XENON NT EXPERIMENT
Columbia University
JSPS Postdoctoral research fellow
Masatoshi Kobayashi

TABLE OF CONTENT➤ Introduction: XENON experiment➤ XENONnT experiment: What’s new from XENON1T?
➤ XENONnT TPC➤ External systems (Purification, Rn distillation, nVeto, Xe Storage)➤ Expected performance➤ WIMPs sensitivity➤ BG➤ Current status of construction

INTRODUCTIONINTRODUCTION: THE XENON PROJECTThe XENON Collaboration~ 170 scientists H 26 institutions H 11 countries

INTRODUCTION: THE XENON PROJECTTechnical meeting @May 2020

The XENON Project + DARWININTRODUCTION: THE XENON PROJECT (AND DARWIN)INTRODUCTION: THE XENON PROJECT➤ Located at Laboratori Nazionali delGran Sasso (LNGS), Italy➤ XENON1T water tank + building➤ Top: Cryogenics/Purification➤ Middle: DAQ/Slow Control➤ Bottom: Storage/Distillation➤ Being upgraded for XENONnTXENON NT EXPERIMENT:
WHAT’S NEW FROM XENON1T?

T

XENONnTXENON NT EXPERIMENT: XENONNT TPC➤ XENONnT TPC➤ Diameter=1.3m, Height=1.5m➤ LXe mass:➤ Full: 8.2 ton~1.5m➤ Active: 5.9ton➤ Fiducial: 4 ton➤ 3 times larger than XENON1T~1.3m➤ Top/bottom PMTs : 253/241

XENON NT EXPERIMENT: XENONNT TPC➤ XENONnT TPC➤ Diameter=1.3m, Height=1.5m➤ LXe mass:➤ Full: 8.2 ton➤ Active: 5.9ton➤ Fiducial: 4 ton➤ 3 times larger than XENON1T➤ Top/bottom PMTs : 253/241

XENON NT EXPERIMENT: XENONNT TPC➤ Low energy ER Background: 1/6 fromXENON1T➤ Reduction of Rn222 : 1uBq/kg➤ Expected event rate
➤ ~0.035 event/day/keV/ton➤ ~0.2 in XENON1TXENON NT EXPERIMENT: NEW EXTERNAL SYSTEM

Purification

Rn distillation

Neutron veto

Xenon Storage

XENON NT EXPERIMENT: NEW EXTERNAL SYSTEM

Purification

Rn distillation

Neutron veto

Xenon Storage

XENON NT EXPERIMENT: NEW EXTERNAL SYSTEM
Two-phase Xe Time Projection
Chamberas
WIMP
detector
Purification➤ Signal
generation
LXe:
Particleinteractions inin LXelead to primary•

scintillation (S1) and the release of ionization➤ S1:
electrons
Scintillation photons
Ionizationelectronselectrons
drift towards the liquid➤ •S2:
Ionization

gas interface under the uniform electric field,
get extracted and accelerate in the GXe,
➤ Impurities in Xe (ex: H2O, O2)
producing secondary scintillation (S2), whose
magnitude is proportional to the number of➤ H2O:
Reduceextracted
electronsattenuation length

Neutron veto➤ •O2:
Electronlifetimeelectron
is used to characterize
the S2Absorb
and reduce
absorption of the ionization electrons driftingin LXe by electronegative impurities (mainlyoxygen):Qf = Qietd− τetd⇒ τe =−ln(Q /Q )

XENON NT EXPERIMENT: NEW
WHAT’S
EXTERNAL
NEW FROMSYSTEMXENON1T?
Purification

GXe lineLXe line
5LPM

GXeCryostat➤ Xenon1T purification system

GXepump➤ Evaporate LXe and purify withGetter

LXe
50SLPMHeat
Exchanger
Evaporation
Condensation

Zr-Fe-V (+HRU) getter➤ Upgrade: Magnetic GXe pump

Neutron veto

➤ Low Rn emanation➤ Rn level reduced ~45%

with test in 1T➤ Speed: ~100 SLPMXENON NT EXPERIMENT: NEW
WHAT’S
EXTERNAL
NEW FROMSYSTEMXENON1T?
Purification

GXe lineLXe line

GXeCryostat➤ Xenon1T purification system

GXepump➤ Evaporate LXe and purify withGetter

LXeHeatExchanger
Evaporation
Condensation

Zr-Fe-V (+HRU) getter➤ Upgrade: Magnetic GXe pump

Neutron veto

➤ Low Rn emanation➤ Rn level reduced ~45%

with test in 1T➤ Speed: ~100 SLPMXENON NT EXPERIMENT: NEW
WHAT’S
EXTERNAL
NEW FROMSYSTEMXENON1T?
Purification

GXe lineLXe line➤ Xenon1T purification system

GXepump

GXe
Cryostat➤ Evaporate LXe and purify withGetter

LXe

Zr-Fe-V (+HRU) getter➤ Upgrade: Magnetic GXe pump

100SLPM

Heat
Exchanger
Evaporation
Condensation

Neutron veto

➤ Speed: ~100 SLPM
➤ Low Rn emanation➤ Rn level reduced ~45%

with test in 1T

XENON NT EXPERIMENT: NEW
WHAT’S
EXTERNAL
NEW FROMSYSTEMXENON1T?
Purification

GXe lineLXe line

GXe
Cryostat

GXepump

LXepump➤ Speed: ~100 SLPM

GetterLXe
O2Filter➤ Xenon1T purification system➤ Not enough for XENONnT…
➤ New system for XENONnTHeat
Exchanger
Evaporation
Condensation➤ LXe purification circuit

Neutron veto➤ ~3 LPM= 1500 SLPMXENON NT EXPERIMENT: NEW
WHAT’S
EXTERNAL
NEW FROMSYSTEMXENON1T?
Purification➤ Direct liquid circulation➤ Barber-Nicols cryogenic pump
➤ Besed on LAr technology(ICARUS experiment)➤ Oxigen removal➤ Remove O2 by chemical

reaction of Pure-Cu➤ Purity measurement by purity

monitorXENON NT EXPERIMENT: NEW
WHAT’S
EXTERNAL
NEW FROMSYSTEMXENON1T?
Purification➤ Direct liquid circulation➤ Barber-Nicols cryogenic pump
➤ Besed on LAr technology(ICARUS experiment)➤ Oxigen removal➤ Remove O2 by chemical

reaction of Pure-Cu➤ Purity measurement by purity

monitorXENON NT EXPERIMENT: NEW
WHAT’S
EXTERNAL
NEW FROMSYSTEMXENON1T?

Purification

Rn distillation

Neutron veto

Xenon Storage

XENON NT EXPERIMENT: NEW
WHAT’S
EXTERNAL
NEW FROMSYSTEMXENON1T?
Rn distillation➤ “Inverse distillation” of Kr/Ar distillation

Rn-depletedoﬀ gas
Inlet gas

➤ Rn atom accumulates into LXe morethan GXe➤ Kr/Ar distillation: dirty oﬀ-gas➤ Rn distillation: pure oﬀ-gas➤ Rn atoms are kept in the column anddecays➤ Already tested in XENON100,XENON1TXENON NT EXPERIMENT: NEW
WHAT’S
EXTERNAL
NEW FROMSYSTEMXENON1T?
Rn distillation

222Rn➤ Take Xe partially from LXePUR system, andGXePumps

back Rn-free Xe
MaincolumnDistillation➤ One of Rn source in Xenon1T:➤ Cryogenic/purification system214
 Reduce Rn ( Pb)➤ Active circulation also with external systems

from pipes, cables &send
Rn-freeXebacktoTPC
cryogenic system➤ Suck Rn-rich Xe from external pipes, then

➤ Expected speed: ~200 SLPMXENON NT EXPERIMENT: NEW
WHAT’S
EXTERNAL
NEW FROMSYSTEMXENON1T?

Purification

Rn distillation

Neutron veto

Xenon Storage

XENON NT EXPERIMENT: NEW
WHAT’S
EXTERNAL
NEW FROMSYSTEMXENON1T?
Reﬂector (Tyvek/Gore-Tex)

Neutron veto
➤ Neutron Veto system➤ Gd-Water Cherenkov detector➤ Neutrons from cryostat will becaptured by Gd and produce 8MeVgamma➤ Entire Cryostat will be surroundedby the ePTFE structure➤ Collect photons as much aspossible

XENON NT EXPERIMENT: NEW
WHAT’S
EXTERNAL
NEW FROMSYSTEMXENON1T?
Neutron veto
➤ Tagging eﬃciency: ~80-90% basedon simulation➤At 0.5% Gd2(S04)3・8H20➤ Upgrade for Gd-water purification➤ Based on EGADS technology➤ Purity/reflectivity measurement

systems are installedXENON NT EXPERIMENT: NEW
WHAT’S
EXTERNAL
NEW FROMSYSTEMXENON1T?
Neutron veto
➤ Tagging eﬃciency: ~80-90% basedon simulation➤At 0.5% Gd2(S04)3・8H20➤ Upgrade for Gd-water purification➤ Based on EGADS technology➤ Purity/reflectivity measurement

systems are installedXENON NT EXPERIMENT: NEW
WHAT’S
EXTERNAL
NEW FROMSYSTEMXENON1T?

Purification

Rn distillation

Neutron veto

Xenon Storage

ReUse XENON1T ReStoX

ND STORAGE‣ Vacuum-insulated storage system withX

Additional ReStoX2‣ Foam-insulated 9storage system withXENONAdditional
NT EXPERIMENT:
WHAT’SNEWEXTERNALNEW FROMSYSTEMXENON1T?
ReStoX2

capacity of 7.6 t of Xe (gaseous, liquid or

capacity of 10 t of Xe (gaseous,solid)
liquid or solid)ystem with
‣ Foam-insulated storage system with
‣ LN2 based cooling system (35 kg / d)
‣ Very fast recovery with Xe freezing
eous, liquid or
capacity of 10 t of Xe (gaseous,(1t / hour)‣ Fast recovery
in caseof accident/liquidor solid)

Xenon Storage

maintenance (~50kg/h)‣ Maximum pressure: 71.5 bar
35 kg / d)
‣ Very fast recovery with Xe freezing‣ Maximum pressure:73 bar‣ LN2 consumption➤(1t / hour)
RestoX2ident/
RestoX1
for recovery: ~ 8000 kg‣ Fully controlled by SCS‣ Maximum pressure: 71.5 bar‣ Construction completed‣ LN2 consumption‣ Already delivered to LNGS,➤for recovery: ~ 8000 kg
commissioning and tests
5.5m‣ Construction completed
are ongoing!

Total amount of Xenon for thedetector:➤ XENONnT: ~8 ton‣ Already delivered to LNGS,
commissioningand tests
2.1m

XENON1T: ~3 ton➤ Upgrade of Xenon Strage +5.5m

are ongoing!

Emergency recuperation1m

1.45m➤ ReStoX1:GXe + LXe, 7.5ton

1.45m➤ ReStoX2: GXe + SXe, 9ton

XENON NT EXPERIMENT: NEW
WHAT’S
EXTERNAL
NEW FROMSYSTEMXENON1T?
Xenon Storage

GXe line➤ RSX1: upgrade from 1T➤ Quick LXe recuperation with new line
➤ Common liquid line with purification

Cryostat➤ RSX2: new system for nT➤ Quick GXe recuperation by freezing Xegas

LXe line

RSX2
RSX1

➤ Keep all Xe gas in room temperature➤ All GXe lines are connected to GXePUR too

XENON NT EXPERIMENT: NEW
WHAT’S
EXTERNAL
NEW FROMSYSTEMXENON1T?
GXe line

GXePUR

Xenon Storage➤ RSX1: upgrade from 1T➤ Quick LXe recuperation with new line
➤ Common liquid line with purification

Cryostat➤ RSX2: new system for nT➤ Quick GXe recuperation by freezing Xegas

LXe line

RSX2
RSX1

➤ Keep all Xe gas in room temperature➤ All GXe lines are connected to GXePUR too

EXPECTED SENSITIVITY(BASED ON ARXIV:2007.08796)

BACKGROUND:ERSource

ROI for WIMPs

ER background
Detector radioactivity
222Rn85
Kr136
Xe124
Xe
Solar neutrinos
Total

Rate [(t y)−1 ]25 ± 366 ± 713 ± 1
16 ± 24±1
34 ± 1
158 ± 8NR background−2Neutrons(4.1 ± 2.1) × 10
➤ Largest background: from Rn222 and its−3 daughter
CEνNS (Solar ν)(6.3 ± 0.3) × 10−2
CEνNS(Atm+DSN)(5.4±1.1)
×10➤ Here, target value is 1 uBq/kg
Total(1.0 ± 0.2) × 10−1
➤ Detector radioactivity: single Compton scattering

Table 3: Estimated background event rates in the 4 t fiducial volume of XENONnTenergy of the recoil event.➤Theenergy ROI
which theandevent
rates are integrated isGammas
frominCryostat
PMTs
ERs, and (4, 50) keV for NRs. We assume an activity concentration of 1 µBq/kg of 222 R(mol/mol) nat Kr/Xe. The background contributions from Xe isotopes are determinedBACKGROUND:NR

Detector radioactivity
222
Rn85
Kr136
Xe124
Xe
Solar neutrinos
SourceTotal

25 ± 366 ± 713 ± 1
16 ± 24±1
34 ± 1
Rate
158[(t±y)8−1 ]ER backgroundNRbackground
Detector radioactivity (4.1 ± 25
Neutrons2.1)±×3 10−2
222
Rn (Solar ν)
CEνNS(6.3 ± 660.3)±×7 10−3
85−2Kr13±1
CEνNS(Atm+DSN)(5.4±1.1)
×10
ROI for WIMPs
136
Xe
Total
(1.0 ± 160.2)±×2 10−1
124
Xe
4±1
Solar event
neutrinos
34 ±volume
1
Table 3: Estimated backgroundrates in the 4 t fiducialof XENONnT
Total
158 ±rates
8 are integrated isenergy of the recoil event. Theenergy ROI in which the event➤ Radiogenic neutron and high energy
ERs, and (4, 50) keV for NRs.NRWe backgroundassume an activity concentration of 1 µBq/kg of 222nat(mol/mol)
Kr/Xe. Theneutrino
backgroundcontributions
fromXeisotopes
determinewouldhave
similarlevelof
BG−2areNeutrons 136(4.1 ± 2.1) × 10
124
8.9% and 0.095% natural abundancesofXeandXe,respectively.
−3
CEνNS (Solar ν)(6.3 ± 0.3) × 10
➤ nVeto eﬃciency: ~87%

CEνNS (Atm+DSN)
Total(5.4 ± 1.1) × 10−2
(1.0 ± 0.2) × 10−1

CEνNS neutrinos ➤ Main neutron source: Cryostat, PMTs,

Table 3: Estimated backgroundevent rates in the 4 t fiducial volume of XENONnTPTFE
Neutrino interactions from solar, atmospheric and diffuse supernova (DSN) neutrinos coenergy of the recoil event. The energy ROI in which the event rates are integrated
is8NR background through CEνNS. Solar neutrino backgrounds (predominantly B and hep
222
ERs, and (4, 50) keV for NRs. We assume an activity concentrationof
1µBq/kgof
2limit the sensitivity
toWIMPswithmassesofafew
GeV/c. In contrast, the NR snat

EXPECTED SENSITIVITY (SI WIMP)➤ Expectedsensitivity
underBGs in previous
in 20 typower in the search for spinFigure
6: Projectionsof theXENONnT
sensitivity pages
and discovery
independent WIMP-nucleon couplings. (Left) Median 90% CL exclusion limit (black solid line) for➤ At 50GeV, even first few month of data could beat Xenon1T best limit by factor 3-4
a 20 t y exposure, with the 1σ (green) and 2σ (yellow) bands. The current strongest exclusion limit,
obtained with XENON1T [3], is shown in blue. The gray dashed-dotted line represents the discoverySENSITIVITY VS TRITIUM➤ On the other hand, recent study of

XENON1T shows excess at low energy ER➤ If the excess is due to the tritium: 6x10-25mol/mol (middle dashed line)➤ If we have more than 7x10-25 mol/mol, it willbe the same with the summation of all otherER backgrounds➤ Because of the spectrum shape, lighter theWIMPs mass is, smaller the eﬀect is.

3

SENSITIVITY VS TRITIUM➤ On the other hand, recent study of

XENON1T shows excess at low energy ER➤ If the excess is due to the tritium: 6x10-25mol/mol (middle dashed line)➤ If we have more than 7x10-25 mol/mol, it willbe the same with the summation of all otherER backgrounds➤ Because of the spectrum shape, lighter theWIMPs mass is, smaller the eﬀect is.

a in the XENONnT 4 t fiducial volume. The H
3

EXPECTED SENSITIVITY: TRITIUM VS ER SIGNAL (AXION) ?
➤ So far, the sensitivity for WIMPs has been

discussed…
➤ How about the sensitivity for Low energy

excess?

➤ Axion spectrum is continuous, but also havesome peak-like shape➤ Tritium: smooth beta-decay, Q=18keV➤ Distinguish tritium and axion based on thediﬀerence of spectrum?

EXPECTED SENSITIVITY: TRITIUM VS ER SIGNAL (AXION) ?
➤ Discrimination power betweenaxion and tritium➤ Note: BGs are based on 1T

best fit➤ If Rn BG level is enough low,axion/tritium could be
distinguished with few month ofdata➤ Ex. ~4 sigma with 1-3 uBq/kg

CURRENT STATUS

STATUS OF XENONNT: TPC CONSTRUCTION➤ TPC construction: Feb. 2020
➤ Constructed in the CR above ground, then brought to UG

STATUS OF XENONNT: TPC CONSTRUCTION➤ TPC construction: Feb. 2020
➤ Constructed in the CR above ground, then brought to UG

1T18)STATUS OF XENONNT: TPC CONSTRUCTION➤ TPC construction: Feb. 2020
➤ MountedXENONnTto the cryostat, and the closed on March 2020(2019-20xx)

STATUS OF XENONNT: TPC COMMISSIONING➤ Because of the corona virus, the activity at LNGS was limited…
➤ However: Detector commissioning in vacuum➤ PMT, LED, DAQ, Data analysis tool, etc etc…
➤ After the lock down: commissioning with GXe➤ “First S1 light” in GXe have been observed alreadyFirst scintillation pulses in GXe!

wwTwitter: httpsFacebook: https://wSTATUS OF XENONNT: NVETO CONSTRUCTION➤ Also nVeto construction has already started:

STATUS OF XENONNT: NVETO CONSTRUCTION➤ Also nVeto construction has already started:

STATUS OF XENONNT: CRYOSTAT FILLING➤ I myself also entered to Italy on July:➤ Cryogenics upgrade➤ Rn column installation➤ GXe purification➤ Cryostat cool down
➤ Recent news: Cryostat LXe fillingstarted!
➤ Also a lot of other works are ongoing!

LNGS Cryo-team at the moment of LXe filling