Status of the ArDM experiment Filippo Resnati (ETH Zurich) on behalf of the ArDM Collaboration LIDINE 2013, FNAL, 29-31 May 2013
Collaboration •ETH Zurich • A. Badertscher, F. Bay, C. Cantini, A. Curioni, U. Degunda, S. Di Luise, A. Gendotti, S. Horikawa, L. Knecht, D. Lussi, S. Murphy, G. Natterer, K. Nguyen, L. Periale, F. Resnati, A. Rubbia, F. Sergiampietri, D. Sgalaberna, T. Viant, S. Wu •CIEMAT • M. Daniel, B. Montes, L. Romero, R. Santorelli Filippo Resnati - LIDINE 2013, FNAL, 30 May 2013 2
Outline •Argon as a target for WIMP direct detection •ArDM recent past • Pulse shape discrimination (old runs) • Material screening • Neutron background and passive shielding •Status of the detector • New TPB coating performance • Installation of the detector in Canfranc • First test in warm GAr underground and expected light yield •Conclusions and outlooks Filippo Resnati - LIDINE 2013, FNAL, 30 May 2013 3
Argon as target • Extensive experience as Xe detector medium Kr (neutrino experiments). Ar • Cheap, easy to handle and to Ne purify (large volumes). • Event rate less sensitive to energy threshold than for heavier noble gasses. • PSD and charge/light (ß/ γ background rejection). • 39 Ar in atmosphere (ß-active isotope, T 1/2 = 269 y, Fast component Slow component Q = 565 keV, ~1 Hz/kg). Filippo Resnati - LIDINE 2013, FNAL, 30 May 2013 4
Direct WIMP detection with double phase TPC • WIMPs (elastic) scatters on Ar nuclei. • Nuclear recoils (<200 keV) excite and ionize surrounding argon atoms. GAr • Detection of scintillation light: LAr • VUV (~128 nm) photons + WLS + PMTs. • Detection of ionized charge: • e- drift + extraction to the vapor + proportional scintillation. • charge can be amplified in gas and directly readout (LEM). Filippo Resnati - LIDINE 2013, FNAL, 30 May 2013 5
ArDM - ~1 ton double phase argon TPC for direct DM searches. - Presently installed in the Laboratorio Subterráneo de Canfranc. - Drift length: 120 cm. E. Aprile et al , Phys.Rev.Lett. 109 (2012) 181301 - Diameter: 80 cm. - Target mass: 850 kg. - Neutron shielding: passive polyethylene. - Argon purification: LAr and GAr recirculation through getters. - Temperature control: vacuum insulation + two cryo-coolers. - Light readout: 12 PMTs in LAr + 12 PMT in GAr (8“ Hamamatsu R5912-02MOD-LRI). - Charge readout: proportional scintillation in vapor (eventually 30 keV er threshold Large Electron Multiplier). 0.5 ev/ton/day A. Rubbia, J. Phys.: Conf. Ser., vol. 39, pp. 129–132, 2006 Filippo Resnati - LIDINE 2013, FNAL, 30 May 2013 6
Phased approach • Surface operation: • Build and assemble the ArDM prototype (extensive R&D efforts). • Commission the detector cryogenics, purification, HV, electronics, light readout and software. • Underground operation I: • Construction and installation of the passive neutron shielding. • Installation of ArDM and its infrastructures (finished in March 2013). • Warm gas argon runs (test light readout system) - ongoing. • Cold gas argon runs (test cryogenics, light readout, impact on the lab environment, ...). • Underground operation II: • Liquid argon tests (commission HV, purification, cryogenics, ...). • Physics runs (beginning 2014). Filippo Resnati - LIDINE 2013, FNAL, 30 May 2013 7
Pulse shape discrimination LAr run on surface with only 14 PMT array below the cathode 241 Am-Be source (externally triggered tagging the γ with a NaI) Fast Slow O(10 ns) O(1.6 μ s) PSD parameter is the component ratio: fast/(fast+slow) neutron neutron -> “fast” ß/ γ -> “slow” gamma Filippo Resnati - LIDINE 2013, FNAL, 30 May 2013 8
Pulse shape discrimination 90 0.9 CR_Histo_2D CR_Histo_2D 241 Am-Be 80 Entries Entries 48813 48813 0.8 Mean x Mean x 192.2 192.2 n - neutrons: < 11 MeV Mean y Mean y 0.426 0.426 70 0.7 RMS x RMS x 257.6 257.6 (max Ar recoil ~1 MeV) component ratio RMS y RMS y 0.2043 0.2043 60 0.6 - γ : 4.4 MeV 50 0.5 40 0.4 30 0.3 1 MeV re ~ 175 p.e. 20 0.2 @ 0.7 p.e./keV ee γ 10 0.1 0 0 200 400 600 800 1000 total collected light (p.e .) 1600 1800 Entries 30216 Entries 30216 Entries 18776 Entries 18776 241 22 Am-Be source Na source 1400 22 Na 241 Am-Be 1600 after background subtr action after background subtr action 1200 1400 fit (gaussian and sum o f fit (gaussian and expon ential 1200 1000 counts/bin counts/bin function) exp. and gaussian func tion) 1000 800 800 600 600 400 400 200 200 0 0 0 0.2 0 .4 0.6 0 .8 1 0 0.2 0 .4 0.6 0 .8 1 component ratio component ratio Filippo Resnati - LIDINE 2013, FNAL, 30 May 2013 9
Pulse shape discrimination Measured fraction of 22 Na source events mis-identified as neutron. Natural and cosmic induced measured electronic recoil contamination -1 10 background biases the contribution from the photoelectron statistics (ArDM average pulse shape) measure -> to be evaluated electronic recoil contamination contribution from the photoelectron statistics -2 10 (pulse shape from W. Lippincott, et al.) underground -3 10 -4 Light yield estimated for the 10 present configuration: -5 10 2 p.e./keV ee -6 10 Contamination expected: -7 O(10 -3 ) @ 10 keV ee 10 (statistical fluctuation only) 0 20 40 60 80 100 120 140 160 total collected light (p.e.) Additional rejection factor from charge to light ratio (measure foreseen during the underground operation) Filippo Resnati - LIDINE 2013, FNAL, 30 May 2013 10
Material screening Cryogenic and low activity Hamamatsu R5912-02MOD-LRI Filippo Resnati - LIDINE 2013, FNAL, 30 May 2013 11
Material screening Measurement campaign with Ge detector supported by the LSC Already measured: Raw gamma spectrum - PMT (glass / dynodes / base) - Drift cage resistors Measurement foreseen: - Stainless steel of the vessel - Parts of the field cage 10 -12 n/s/cm 3 Simulation (SOURCES) Contaminations are input to of 1 ppb 238 U in stainless evaluate the neutron flux steel inside the detector (irreducible background) -> Ongoing Filippo Resnati - LIDINE 2013, FNAL, 30 May 2013 12
Neutron background in the cavern In collaboration with Nuclear Innovation Unit (CIEMAT) “External” sources of neutrons: Neutron flux and energy spectrum - Natural isotopes (spontaneous “before the shielding” are essential fissions and ( α ,n) reactions) input parameters for the complete - cosmic muon Monte Carlo simulation (spallation reactions) Detector tested at CIEMAT and to be moved in LSC 252 Cf liquid scintillator BC501A Filippo Resnati - LIDINE 2013, FNAL, 30 May 2013 13
Passive shielding - 50 cm thick polyethylene shield reduces the flux of neutron below 1 MeV by a factor of ~10 5 - Evaluate neutron interaction rate in ArDM -> need of the measurement of the neutron flux in the cavern (ongoing) - Lateral shield partially installed (allow to work on the top flange). - Bottom shield ready to be shipped to LSC. - Top shield assembled in CIEMAT (load test ongoing). Filippo Resnati - LIDINE 2013, FNAL, 30 May 2013 14
New Vs Old coatings Evaporated TPB requires careful handling, minimize exposure to UV light and air TPB very good WLS solution for LAr applications. R&D to chemically attach it on Makrolon (paper in preparation) 1000 # p.e. 900 800 24 PMTs and reflectors re-coated. New 700 Test in warm GAr with a 241 Am α source. 600 Comparison of the same PMT before and 500 400 after the re-coating. 300 Detection efficiency improvement: ~5x. 200 Old 100 0 0 500 1000 1500 2000 2500 3000 3500 4000 τ 3 (ns) Filippo Resnati - LIDINE 2013, FNAL, 30 May 2013 15
Installation (PMTs) PMTs coated and tested at CERN mounted at ETH (Zurich). TPB 0.1-0.2 mg/cm 2 PMT layout PMT independently mounted Completed PMT array (Zurich) In the boxes ready to be shipped Filippo Resnati - LIDINE 2013, FNAL, 30 May 2013 16
Installation (reflectors) Side reflectors prepared at CERN and coated at IFIC (Valencia). Tetratex sewed on Vikuiti Unpacking (LSC) Evaporator (Valencia) TPB ~1 mg/cm 2 Filippo Resnati - LIDINE 2013, FNAL, 30 May 2013 17
Mounting the detector March 2013 Filippo Resnati - LIDINE 2013, FNAL, 30 May 2013 18
First GAr test underground Measurement of the light yield of the newly coated detector fully assembled Short α track - 9 days of data-taking (~5 h/day) Long α track - GAr (99.9999% pure) filling and evacuation every day. Mylar sealed 241 Am source (~500 Bq) custom made at CIEMAT installed in the active volume of ArDM. - ~5 MeV α @ 100 Hz in the active volume. - 60 keV γ @ ~1 Hz in the active volume. α events well localized: - Z coordinate scan with the source facing downwards. Filippo Resnati - LIDINE 2013, FNAL, 30 May 2013 19
Electronics - VME based electronics. - CAEN crate and modules including 4x ADC V1720, 8ch, 12bit, 2Vpp, 250MS/s. Trigger on the coincidence of the top and bottom PMT arrays with a threshold of 1.75 p.e. 12x 12x Passive Analog Threshold Coinc. PMTs splitter sum discr. unit 12x 12x 12x 12x PC Timing ADCs & unit storage Filippo Resnati - LIDINE 2013, FNAL, 30 May 2013 20
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