenic detector in Kr. The electron avalanching at low temperatures, in the range of 120-300 K, is systematically studied.

physics.ins-det↗

arXiv2002

Further studies of GEM performance in dense noble gases

We further study the performance of single, double and triple Gas Electron Multiplier (GEM) detectors in pure noble gases at high pressures, in the range of 1-10 atm. We confirm that light noble gases, in particular He and its mixtures with Kr, have the highest gain, reaching 10^6, and an unusual gain dependence on pressure. Effects of the number of GEMs, GEM hole diameter and pitch are investigated in detail. In He, avalanche-induced secondary scintillations are observed at high gains, using the metal photocathode. These results are relevant in the field of avalanche mechanism in noble gases and X-ray, neutron and cryogenic particle detectors.

physics.ins-det↗

arXiv2002

Triple GEM operation in compressed He and Kr

We study the performance of the triple GEM (Gas Electron Multiplier) detector in pure noble gases He and Kr at high pressures, varying from 1 to 15 atm. The operation in these gases is compared to that recently studied in Ne, Ar and Xe. It turned out that light noble gases, He and Ne, have superior performance: the highest gain, approaching 10^5, and an unusual gain dependence on pressure. In particular, the maximum gain in He and Ne does not decrease with pressure, in contrast to Ar, Kr and Xe. These results are of high relevance for understanding basic mechanisms of electron avalanching in noble gases and for applications in cryogenic particle detectors, X-ray imaging and neutron detectors.

physics.ins-det↗