237 research outputs found
3D Simulation of Electron and Ion Transmission of GEM-based Detectors
Time Projection Chamber (TPC) has been chosen as the main tracking system in
several high-flux and high repetition rate experiments. These include on-going
experiments such as ALICE and future experiments such as PANDA at FAIR and ILC.
Different activities were carried out on the adoption
of Gas Electron Multiplier (GEM) as the gas amplification stage of the
ALICE-TPC upgrade version. The requirement of low ion feedback has been
established through these activities. Low ion feedback minimizes distortions
due to space charge and maintains the necessary values of detector gain and
energy resolution. In the present work, Garfield simulation framework has been
used to study the related physical processes occurring within single, triple
and quadruple GEM detectors. Ion backflow and electron transmission of
quadruple GEMs, made up of foils with different hole pitch under different
electromagnetic field configurations (the projected solutions for the ALICE
TPC) have been studied. Finally a new triple GEM detector configuration with
low ion backflow fraction and good electron transmission properties has been
proposed as a simpler GEM-based alternative suitable for TPCs for future
collider experiments
Development of neutron and X-ray imaging detectors based on MHSP
Doutoramento em FísicaA Micro-Hole & Strip Plate (MHSP) é uma microestrutura desenvolvida recentemente em instituições universitárias portuguesas. Neste trabalho, o seu desempenho como detector para imagiologia é explorado, tendo como objectivo a imagiologia não só de neutrões, mas também de raios X. A aplicação do método da divisão resistiva de carga é aplicada a uma MHSP especialmente desenhada para sensibilidade em posição. Várias abordagens em termos da electrónica de aquisição de sinal são testadas, sem perder de vista a relação desempenho-preço. Resoluções espaciais abaixo de 1 mm foram obtidas com a MHSP a operar em xénon e tetrafluorometano, com um sistema de detecção a um preço modesto quando comparado com as alternativas, e apropriado para inúmeras aplicações em imagiologia de neutrões e de raios X.The Micro-Hole & Strip Plate (MHSP) is a Micropattern Gaseous Detector developed recently in Portuguese institutions. In this work, its performance as a imaging detector is characterised, aiming neutron imaging, but also with results in X-ray imaging. The application of the method of resistive charge division is used in a MHSP specially designed for position sensitivity. Several different electronic approaches for signal collection are tested, always taking into account the performance-price ratio. Position resolutions below 1 mm were achieved with the MHSP operating in xenon and in tetrafluoromethane, in a very cost effective detector setup, suitable for many applications in neutron and X-ray imaging
Beam Studies of the Segmented Resistive WELL: a Potential Thin Sampling Element for Digital Hadron Calorimetry
Thick Gas Electron Multipliers (THGEMs) have the potential of constituting
thin, robust sampling elements in Digital Hadron Calorimetry (DHCAL) in future
colliders. We report on recent beam studies of new single- and
double-THGEM-like structures; the multiplier is a Segmented Resistive WELL
(SRWELL) - a single-faced THGEM in contact with a segmented resistive layer
inductively coupled to readout pads. Several 1010 cm configurations
with a total thickness of 5-6 mm (excluding electronics) with 1 cm pads
coupled to APV-SRS readout were investigated with muons and pions. Detection
efficiencies in the 98 range were recorded with average pad-multiplicity of
1.1. The resistive anode resulted in efficient discharge damping, with
potential drops of a few volts; discharge probabilities were for
muons and for pions in the double-stage configuration, at rates
of a few kHz/cm. Further optimization work and research on larger detectors
are underway.Comment: Presented at the Vienna Conference on Instrumentation,
February 2013 and submitted to its proceeding
Shedding light on X17: community report
The workshop “Shedding light on X17” brings together scientists looking for the existence of a possible new light particle, often referred to as X17. This hypothetical particle can explain the resonant structure observed at ∼ 17 MeV in the invariant mass of electron-positron pairs, produced after excitation of nuclei such as 8Be and 4He by means of proton beams at the Atomki Laboratory in Debrecen. The purpose of the workshop is to discuss implications of this anomaly, in particular theoretical interpretations as well as present and future experiments aiming at confirming the result and/or at providing experimental evidence for its interpretation
Azimuthal anisotropy of charged jet production in root s(NN)=2.76 TeV Pb-Pb collisions
We present measurements of the azimuthal dependence of charged jet production in central and semi-central root s(NN) = 2.76 TeV Pb-Pb collisions with respect to the second harmonic event plane, quantified as nu(ch)(2) (jet). Jet finding is performed employing the anti-k(T) algorithm with a resolution parameter R = 0.2 using charged tracks from the ALICE tracking system. The contribution of the azimuthal anisotropy of the underlying event is taken into account event-by-event. The remaining (statistical) region-to-region fluctuations are removed on an ensemble basis by unfolding the jet spectra for different event plane orientations independently. Significant non-zero nu(ch)(2) (jet) is observed in semi-central collisions (30-50% centrality) for 20 <p(T)(ch) (jet) <90 GeV/c. The azimuthal dependence of the charged jet production is similar to the dependence observed for jets comprising both charged and neutral fragments, and compatible with measurements of the nu(2) of single charged particles at high p(T). Good agreement between the data and predictions from JEWEL, an event generator simulating parton shower evolution in the presence of a dense QCD medium, is found in semi-central collisions. (C) 2015 CERN for the benefit of the ALICE Collaboration. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).Peer reviewe
Production of He-4 and (4) in Pb-Pb collisions at root(NN)-N-S=2.76 TeV at the LHC
Results on the production of He-4 and (4) nuclei in Pb-Pb collisions at root(NN)-N-S = 2.76 TeV in the rapidity range vertical bar y vertical bar <1, using the ALICE detector, are presented in this paper. The rapidity densities corresponding to 0-10% central events are found to be dN/dy4(He) = (0.8 +/- 0.4 (stat) +/- 0.3 (syst)) x 10(-6) and dN/dy4 = (1.1 +/- 0.4 (stat) +/- 0.2 (syst)) x 10(-6), respectively. This is in agreement with the statistical thermal model expectation assuming the same chemical freeze-out temperature (T-chem = 156 MeV) as for light hadrons. The measured ratio of (4)/He-4 is 1.4 +/- 0.8 (stat) +/- 0.5 (syst). (C) 2018 Published by Elsevier B.V.Peer reviewe
Forward-central two-particle correlations in p-Pb collisions at root s(NN)=5.02 TeV
Two-particle angular correlations between trigger particles in the forward pseudorapidity range (2.5 2GeV/c. (C) 2015 CERN for the benefit of the ALICE Collaboration. Published by Elsevier B. V.Peer reviewe
Event-shape engineering for inclusive spectra and elliptic flow in Pb-Pb collisions at root(NN)-N-S=2.76 TeV
Peer reviewe
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