XENON1T: opening a new era in the search for Dark Matter. Elena Aprile, Columbia University on behalf of the Collaboration, UCLA, February 17, 2016

Transcription

1 XENON1T: opening a new era in the search for Dark Matter Elena Aprile, Columbia University on behalf of the Collaboration, UCLA, February 17, 2016

2 The XENON Dark Matter Program XENON10 15 cm drift TPC - 25 kg XENON cm drift TPC kg ~10-43 cm 2 XENON1T/XENONnT 100 cm drift TPC kg/7000 kg ~10-45 cm 2 ~10-47 cm 2 / cm 2

3 The XENON Collaboration currently 130 scientists from 21 institutions

4 The XENON Collaboration currently 130 scientists from 21 institutions

5 The XENON Dark Matter Program Pioneering the Dual Phase Xe TPC to Search for Various Dark Matter Candidates XENON10 First Results Spin-dependent XENON days XENON100 DM-electron Modulation XENON Concept XENON R&D NR Scintillation in LXe ER/NR Discrimination XENON100 First Results XENON1T Start Spin independent Spin dependent Inelastic dark matter Light dark matter Axion Leptophilic DM Modulation Search XENON10 Inelastic DM XENON10 Light DM XENON days XENON100 Spin-dependent Axion search

6 2.8 Mar/11 May/11 Jul/11 Sep/11 Nov/11 Jan/12 Mar/12 (c) Level Meter 1 XENON100: low ER background as a probe for leptophilic dark matter Rate (counts/pe/tonne/day) Liquid Level [mm] Mean electronic recoil energy (kev) Radon Level [µbq/kg] Cut Acceptance Level Meter 2 DAMA/LIBRA annually modulated spectrum (2-6)keV interpreted as Radon inside LXe leptophilic DM, axial-vector coupling mirror DM XENON summer live days Mar/11 (d) May/11 Jul/11 Sep/11 Nov/11 Jan/12 Mar/ Mar/11 May/11 Jul/11 Sep/11 Nov/11 Jan/12 Mar/12 (e) Average Cut Acceptance 0.95 ± RMS/Mean kev % S1 (PE) 0.75 ± RMS/Mean 8.5% Phase [Days] -2log(L 1 /L max ) 0.65 Standard&DM&halo&phase&is&& 0.6 Mar/11 Ultra-low electron (f) May/11 Jul/11 Sep/11 Nov/11 Jan/12 Mar/12 recoil background in XENON100 (~155 x lower than 2.5 Single-scatter rate disfavored&by&2.5σ& kev DAMA/LIBRA 2 ± RMS/Mean average and ~2 x lower than Assuming&VeA&coupling&of&WIMPs& modulation amplitude) has 51% 1.5 allowed to exclude several leptophilic DM models invoked to explain DAMA 1 to&electrons,&dama/libra&annual& modulation signal. [XENON collaboration, Science 2015] 0.5 modulaoon&is&excluded&at&4.8σ& Excellent stability of XENON100 detector over more than one year enabled the first annual modulation test with the LXeTPC technology. No significant modulation found in electron recoil data [XENON collaboration, PRL 2015] -2log(L 1 /L max ) Amplitude [events/(kev tonne day)] Expected XENON100 95% C.L % C.L. best fit [Science , 851 (2015)] 9% [PRL 115, (2015)] Rate [Counts/Day] 0 Mar/11 May/11 Jul/11 Sep/11 Nov/11 Jan/12 Mar/12 Time arxiv: (Accepted into PRL) 3σ 2σ 1σ DAMA/LIBRA expected phase from DM halo σ 2σ 3σ

7 XENON100: data beyond the 225 live-days 150 days of new data acquired in New and improved analysis. Expect un-blinding next month. Final goal is to combine all XENON100 DM data ~500 live-days total to update current limits and perform a new annual modulation study In XENON100 was largely used to test: novel techniques for Rn removal internal calibration sources for XENON1T ( 220 Rn, 83m Kr, CH3T) response to low energy neutrons from an YBe source

8 New Internal Calibration Sources for Accurate Calibration of α, β & γ events, ER band & ER energy low-e 212 Pb in XE100 CH3T in XE100 see arxiv: Log10(S2/S1) Beta decay of 212Pb (from 220Rn) will provide frequent ER band calibration. 212Pb decays (half- live=11 hr) w/o need to remove it through getter like tritium CH3T (as shown by LUX) will give additional pure beta calibration of the ER band and more 9.4 kev from 83mKr will be used for a ER energy calibration 216Po convection map of XE100 S1 [pe] 83m Kr in XE100

9 The XENON1T Experiment XENON1T

10 The XENON1T Experiment XENON1T

11 The XENON1T Experiment Science goal: 100 x more sensitive than XENON100 after 2 ton- year exposure (see M. Selvi talk on sensitivity studies) Detector: two- phase XeTPC with 1 m drift gap and 2 ton active volume (3.5 ton total) viewed by 250 high QE - low radioactivity PMTs. Shielding: water Cherenkov muon veto. Cryogenic Plants: Xe cooling/purification/ distillation/storage systems designed to handle up to 10 ton of Xe. Upgrade to a larger detector planned for 2018 (see G.Plante talk on XENONnT ) Status: Construction/installation at LNGS in Hall B completed. All systems successfully tested and ready for operation. First light from TPC and MV PMTs recorded. DM search run projected to start by Summer XENON1T

12 XENON1T Systems Cryogenic and Purification LXe Detector Electronics and DAQ ReStoX and Kr-Column Muon Veto Detector

13 XENON1T Systems Cryogenic and Purification LXe Detector Electronics and DAQ ReStoX and Kr-Column Muon Veto Detector

14 Water Cherenkov Muon Veto Stainless steel tank with 700 m 3 of demineralized water 84 high QE PMTs (8 ) sensitive to Cherenkov light Internal surfaces covered with reflector film Efficiency in tagging muon events depends on PMT threshold and required number of PMT hits in coincidence E. Aprile et al., JINST 9 P11006 (2014) 10.5 m Expected efficiency in tagging muon induced neutrons (Monte Carlo studies): >99.7% for muons traversing the water tank (1/3 of muon events) > 71.4% for muons interacting in rock only (2/3 of muon events) 9.8 m Induced neutron background in 1 ton fiducial volume < 0.01 y - 1

15 XENON1T Muon Veto System Muon veto installation completed: foil, PMTs, electronics, DAQ First commissioning with water filling using our dedicated water plant: PMTs calibration, Trigger and DAQ, first muons detected

16 XENON1T Muon Veto System Muon veto installation completed: foil, PMTs, electronics, DAQ First commissioning with water filling using our dedicated water plant: PMTs calibration, Trigger and DAQ, first muons detected

17 XENON1T Individual optical fibers Muon Veto System Muon veto installation completed: foil, PMTs, electronics, DAQ First commissioning with water filling using our dedicated water plant: PMTs calibration, Trigger and DAQ, first muons detected

18 XENON1T Individual optical fibers Muon Veto System Muon veto installation completed: foil, PMTs, electronics, DAQ First commissioning with water filling using our dedicated water plant: PMTs calibration, Trigger and DAQ, first muons detected

19 Detector Cryostat & Support Platform a ultra-high-vacuum, thermally insulated system made of low-radioactivity material, to contain the detector with 3.5 tons of LXe at -95 C and 2 bar pressure and to couple it to the cryogenics system outside the water shield. Design: Optimized to simultaneously minimize mass while maximizing working pressure. Two independent cylindrical vessels. Outer vessel designed to contain a larger inner vessel for a more massive detector (XENONnT) A 7.5 m long umbilical carries independent inner pipes for PMT signals/hv cables and for Xe filling/recovery. Separate tube carries HV to to the detector via custom-designed UHV feedthrough.

20 Detector Cryostat & Support Platform a ultra-high-vacuum, thermally insulated system made of low-radioactivity material, to contain the detector with 3.5 tons of LXe at -95 C and 2 bar pressure and to couple it to the cryogenics system outside the water shield. Design: Optimized to simultaneously minimize mass while maximizing working pressure. Two independent cylindrical vessels. Outer vessel designed to contain a larger inner vessel for a more massive detector (XENONnT) A 7.5 m long umbilical carries independent inner pipes for PMT signals/hv cables and for Xe filling/recovery. Separate tube carries HV to to the detector via custom-designed UHV feedthrough.

21 Detector Cryostat & Support Platform a ultra-high-vacuum, thermally insulated system made of low-radioactivity material, to contain the detector with 3.5 tons of LXe at -95 C and 2 bar pressure and to couple it to the cryogenics system outside the water shield. Design: Optimized to simultaneously minimize mass while maximizing working pressure. Two independent cylindrical vessels. Outer vessel designed to contain a larger inner vessel for a more massive detector (XENONnT) A 7.5 m long umbilical carries independent inner pipes for PMT signals/hv cables and for Xe filling/recovery. Separate tube carries HV to to the detector via custom-designed UHV feedthrough.

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25 Cryogenic Plants Cryogenic System Purification System Cryogenic Pipe Cryostat Distillation Column ReStoX

26 Recovery and Storage of Xe (ReStoX) Goal: store up to 7600 kg of Xe in gaseous or liquid phase under high purity conditions fill Xe in ultra-high-purity conditions into detector vessel recover all the Xe from the detector, within a few hours, in case of emergency Method: Double walled, high pressure (72 bar) vacuum insulated sphere of 2.1 meter diameter, cooled by LN2 and by an internal LN-based condenser.

27 Recovery and Storage of Xe (ReStoX) Goal: store up to 7600 kg of Xe in gaseous or liquid phase under high purity conditions fill Xe in ultra-high-purity conditions into detector vessel recover all the Xe from the detector, within a few hours, in case of emergency Method: Double walled, high pressure (72 bar) vacuum insulated sphere of 2.1 meter diameter, cooled by LN2 and by an internal LN-based condenser.

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31 Xe Cooling System Goal: liquefy 3500 Kg of Xe and maintain the xenon in the cryostat in liquid form, at a constant temperature and pressure, and so for years without interruption. Redundant PTR Backup LN2 PTR Heat Exchangers Design goals: Stable temperature and pressure control Reliable, continuous, long term operation Resilience to unexpected failures High speed circulation with low additional heat load LXe circulation Vacuum insulation GXe flow to active cooling tower(s) LXe flow back to cryostat TPC PMT cables Connection to cryostat Main features: Redundant PTR cooling systems Backup LN2 cooling tower Efficient two-phase heat exchangers One PTR can be serviced while the other is in operation

32 Xe Cooling System Goal: liquefy 3500 Kg of Xe and maintain the xenon in the cryostat in liquid form, at a constant temperature and pressure, and so for years without interruption. Redundant PTR Backup LN2 PTR Heat Exchangers Design goals: Stable temperature and pressure control Reliable, continuous, long term operation Resilience to unexpected failures High speed circulation with low additional heat load LXe circulation Vacuum insulation GXe flow to active cooling tower(s) LXe flow back to cryostat TPC PMT cables Connection to cryostat Main features: Redundant PTR cooling systems Backup LN2 cooling tower Efficient two-phase heat exchangers One PTR can be serviced while the other is in operation

33 Cryogenic Distillation Column Goal: Active removal of Kr contamination in Xe. Natural Xe has Kr/Xe ~ with trace amounts of 85 Kr of 85 Kr/ Nat Kr ~ Principle: cryogenic distillation based on improved package column uses the 10 times higher vapor pressure of Kr w.r.t. Xe at -95 C to reach Nat Kr/Xe < 0.2 ppt. Diagnostics: Atom Trap Trace Analysis (Columbia) and Rare Gas Mass Spectroscopy (MPIK) Design parameters: Separation factor: Flow rate of 3kg/h -> whole XENON1T inventory can be purified within 6 weeks 99% Xenon recovery Commissioning of the distillation column on XENON1T 5m First results with distillation test facility (phase 1: 1m package material): Purified liquid out: Nat Kr/Xe < ppt (90% c.l.) A factor ~10 better than required for XENON1T! Measured with GC-RGMS system at MPIK (S. Lindemann & H. Simgen, Eur. Phys. C 74 (2014) 2746): only a limit could be set! Alternative measurements by ATTA (E. Aprile et al., Rev. Sci. Instr. 84 (2013) ) Reference: S. Rosendahl et al., JINST 9 (2014) P10010 S. Rosendahl et al., Rev. Sci. Instr. 86 (2014) E. Brown et al., JINST 8 (2013) P hours of continuous distillation, 210 kg processed! Thermodynamic stability under design parameters demonstrated! Separation factor > demonstrated by GC-RGMS (MPIK)

34 Time Projection Chamber Design Goal: realize a ultra-low-background two-phase XeTPC with the best performance for WIMP detection. Largely influenced by the lessons learnt with XENON100 and R&D on new technologies and measurements with the XENON1T Demonstrator and other facilities. The XENON1T detector is the first TPC with ~1 m drift in LXe and uses a total of ~3500 kg of ultra high purity LXe. XENON1T Demonstrator Field Simulations PTFE Reflectivity: High voltage feedthrough Cables and Connectors: Field Simulations Grids Fabrication and Testing PMTs and HV dividers Testing TPC Mechanical Design

35 Liquid xenon inlet/outlet pipes custom-made high voltage feedthrough: cathode bias in the range 50 ~ 100 kv Top array: 127 PMT in radial pattern. Diving bell Screening mesh: etched, =178 µm The TPC is mechanically supported by 24 PTFE pillars, connecting a steel ring on the top with a copper ring on the bottom. Anode: etched mesh =178 µm Gate grid: etched mesh =127 µm LXe level: measured by 2 long and 4 short levelmeters TPC electric field: generated between cathode ( HV) and gate grid (0V) 74 shaping electrodes (OFHC Copper) connected via 2 chains of high-ohmic resistors Interlocking PTFE reflectors Cathode: single wires =216 µm TPC electrode frames: low-background stainless steel Bottom array: 121 PMTs in tight, hexagonal pattern screening grid: single wires =216 µm

36 Liquid xenon inlet/outlet pipes custom-made high voltage feedthrough: cathode bias in the range 50 ~ 100 kv Top array: 127 PMT in radial pattern. Diving bell Screening mesh: etched, =178 µm The TPC is mechanically supported by 24 PTFE pillars, connecting a steel ring on the top with a copper ring on the bottom. Anode: etched mesh =178 µm Gate grid: etched mesh =127 µm LXe level: measured by 2 long and 4 short levelmeters TPC electric field: generated between cathode ( HV) and gate grid (0V) 74 shaping electrodes (OFHC Copper) connected via 2 chains of high-ohmic resistors Interlocking PTFE reflectors Cathode: single wires =216 µm TPC electrode frames: low-background stainless steel Bottom array: 121 PMTs in tight, hexagonal pattern screening grid: single wires =216 µm

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39 Photomultipliers High QE (average 34%), low-radioactivity, 3 PMT (R ) developed for XENON1T, in close collaboration with Hamamatsu to select cleanest materials. Tested stability in LXe. Each PMT has been screened for radioactivity and tested at room T and low T 7 1) Quartz: faceplate (PMT window) Cs 2) Aluminum: sealing 0 Co 40 K 8 Th 8 Ra 6 Ra 38 U Relative contribution [%] 3) Kovar: Co-free body 4) Stainless steel: electrode disk 5) Stainless steel: dynodes 6) Stainless steel: shield 7) Quartz: L-shaped insulation 8) Kovar: flange of faceplate 9) Ceramic: stem 10) Kovar: flange of ceramic stem 11) Getter 22

40 Readout Electronics and Data Acquisition Features Triggerless readout at ⅓ p.e. Software trigger, flexible algorithms High rates up to 1 khz (300 MB/s) for external calibration Technology web data browser Off the shelf electronics (incl. CAEN digitizers w/ custom firmware) MongoDB: high speed data-buffering and fast trigger queries Web frontend (Django) for system control and online data monitoring Status: Installed at LNGS In use for detector commissioning DAQ installation at LNGS

41 Radon Control Select construction materials with low radon ( 222 Rn) emanation rate. Implement measures to further reduce 222 Rn (alternative materials, surface cleaning procedures, etc.) Quantify and locate remaining 222 Rn sources Sample.

42 Radon Measurement

43 Slow Control System Goal: safely and securely operate and monitor the experiment; record all its operating parameters. Industrial process control hardware and software used to provide high reliability. Fully developed and tested. Local and remote control and monitoring, alarms, parameter recoding are operational and are used in commissioning. The Cryogenic system touch panel Local Control Station with an industrial Programmable Automation Controller (PAC) and its IO modules Display of historical values Central system user interface showing the ReStoX control panel

44 XENON1T sensitivity XENON Collaboration: arxiv: With XENON1T, 2 t*y, minimum cross section: σ = cm m = 50 GeV/c 2 Improvement by an order of magnitude with XENONnT, 20 t*y.

45 XENON1T Sensitivity vs Exposure

46 Summary Liquid Xenon detectors continue to lead the field of direct detection. With XENON1T we begin a new phase with the technology of two- phase XeTPC pushed to a new limit. The challenges we meet and the solutions we invent will inform future efforts. The experiment will start data- taking in a few months. It will be the most sensitive direct detection search worldwide for several years, considering the upgrade to a new detector with more than twice the mass by XENON1T will take data at the same time as the LHC Run 2 and several indirect searches. The complementarity of the three approaches is critical to either discover or rule out WIMPs as Dark Matter in the next few years.

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