XENON1T: opening a new era in the search for Dark Matter Elena Aprile, Columbia Universityon behalf of the Collaboration, UCLA, February 17, 2016
XENON10 15 cm drift TPC - 25 kg
~10-43 cm2
XENON100 30 cm drift TPC - 161 kg
2005-2007 2007-2015 2012-2022
XENON1T/XENONnT 100 cm drift TPC - 3500 kg/7000 kg
The XENON Dark Matter Program
~10-45 cm2 ~10-47 cm2 / 10-48 cm2
currently 130 scientists from 21 institutions
The XENON Collaboration
currently 130 scientists from 21 institutions
The XENON Collaboration
2001 2003 2005 2007 2009 2011 2013 2015
XENON Concept
XENON10 First Results
Spin-dependent
XENON R&D NR Scintillation in LXe ER/NR Discrimination
XENON10 Inelastic DM
XENON100 First Results
XENON10 Light DM
XENON100 100 days
XENON100 225 days
XENON100 Spin-dependent Axion search
XENON100 DM-electron Modulation
XENON1T Start
The XENON Dark Matter Program Pioneering the Dual Phase Xe TPC to Search for Various Dark Matter Candidates
• Spin independent • Spin dependent • Inelastic dark matter • Light dark matter • Axion • Leptophilic DM • Modulation Search
• Ultra-low electron recoil background in XENON100 (~155 x lower than DAMA/LIBRA average and ~2 x lower than modulation amplitude) has allowed to exclude several leptophilic DM models invoked to explain DAMA modulation signal. [XENON collaboration, Science 2015]
• 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]
S1 (PE)0 5 10 15 20 25 30
Rat
e (c
ount
s/PE
/tonn
e/da
y)
0
2
4
6
8
10
12
Mean electronic recoil energy (keV)1 2 3 4 5 6 7 8 9 10
DAMA/LIBRA annually modulated spectrum (2-6)keV interpreted asleptophilic DM, axial-vector couplingmirror DMXENON100 70 summer live days
XENON100: low ER background as a probe for leptophilic dark matter
• Unbinned&PL&analysis&&of&ER&data&assuming&&periodic&signal&&hypothesis&(&&&1)&
• Compare&to&maximum&likelihood&(&&&max),&&fixing&period&to&1&year&
Probing&Annual&ModulaOon&in&XENON100&
August&5,&2015& Patrick&de&Perio&@&DPF2015:&XENON&Enlightening&the&Dark& 9&
Phase [Days]20 40 60 80 100 120 140 160 180 200A
mpl
itude
[eve
nts/
(keV
·tonn
e·da
y)]
0
2
4
6
8
10
12 Expected
expectedphase fromDM halo
XENON10095% C.L.99.73% C.L.best fit
20 40 60 80 100 120 140 160 180 200
24681012
σ1
σ2
σ3
2 4 6 810120
2
4
6
8
10
12
σ1 σ2 σ3
-2lo
g(L 1/L
max
)
-2log(L1/Lmax)
DAMA/LIBRA
• Standard&DM&halo&phase&is&&disfavored&by&2.5σ&
• Assuming&VeA&coupling&of&WIMPs&to&electrons,&DAMA/LIBRA&annual&modulaOon&is&excluded&at&4.8σ&
Mar/11 May/11 Jul/11 Sep/11 Nov/11 Jan/12 Mar/12
Pres
sure
[bar
]
2.215
2.22
2.225
2.23
2.235
2.24 Xenon Gas Pressure (a)
Mar/11 May/11 Jul/11 Sep/11 Nov/11 Jan/12 Mar/12
C]
oT
[∆
-0.15-0.1
-0.050
0.050.1
0.150.2
0.250.3
CoT(Room) avg:20.7∆×-110CoT(Gas Xenon) avg:-86.5∆
CoT(Liquid Xenon) avg:-91.6∆
(b)
Mar/11 May/11 Jul/11 Sep/11 Nov/11 Jan/12 Mar/12
Liqu
id L
evel
[mm
]
2.3
2.4
2.5
2.6
2.7
2.8Level Meter 1Level Meter 2
(c)
Mar/11 May/11 Jul/11 Sep/11 Nov/11 Jan/12 Mar/12
Bq/
kg]
µR
adon
Lev
el [
50
60
70
80
90
100 (d)
RMS/Mean±8.5%
9%
Radon inside LXe
Mar/11 May/11 Jul/11 Sep/11 Nov/11 Jan/12 Mar/12
Cut
Acc
epta
nce
0.60.65
0.70.75
0.80.85
0.90.95
1 (e)RMS/Mean±3.9%
Average Cut Acceptance2.0 - 5.8 keV
TimeMar/11 May/11 Jul/11 Sep/11 Nov/11 Jan/12 Mar/12
Rat
e [C
ount
s/D
ay]
0
0.5
1
1.5
2
2.5(f)
RMS/Mean±51%
Single-scatter rate 2.0 - 5.8 keV
arXiv:1507.07748 (Accepted into PRL)
[Science 349, 851 (2015)] [PRL 115, 091302 (2015)]
• 150 days of new data acquired in 2013-14. 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 2014-15 XENON100 was largely used to test:
• novel techniques for Rn removal
• internal calibration sources for XENON1T (220Rn, 83mKr, CH3T)
• response to low energy neutrons from an YBe source
XENON100: data beyond the 225 live-days
216Po convection map of XE100
low-E 212Pb in XE100
New Internal Calibration Sources for Accurate Calibration of α−, β− & γ−events, ER band & ER energy
Log 1
0(S2/
S1)
S1 [pe]
CH3T in XE100
83mKr in XE100
see arXiv:1602.01138
• 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
The XENON1T Experiment
XENON1T
The XENON1T Experiment
XENON1T
The XENON1T Experiment
XENON1T
• 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 2016.
XENON1T Systems
LXe Detector
Cryogenic and Purification
Electronics and DAQ
ReStoX and Kr-Column
Muon Veto Detector
XENON1T Systems
LXe Detector
Cryogenic and Purification
Electronics and DAQ
ReStoX and Kr-Column
Muon Veto Detector
• Stainless steel tank with 700 m3 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
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)
Induced neutron background in 1 ton fiducial volume < 0.01 y-‐1
E. Aprile et al., JINST 9 P11006 (2014)
10.5 m
9.8 m
Water Cherenkov Muon Veto
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
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
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
Individual optical fibers
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
Individual optical fibers
Detector Cryostat & Support Platforma 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.
Detector Cryostat & Support Platforma 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.
Detector Cryostat & Support Platforma 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.
Cryogenic Plants
Distillation Column ReStoX
Cryostat
Cryogenic Pipe
Cryogenic System
Purification System
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.
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.
Xe Cooling SystemGoal: 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
Heat Exchangers
LXe flow backto cryostat
GXe flow to active cooling tower(s)
Vacuum insulation
LXe circulation
Connection to cryostat
TPC PMT cables
PTRDesign goals: ● Stable temperature and pressure control● Reliable, continuous, long term operation● Resilience to unexpected failures● High speed circulation with low
additional heat load
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
Xe Cooling SystemGoal: 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
Heat Exchangers
LXe flow backto cryostat
GXe flow to active cooling tower(s)
Vacuum insulation
LXe circulation
Connection to cryostat
TPC PMT cables
PTRDesign goals: ● Stable temperature and pressure control● Reliable, continuous, long term operation● Resilience to unexpected failures● High speed circulation with low
additional heat load
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
Cryogenic Distillation Column
5m
Goal: Active removal of Kr contamination in Xe. Natural Xe has Kr/Xe ~ 10-9 – 10-6 with trace amounts of 85Kr of 85Kr/NatKr ~ 10-11Principle: 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 NatKr/Xe < 0.2 ppt.Diagnostics: Atom Trap Trace Analysis (Columbia) and Rare Gas Mass Spectroscopy (MPIK)
Commissioning of the distillation column on XENON1T
• 70 hours of continuous distillation, 210 kg processed!
• Thermodynamic stability under design parameters demonstrated!
• Separation factor >100.000 demonstrated by GC-RGMS (MPIK)
Design parameters: ● Separation factor: 104 – 105● Flow rate of 3kg/h -> whole XENON1T
inventory can be purified within 6 weeks● 99% Xenon recovery
First results with distillation test facility (phase 1: 1m package material):
● Purified liquid out: NatKr/Xe < 0.026 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) 093105)
Reference: ● S. Rosendahl et al., JINST 9 (2014) P10010● S. Rosendahl et al., Rev. Sci. Instr. 86 (2014) 115104● E. Brown et al., JINST 8 (2013) P02011
Time Projection ChamberDesign 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
Bottom array: 121 PMTs in tight, hexagonal pattern
LXe level: measured by 2 long and 4 short levelmeters
Cathode: single wires ∅=216 µm
screening grid: single wires ∅=216 µm
Gate grid: etched mesh ∅=127 µm
Anode: etched mesh ∅=178 µm
Screening mesh: etched, ∅=178 µm
Interlocking PTFE reflectors
TPC electrode frames: low-background stainless steel
Liquid xenon inlet/outlet pipes
Diving bell
Top array: 127 PMT in radial pattern.
TPC electric field: generated between cathode (–HV) and gate grid (0V)74 shaping electrodes (OFHC Copper) connected via 2 chains of high-ohmic resistors
The TPC is mechanically supported by 24 PTFEpillars, connecting a steel ring on the top with a copper ring on the bottom.
custom-made high voltage feedthrough: cathode bias in the range –50 ~ 100 kV
Bottom array: 121 PMTs in tight, hexagonal pattern
LXe level: measured by 2 long and 4 short levelmeters
Cathode: single wires ∅=216 µm
screening grid: single wires ∅=216 µm
Gate grid: etched mesh ∅=127 µm
Anode: etched mesh ∅=178 µm
Screening mesh: etched, ∅=178 µm
Interlocking PTFE reflectors
TPC electrode frames: low-background stainless steel
Liquid xenon inlet/outlet pipes
Diving bell
Top array: 127 PMT in radial pattern.
TPC electric field: generated between cathode (–HV) and gate grid (0V)74 shaping electrodes (OFHC Copper) connected via 2 chains of high-ohmic resistors
The TPC is mechanically supported by 24 PTFEpillars, connecting a steel ring on the top with a copper ring on the bottom.
custom-made high voltage feedthrough: cathode bias in the range –50 ~ 100 kV
22
Photomultipliers• High QE (average 34%) , low-radioactivity, 3” PMT (R11410-21) 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
Low radioactivity PMT for XENON1TMain PMT parts screened separatelySelection of low radioactivity materialsfor XENON1TPMT fulfils background requirementsMajor contributor to radioactivityidentified: the ceramic stem
XENON collaboration, arxiv:1503.07698
Relative contribution [%]0 10 20 30 40 50 60 70 80 90 100
U238
Ra226
Ra228
Th228
K40
Co60
Cs137 1) Quartz: faceplate (PMT window)2) Aluminum: sealing3) Kovar: Co-free body
4) Stainless steel: electrode disk5) Stainless steel: dynodes
6) Stainless steel: shield7) Quartz: L-shaped insulation8) Kovar: flange of faceplate
9) Ceramic: stem10) Kovar: flange of ceramic stem
11) Getter
Low radioactivity PMT for XENON1TMain PMT parts screened separatelySelection of low radioactivity materialsfor XENON1TPMT fulfils background requirementsMajor contributor to radioactivityidentified: the ceramic stem
XENON collaboration, arxiv:1503.07698
Relative contribution [%]0 10 20 30 40 50 60 70 80 90 100
U238
Ra226
Ra228
Th228
K40
Co60
Cs137 1) Quartz: faceplate (PMT window)2) Aluminum: sealing3) Kovar: Co-free body
4) Stainless steel: electrode disk5) Stainless steel: dynodes
6) Stainless steel: shield7) Quartz: L-shaped insulation8) Kovar: flange of faceplate
9) Ceramic: stem10) Kovar: flange of ceramic stem
11) Getter
Installation of PMTs in the arrays
Features
● Triggerless readout at ⅓ p.e. ● Software trigger, flexible algorithms ● High rates up to 1 kHz (300 MB/s) for
external calibration
Technology
● 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
web data browser
DAQ installation at LNGS
Status: ● Installed at LNGS ● In use for detector commissioning
Readout Electronics and Data Acquisition
Radon Control• Select construction materials with low radon (222Rn) emanation rate.• Implement measures to further reduce 222Rn (alternative materials, surface cleaning procedures, etc.)• Quantify and locate remaining 222Rn sources
• Sample.
Radon Measurement
• 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
Display of historical values
Slow Control System
Local Control Station with an industrial Programmable Automation Controller (PAC) and its IO modules
Central system user interface showing the ReStoX control panel
XENON1T sensitivity
With XENON1T, 2 t*y, minimum cross section: σ = 1.6 10-‐47 cm2 @ m = 50 GeV/c2 Improvement by an order of magnitude with XENONnT, 20 t*y.
XENON Collaboration: arXiv:1512.07501
XENON1T Sensitivity vs Exposure
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 2018.
• 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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