XENONnT and purity monitor S. Moriyama (ICRR & Kavli-IPMU, The Univ. of Tokyo) on behalf of the XENON collaboration March 21, 2019, active media TPC workshop @Kobe , Japan 1
Scientific Importance of detection of dark matter Understanding the nature of dark matter is one of the most important issues in the particle astrophysics. Strong evidence on dark matter: Cluster of galaxies, rotation curve of galaxies, lensing effect, large scale structure, cosmic microwave background, etc. Identification of dark matter must be a breakthrough in understanding the universe filled with “unknowns”. 2
The XENON collaboration ~170 collaborators 27 institutions 3
XENON program Liquid xenon: scalable for sensitive WIMP dark matter search. Dual phase: 3D TPC, excellent separation of e/n recoils. Low energy thre.: ~5 keV nr and lower for electron recoils because of high light yield XENON10 XENON100 XENON1T XENONnT Total Xe: 25 kg Total Xe: 162 kg Total Xe: 3.2 ton Total Xe: ~8.4 ton Target: 14 kg Target: 62 kg Target: 2 ton Target: 5.9 ton Fiducial: 5.4 kg Fiducial: 34/48 kg Fiducial: 1.3 ton Fiducial: ~4 ton Limit: ~10 -43 cm 2 Limit: ~10 -45 cm 2 Limit: ~10 -47 cm 2 Limit: ~10 -48 cm 2 2005 2010 2015 2020 4
Experimental site LNGS Gran Sasso National Laboratory, Italy Depth: 3,600 m water equiv. diameter 9.6 m x 10 m water Cherenkov shield 5
Dual phase LXe detector S1 and S2: Energy & particle identification Drift time: Z position Photon distribution of S2: X&Y position determination Electrons from ionization Energy deposition in TPC extracted into the gas phase causes scintillation light and amplified: S2. S1 in liquid xenon target 6
Results from XENON1T ) 8 0 0 2 ( 0 1 N O N E Phys. Rev. Lett. X 10 − 43 121, 111302 (2018) WIMP-nucleon σ SI [cm 2 ] 10 − 44 6 ) 1 0 2 ( 0 0 1 N O N E 1.0 t year X (1.3 ton, 278.8 d) 10 − 45 PandaX-II (2017) LUX (2017) ) k r o w s i h 10 − 46 t r , Electron Recoil BG y t × 1 ( T 1 N O 5 N E X 82 � � 3/t yr keV ee ) n o i c t 3 e j o 10 − 47 r P ~ 2.2x10 -4 /kg d keV ee r a e y t 0 2 ( T n N O N E X t m i i l y r e v o c s i d 10 − 48 o n i r t u e n 99.7% ER rejection 3 , 1 0 2 d r a l l B i 7 1 0 2 i h c s a n g a B 10 − 49 4.1x10 -47 cm 2 10 1 10 2 10 3 @ 30 GeV, 90% C.L. WIMP mass [GeV/c 2 ] XENON1T is the world’s most sensitive experiment! 7
Toward discovery: XENONnT ) 8 0 0 2 ( 0 1 N O N E X One order of magni- 10 − 43 WIMP-nucleon σ SI [cm 2 ] tude higher sensitivity 10 − 44 6 ) 1 0 2 ( 0 0 1 N O N E X 20 t year (x20) 10 − 45 PandaX-II (2017) (~ 4 ton x 5 yrs) ������������ LUX (2017) ) k r o w s i h 10 − 46 t r , y t × 1 Background (x~1/10) ( T 1 N O N E X ) n o i c t e j o 10 − 47 r P r a e y t 0 2 ( ~2x10 -48 cm 2 (x~1/10) T n N O N E X t m i i l y r e v o c @ 30 GeV, 90% C.L. s i d 10 − 48 o n i r t u e n 3 , 1 0 2 d r a l l B i 7 1 0 2 i h c s a n g a B Construction ongoing. 10 − 49 Commissioning 10 1 10 2 10 3 WIMP mass [GeV/c 2 ] started last year! Larger Exposure, lower BG, improved performance! 8
XENONnT upgrade: overview Target Size Lower BG: Radon Central detector: Rn distillation larger TPC, 494 PMTs will be added LXe purification Lower BG: Neutron veto & purity monitor tags radiogenic neutrons will be added XENON1T stopped and construction already started 9
Target size: Larger TPC XENON1T XENONnT Active target mass Existing/tested/being prepared: 2 ton à 5.9 ton mu cr Fiducial mass out 1.3 ton à ~4 ton expected in LX The outer cryostat cr 1.4m will be extended. pur Large TPC is being built. K D The number of PMTs 1.4m sl is doubled. cal Storage for larger amount > of liquid xenon is added. 230 Liquid phase Xe 2 purification is being added. ma 2012-2018 2019-2023 Drift time > 1 ms 10
Target size: TPC, PMT array, DAQ TPC size: 1.33 m f x 1.48 m: TPC electrode wiring is ongoing. PMT test completed: 494 PMTs incl. PMTs from XENON1T DAQ and electronics: Doubling channels + add. for 0 nbb 11
Target size: LXe storage XENON1T: ReStoX XENONnT: + ReStoX2 Capacity 7.6 ton of Xe Capacity 10 ton of Xe Vacuum insulated Foam insulated Max. pressure 73 bar. Max. pressure 71.5 bar Fast recovery (~50 kg/h) Very fast recovery (~1 t/h) with Xe freezing ~8000 kg of LN2 consumption for recovery Cleaning inside (water removal) completed and Kr distillation already started to add more xenon. 12
LXe purification & purity monitor Xe purification to remove electro- negative impurities is crucial to realize good performance Filter of dual phase detectors. GXe purification ~120 slpm, = 1 t/d with minor modifications Faster purification necessary LXe purification ~5 L/min = 21 t/d Filter: two custom Purity regeneratable monitor cryogenic O 2 filters LXe pump 2Cu+O 2 à 2CuO >1 ms electron Direct extraction of LXe from lifetime necessary the bottom of the detector. 13
Electronegative impurities Electronegative impurities capture drift electrons and reduce S2 signals. If their effect is not well corrected, the resolution of S2 and rejection efficiency are degraded. Projected cS2 Correct corrections S2 Z To make best PID perform- cS2 ance, corrected S2 needs to Z be constant = best resolution Projected Wrong after projection. corrections Z 14
Preamp output (average of 100 wave anode Anode In the purity monitor electrons produced by flashing a xenon lamp onto a photocathode (Au) are drifted by E field. Induction at the Monitoring LXe purity is important to correct the loss during drift. 15 Drift time ( µ s) 100 waveforms) Preamp output Cathode Cathode (average of Drift time LXe purity monitor measure the loss of electrons on the path. cathode and the anode enable us to if it w
Development of purity monitor Goal Determination of electron life ~10% accuracy @ 1ms Electric field calculation by COMSOL. 1 st trial Electric field started from the cathode 2050V Anode grid Cathode 0V grid 50V Cathode 2550V Anode Drift length: 200 mm Encapsulated in ICF117 standard tube. Smaller gaps make E field contained. 16
Impact of tilt 2 nd trial Smaller A small tilt of electrodes cause Larger gaps gaps large loss of electric field. Making gaps between electrodes minimizes its impact. E field from a larger part of the photocathode reaches the anode. Photocathode 17
Grid transparency Final design Cathode 0V Cathode -80V A larger diameter is Cathode grid 0V Cathode grid 0V more robust for tilt. An optimized potential gives a better grid transparency. 18 All E field lines pass Some E field lines hit grid
Development of purity monitor Cleaning parts before installation is important to minimize contaminations. Soldering à fixing chip resistors using PTFE plate and screws. Gap 2 mm, ring 10 mm thick, inner diameter 38 mm. 19
Development of purity monitor 550 L of xenon, 5.5 liter/min 204 mm of drift length, 100 V/cm drift field 20
Result After ~80 hrs of operation we Achieved ~3 ms electron life time. Fluctuation of data points ~10 % @~3 msec This satisfies our goal. Origin of systematic errors being investigated. 21
Summary • XENONnT is designed XENON10 (2008) to explore dark matter 10 − 43 particles with WIMP-nucleon σ SI [cm 2 ] 10 − 44 XENON100 (2016) unprecedent sensitivity. • Technical challenges in 10 − 45 PandaX-II (2017) ) 7 1 0 XENON1T (1 t × yr, this work) 2 ( X U a larger TPC and large L 10 − 46 amount of xenon gas. ) n o i t c e o j 10 − 47 P r r a e y t 0 2 ( T n N • A development of purity O N E X t m i i l y r e v o c s i d 10 − 48 o n i r u t e n , 3 monitor was reported. 1 0 2 d a r l l B i Bagnaschi 2017 10 − 49 • It is planned to start 10 1 10 2 10 3 detector commissioning WIMP mass [GeV/c 2 ] in 2019; construction is ongoing. 22
Appendix 23
Diving “Bell” to keep liquid level arXiv: 1107.2155 E. Aprile et al. 24
Energy resolution 25
Rn in XENON1T and XENONnT XENON1T ~10 µ Bq/kg Reduction 31%: QDrive pump à reduce by pump exchange 46%: Cryogenic pipes r: à reduce by extracting and e remove radon before it enter the TPC using dist. col. 19%: TPC+Inner vessel Cryogenic Porcupine Distillation à dilute by Rn-depleted LXe system 250 mm cryogenic pipe 100 mm column Add LXe purification pipe + cables Rn Rn screening and clean decay assembly is more important. QDrives Update the pie chart. TPC Getters → LXe Aim to have ~1 µ Bq/kg Purification system 26 Inner Vessel purification –
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