172 research outputs found

    Status of the R&D activities for the upgrade of the ALICE TPC

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    After the Long Shutdown 2 the LHC will provide lead-lead collisions at interaction rates as high as 50kz. In order to cope with such conditions the ALICE Time Projection Chamber (TPC) needs to be upgraded. After the upgrade the TPC will run in a continuous mode, without any degradation of the momentum and dE/dx resolution compared to the performance of the present TPC. Since readout by multi-wire proportional chambers is no longer feasible with these requirements, new technologies have to be employed. In the new readout chambers the electron amplification is provided by a stack of four Gas Electron Multiplier (GEM) foils. Their high voltage settings and orientation have been optimised to provide an energy resolution better then 12% at the photopeak of 55Fe. At the same settings the Ion BackFlow into the drift volume is less than 1% of the effective number of ions produced during gas amplification and the primary ionisations. This is necessary to prevent the accumulation of space charge, which eventually will distort the field in the drift volume. To ensure stable operation at the high loads during LHC run 3 the chambers have to be robust against discharges, too. With the selected configuration in a quadruple GEM stack the discharge probability is kept at the level of 10−1210^{-12} discharges per incoming hadron. An overview of the ALICE TPC upgrade activities will be given in these proceedings and the optimised settings foreseen for the GEM stacks of the future readout chambers are introduced. Furthermore the outcome of two beam time campaigns at SPS and PS (at CERN) in the end of 2014 is shown. At this campaigns the stability against discharges and the dE/dx performance of a full size readout chamber prototype was tested. In addition it is reported on charging-up studies of 4GEM stacks and on tests of electromagnetic sagging of large GEM foils.Comment: 4 pages, 3 figures, Proceedings of "4th Conference on Micro-Pattern Gaseous Detectors

    Measurements of ion mobility in argon and neon based gas mixtures

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    As gaseous detectors are operated at high rates of primary ionisation, ions created in the detector have a considerable impact on the performance of the detector. The upgraded ALICE Time Projection Chamber (TPC) will operate during LHC Run 3\,3 with a substantial space charge density of positive ions in the drift volume. In order to properly simulate such space charges, knowledge of the ion mobility KK is necessary. To this end, a small gaseous detector was constructed and the ion mobility of various gas mixtures was measured. To validate the corresponding signal analysis, simulations were performed. Results are shown for several argon and neon based mixtures with different CO2\textrm{CO}_2 fractions. A decrease of KK was measured for increasing water content.Comment: 3 pages, 2 figure

    Measurements of ion mobility and GEM discharge studies for the upgrade of the ALICE time projection chamber

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    ALICE is one of the four experiments at the Large Hadron Collider (LHC). The quark-gluon plasma, which is predominantly produced in lead-lead collisions at LHC, is of particular interest for ALICE. After the long shut-down 2 (2019-2021) the LHC will provide lead-lead collisions at an increased interaction rate of 50 kHz. In order to examine every event at this interaction rate the ALICE Time Projection Chamber (TPC) needs to be upgraded. The TPC’s ReadOut Chambers (ROCs) are currently multi-wire proportional chambers. To prevent space charge build-up of slow ions, drifting from the ROCs into the TPC, a gating grid is used. The corresponding closure time imposes a dead time on the TPC read out, which prohibits data taking at a readout rate higher than 3 kHz. New ROCs have therefore been designed, relying on stacks of Gas Electron Multiplier (GEM) foils for the gas amplification, allowing for continuous readout. With the new ROCs, a certain fraction of ions will be drifting at all time into the TPC. Knowing the exact ion mobility in the counting gas is thus required in order to determine which amount of ion-back drift is tolerable. In this work we study the ion mobility in Ne-CO2-N2 (90-10-5), which is the gas mixture for the upgraded TPC, as well in several other argon- and neon-based mixtures. During stability studies for the new ROCs the phenomenon of secondary discharges has been observed. We thus also study discharges in GEM stacks and provide a detailed investigation of secondary discharges

    ARIADNE+: Large scale demonstration of fast optical readout for dual-phase LArTPCs at the CERN Neutrino Platform

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    Optical readout of large scale dual-phase liquid Argon TPCs is an attractive alternative to charge readout and has been successfully demonstrated on a 2x2m active region within the CERN protoDUNE cold box. ARIADNE+ uses four Timepix3 cameras imaging the S2 light produced by 16 novel, patent pending, glass THGEMs. ARIADNE+ takes advantage of the raw Timepix3 data coming natively 3D and zero suppressed with a 1.6ns timing resolution. Three of the four THGEM quadrants implement readout in the visible light range through wavelength shifting, with the fourth featuring a VUV light intensifier, thus removing the need for wavelength shifting altogether. Cosmic ray reconstruction and energy calibration was performed. Presented is a summary of the detector setup and experimental run, preliminary analysis of the run data and future outlook for the ARIADNE program.Comment: Proceedings for NuFACT202

    Dosimetry and calorimetry performance of a scientific CMOS camera for environmental monitoring

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    This paper explores the prospect of CMOS devices to assay lead in drinking water, using calorimetry. Lead occurs together with traces of radioisotopes, e.g.,210 Pb, producing γ-emissions with energies ranging from 10 keV to several 100 keV when they decay; this range is detectable in silicon sensors. In this paper we test a CMOS camera (OXFORD INSTRUMENTS Neo 5.5) for its general performance as a detector of X-rays and low energy γ-rays and assess its sensitivity relative to the World Health Organization upper limit on lead in drinking water. Energies from 6 keV to 60 keV are examined. The CMOS camera has a linear energy response over this range and its energy resolution is for the most part slightly better than 2%. The Neo sCMOS is not sensitive to X-rays with energies below ∼ 10 keV. The smallest detectable rate is 40 ± 3 mHz, corresponding to an incident activity on the chip of 7 ± 4 Bq. The estimation of the incident activity sensitivity from the detected activity relies on geometric acceptance and the measured efficiency vs. energy. We report the efficiency measurement, which is 0.08(2)% (0.0011(2)%) at 26.3 keV (59.5 keV). Taking calorimetric information into account we measure a minimal detectable rate of 4 ± 1 mHz (1.5 ± 0.1 mHz) for 26.3 keV (59.5 keV) γ-rays, which corresponds to an incident activity of 1.0 ± 0.6 Bq (57 ± 33 Bq). Toy Monte Carlo and Geant4 simulations agree with these results. These results show this CMOS sensor is well-suited as a γ-and X-ray detector with sensitivity at the few to 100 ppb level for210 Pb in a sample

    Forward-central two-particle correlations in p-Pb collisions at root s(NN)=5.02 TeV

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    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

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    Production of He-4 and (4) in Pb-Pb collisions at root(NN)-N-S=2.76 TeV at the LHC

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    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
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