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.

30

30