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The Ardm -1T Experiment

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The Ardm -1T Experiment 17-18 November 2008 The ArDM -1t Experiment P. Otyugova (University of Zurich), on behalf of ArDM collaboration. ETH Zurich, Switzerland: A. Badertscher, L. Kaufmann, L. Knecht, M. Laffranchi, C.Lazzaro, A. Marchionni, G. Natterer, F. Resnati, A. Rubbia (spokesperson), J. Ulbricht. Zurich University, Switzerland: C. Amsler, V. Boccone, A. Dell’Antone S. Horikawa, P.Otyugova C. Regenfus, J. Rochet. University of Granada, Spain: A. Bueno, M.C. Carmona-Benitez, J. Lozano, A. Melgarejo, S. Navas-Concha. CIEMAT, Spa in: MDM. Dan iliel, M. dPdde Prado, LRL. Romero. Soltan Institute for Nuclear Studies, Poland: P. Mijakowski, P. Przewlocki, E. Rondio. University of Sheffield, England: P.Lightfoot, K.Mavrokoridis, M. Robinson, N. Spooner. Estimated event rates for ArDM ~1 evt/ton/day ~0010.01 evt/ton/day Assumptions for simulation: For 30 keV nuclear • Cross-section normalized to nucleon recoil on Argon →σ= 10–42 cm2 =10–6 pb → MWIMP = 100 GeV • Halo Model → WIMP Density = 0.5 GeV/cm3 → vesc = 600 km/s • Interaction → Spin independent → Engel Form factor P.Ot y u gova ( U n i Z H ) ArDM WIMP Detection Principal Scattered WIMP WIMP Speed of the WIMP: 230 km/s The expected Ar recoil energies: WIMP Ar 10-100 keV. A Ar atom at rAr rest Ar atom undergoes a recoil Scintillation (light) Recoiling Light: AtArgon atom Is seen by the PMTs Charge: Extracted and detected Ionization with a good spatial (charge) resolution by a double stage LEM system. P.Ot y u gova ( U n i Z H ) The ArDM main parameters Detector Max. drift length 120 cm Target mass 850 kg Readout method Independent readout of charge& light Drift field 1÷4 kV/cm Charge readout Charge gain 500÷103 per e- Light readout Global light collection efficiency 1÷2% Background rejection is based on: 1. Light pulse shape discrimination. Different light structure for WIMP-like (nuclear recoil) events and e/γ-like events. 2. Different Light/Charge rations for WIMP and e/γ-like events P.Ot y u gova ( U n i Z H ) General Layout of the Experiment Double stage LEM System A. Rubbia, “ArDM: a Ton-scale liquid Argon experiment for 14 Cryogenic PMTs to detect the scintillation direct detection of dark matter in the universe”, J. Phys. Conf. Ser. 39 (2006) light 129 P.Ot y u gova ( U n i Z H ) Strategy 1. Assemble the detector and test the performance ofllthf all the sys tems an d subde tec tors. 2. Fully characterize response of the detector on surface – Response to gamma, electron and neutron radiations – Partic le ident ificat ion – Calibration of the detector with mono-energetic neutrons, gammas and electrons. 3. The underground (low background) operation of the detector is considered . P.Ot y u gova ( U n i Z H ) The ArDM design and assembly Two-stage LEM. 800mm di ame ter The inner detector PMTs HV system mm 1200m Field shapers 14 PMTs blbelow t he cat hdhode to detect the scintillation light. Input/output Support of the recirculation pillars Cathode system P.Ot y u gova ( U n i Z H ) Assembly at CERN Setpember 2007- May 2008 P.Ot y u gova ( U n i Z H ) ArDM Cryogenics and LAr purification 0 l 00 14 vacuum insulation LN2 cooling jacket 00 l 44 1 non-purified LAr cooling bath pure LAr closed circuit In collaboration with BIERI engineering Recirculation and CuO Winterthur, Switzerland purification cartridge Bellow pump P.Ot y u gova ( U n i Z H ) LAr Pump tests 30 cm3 volume In collaboration with BIERI engineering Winterthur, Switzerland Pump cycle (s) P.Ot y u gova ( U n i Z H ) Measured LAr flux ~ 20 l/hr Slow Control System LAr bath capacitive Levelmeters P.Ot y u gova ( U n i Z H ) First ArDM cooldown temperature sensors along the detector axis ~ 20h refilling of the external bath Precooling of the GAr @ Warming Up extlbthternal bath 04b0.4bar 9:00 16:00 GAr @ 23:00 04:00 6th May 8th May 10thMay 13th May 1. 1bar P.Ot y u gova ( U n i Z H ) HV and the Drift Field The drift field is supplied by Greinacher (Cocroft-Walton) circuit directly connected to the field-shaping rings. Edrift~ 4kV/cm. The 210 stage circuit is fully assembled and successfully tested in liquid Nitrogen. Stable operation in air at 120 kV. ges 210 sta Polypropylene capacitors 4x82 nF, 2.5 kV/stage, 210 stages P.Ot y u gova ( U n i Z H ) Charge Read-Out System: Large Electron Multiplier (LEM) LAr LEM-TPC principal Anode (with strips) The top Electrode of the LEM2 (with strips) LEM2 LEM1 Charge LAr level extraction grids 10 x 10 cm2 ppyprototype chamber Two planes 16 strips, 6 mm width F.Resnati Proceeding for IEEE-NSS 2008 Produced by standard PCB technique Cathode Double-sided copper-clad (18 μm layer) FR4 plates Precision holes made by drilling Gold deposition on Cu (<~ 1 μm layer) to avoid oxidization For the details see talk of A.Marchionni. P.Ot y u gova ( U n i Z H ) LEM-TPC operation in pure GAr at 300K TLEMTop LEM AdAnode Ar gas (Ar-60) at room view view temperature @ 1.2 bar Typical electric field values E(V/cm)E (V/cm) s Anode-LEM2 760 event LEM2 ~14 103 (()*) yy LEM2-LEM1 590 mic ra LEM1 ~14 103 (()*) ss Drift 420 (()*) Electric field is defined as ΔV/d co ical pp Ty Gain ~ 1000 (see next slides) P.Ot y u gova ( U n i Z H ) Source Events in GAr 55Fe and 109Cd sources positioned 2cm below the cathode grid Pure GAr 55Fe and 109Cd LEM electrode spectrum 1.2bar room temp 55Fe (Full Peak) 109Cd ~22.3 keV ~5.9 keV 24.7% FWHM 29.3% FWHM 0.5 kBq 696.9 kBq The device gain (G) depends on the electric field in the LEM holes, on the thickness of the LEM and on the gas density: 55 2 (2αx) Fe (Escape Peak) G=GLEM1GLEM2=G LEM=e ;x≈1mm ~2.9 keV α≈ Ape(-Bp/E)-TdTownsend coeffic ient 42% FWHM A=5.8104 cm-1 bar-1 ± 30% B=9104 Vcm-1 bar-1 ±4% Gains (and α coefficient) consistent with values estimated with MAGBOLTZ P.Ot y u gova ( U n i Z H ) LEM TPC operation in double-phase at 87K LEM Anode LEM electrodes electrodes Proof of operation of double Anode phase LAr LEM Time Projection Chamber as a tracking device. Without continuous LAr purification circuit: Observed electron life time ≈ 10μs Impurities ≈ 30 ppb ox.eq. LAr recirculation circuit is under construction P.Ot y u gova ( U n i Z H ) Light Signal The light signal from the PMT installed in the bottom of the LEM-TPC Proportional scintillation In the drift gap Primary Ionization Scintillation due to electrons the multiplication in the LEM holes Primary scintillation The primary, proportional and LEM-produced lights are visible! P.Ot y u gova ( U n i Z H ) LAr scintillation mechanism 1Σ+ Argon eximer Ar Unbound ground state g 1Σ 3Σ u, u + 128±5 nm photon Ar (not absorbed in atomic Ar) LAr: two characteristic decay times: 5ns, 1.6µs g) oo e/γ-like Nuclear recoil-like litude (l pp Am Time O(µs) 1Σ u-characteristic decay time : O(ns), strongly allowed 3Σ u -characteristic decay time: O(μs), allowed due to the spin-orbit coupling in Ar2, supressed by impurities. Excitation ratio of the two levels depends on the ionization density. VUV li g ht de tec tion: WLS is requ ire d Solution: Tetra-Phenyl-Butadiene (TPB) 128 nm -> 430nm P.Ot y u gova ( U n i Z H ) Development of the Wavelength Shifter. Measurements in GAr Choice of the reflector type 241Am CAmslerC.Amsler et al., “Luminescence quenching of the triplet excimer state by air traces The yield of the triplet-state light component in gaseous argon” arXiv:0708.2621 is significantly purity sensitive! P.Ot y u gova ( U n i Z H ) Optimization of a wavelength shifter , measurements in GAr The setup to define the wavelength shifting Methods of TPB coating: spraying and evaporation The used reflector foils: 3M and TTX 3M: multilayer reflecting polymer film, high radio-purity. TTX (Tetratex): an aligned polytetrafluoroethylene (PTFE) fibrous cloth. TTX coating is preferable to 3M foil. Reason: 1. Better light yield. 2. Better tolerance to the TPB layer thickness. K.Mavrokoridis Proceeding for the IDM 2008 P.Ot y u gova ( U n i Z H ) Test of the PMT window coating (GAr) Test setup for the studies Results for the PMT window coating, evaporation of the PMT coatings. and spray. The best coating method is vacuum evaporation, it produces homogenous deposition of TPB. The PMT window coating with TPB evaporation and with TPB in polystyrene matrix show the best result within the performed measurements. P.Ot y u gova ( U n i Z H ) The Reflectors The inner surface of the field shaping rings is covered reflector foils (Tetratex) coated with wave length shifter (TPB). The TPB coating was evaporated on the A special evaporator was invented and surface of the reflector. constracted! Conversion eff. 128→430nm 80±15% Reflector foils covered by TPB (under UV lamp) Optimization of The TPB layer thickness on the reflector P.Ot y u gova ( U n i Z H ) 2 Cryogenic PMTs. Nuclear recoil-like electron-like 2*104 events Improvement after including the fitting function! Pb210 source TPB coated reflectors. 50 Bq.
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