The XMASS 800kg Dark Matter Detector in Kamioka, Japan · The XMASS 800kg Dark Matter Detector in Kamioka, Japan Kai Martens Kavli-IPMU (WPI) The University of Tokyo for the XMASS

The XMASS 800kgDark Matter Detector

in Kamioka, JapanKai Martens

Kavli-IPMU (WPI)The University of Tokyo

for the XMASS collaboration

@ ICRC 2013, Rio de Janeiro

The XMASS collaboration:Kamioka Observatory, ICRR, Univ. of Tokyo ：

K. Abe, K. Hieda, K. Hiraide, Y. Kishimoto, K. Kobayashi, S. Moriyama, M. Nakahata, N. Oka, H. Ogawa, H. Sekiya, A. Shinozaki, Y. Suzuki, O. Takachio, A. Takeda, D. Umemoto, M. Yamashita, B. Yang Kavli IPMU, University of Tokyo ： J.Liu, K. MartensKobe University: K. Hosokawa, K. Miuchi, A. Murata, Y. Ohnishi, Y. TakeuchiTokai University: F. Kusaba, K. NishijimaGifu University ： S. TasakaYokohama National University ： K. Fujii, I. Murayama, S. NakamuraMiyagi University of Education ： Y. FukudaSTEL, Nagoya University ： Y. Itow, K. Masuda, H. Takiya , H. UchidaSejong University ： N. Y. Kim, Y.D. KimKRISS: Y.H. Kim, M.K. Lee, K. B. Lee, J.S. Lee

July 6, 2013 Kai Martens @ ICRC 2013 for XMASS 2

Outline

- experimental program

- current experiment: XMASS 800 kgdesign and calibration

- XMASS 800kg refurbishment

- next step: XMASS 1.5 ton

XMASS results were already presented here at ICRC 2013:session DM-EX01, presentation 131 last Tuesday...


The XMASS Experiment

Xe detector for weaklyinteracting MASSive particles

Xe -MASS detector Xe MASSive -detector

exploiting Xenon:

- high mass number → SI cross section- no long-lived radioactive isotope- good scintillation yield: ~ 46ph/keV- high density (liquid): 3g/cm3

- 48% odd isotopes (natural) → SD cross section- ββ candidate: 136Xe → 136Ba+2e+2.48MeV


The XMASS Experimental Program:

100kg reference:arXiv:0912.2405

the PAST:100kg prototype,

(3kg fiducial), 30cmproof of principle

the current incarnation:XMASS 800kg

(100kg fiducial), Ø 80cm

technologyadvantages:

- simple- scalable- self-shielding

24t, + ⊙

(10t fiducial)

Ø 2.5m

the next step:XMASS 1.55 ton total,

1 ton fiducial

future:the ultimate XMASS...

for XMASS resultssee: DM-EX01 131

(was Tuesday...)Y. Suzuki, hep-ph/0008296


The Kamioka Observatory:

KamLAND (Xe)

CANDLES

NEWAGEEGADS

Super-Kamiokande,(T2K)

XMASS

IPMULab

CLIO Legend:DM, , , GW

3km

to M

ozum

i

new: KAGRA

Tokyo

Nagoya

IPMU Lab:U, Th → HP-Ge ← few 100ppt

→ ICP-MS ← 1ppq*Kr → API-MS ← 1ppt*

* after concentration


Hall C in Kamioka: XMASS

Hall C: 15m,21m,15m (h,d,w)

water in tank:10m high

10m Ø

outer detector bigenough for final20 ton detector


XMASS from the Outside In:

outer detector (OD):72 x 20inch PMTs

Hamamatsu R3600

calibrationport

inner detector (ID):642 x 2 inch PMTs

Hamamatsu R10789-11LXe: 1100 kg

(total) 835 kg

(inside PMTs)

100 kg(fiducial)


Inner Detector Structure:2nd

LAYER

FILLER

LXe in detector:1100kg

in sensitive volume:835kg


Electronics:

new: FADCs

CAEN V17518 ch/board

bandwidth 500MHz,sampling rate 1GS/s

resolution 10bit1.2 μs window

so far: Super-Kamiokande ATMs

12 bit ADC/TDCintegration: -100ns – +300ns

1.2 μs window

both systems will run in parallel ← signal is split


XMASS Calibration System:“internal” γ calibration for XMASS:

- 57Co (122keV) ← anchor of energy scale

- 241Am (59.5keV), 109Cd (88keV), 55Fe (5.9keV)

“external” (hose)- 60Co, 137Cs- 252Cf neutrons (need FADC)

(different sources → slightly different shapes [materials...])


Low BG PMT Development:

Hamamatsu R10789: QE 28-39%+

XMASS photocathode coverage: 62.4%⇓

light yield: 14.7 PE/keV @ 122 keV

BG: biggest worry → PMTspecial development; incl. base:U-chain 0.70±0.28mBq/PMTTh-chain 1.5±0.31 mBq/PMT40K < 5.1 mBq/PMT60Co 2.9±0.16 mBq/PMT

… but:total BG larger than expectedyet comparable to other experiments,like CRESST, CDMS, or CoGeNT


What Did We Learn?surface contamination: β-decays...main culprits:- PMT aluminum seal: 210Pb, 238U chain- Cu surface: 210Pb (222Rn exposure...)


XMASS Refurbishmentcountermeasures:

- surface cleanup ← Cu electropolished: “rm -r U* Th*”

- remove Gore-Tex (presumed guilty until proven innocent … )

- cover PMT aluminum seal:- vapor deposition of Al on side of window- Cu ring around aluminum seal- electropolished Cu cover above Cu rings


Radon & Dust: Defense in Depth(pictures from 2010 detector assembly:)

this time:

hall C → now clean room (class 1000)

→ three levels of clean roomto tent in water tank

→ much improved clean roomconditions at assembly site

also improved: - radon free air availability and flow- PMT holder will be kept in special encasing during

assembly→ expect better than one order of magnitude reduction in background !!!


On the Way to XMASS 2: XMASS 1.5- still a DM detector- inner Ø: 1.5 m- contains 5 tons of LXe- fiducial mass 1 ton~ 1800 PMTs (or move to 3 inch ?)

lessons from XMASS 800kg:new PMTs!

w/dome-shaped photocathode← see nearby surface !!!

want to startin 2014 !!


New PMT for XMASS 1.5actively being developed w/Hamamatsu:

dome shaped photocathodeto detect light entering from the side:i.e. from the surrounding surfaces...

→ effectiveness verified by MC

(photos show prototype; no final design yet)


Conclusions- there is a well developed and active Dark Matter program at Kamioka

- our self-shielding, single phase LXe detector technology is:← producing results← readily scalable← delivering high light yield → low threshold

- initial contamination problems are understood and being addressed:← the fundamental technology is debugged and proven !

- XMASS 800kg data taking will resume in September 2013:← stay tuned !!

- XMASS 1.5 will start in 2014:← look forward !!!


Backup


57Co Calibration: reconstruction:data MC

@ center:data vs. MC

W (59.3 keV)

57C

o (1

22 k

eV)

57C

o (1

36 k

eV)

center position setsenergy scale:

→ 14.7 p.e./keVee

resolution 4% rms


Xe Distillation: (85)Kr Removal

K.Abe et al, Astroparticle Physics

31(2009), p290

capacity of XMASS Xe distillation system:6kg/h; did 1 ton in ~ 1 week → (3.3±1.1)ppt

otherwise:extensive materials validationbefore construction:

IPMU Lab:U, Th → HP-Ge ← few 100ppt

→ ICP-MS ← 1ppq*Kr → API-MS ← 1ppt** after concentration

hall C distillation system:(used before filling detector)

experience:detector stable w/o:- routine getter operation- active Rn removal


Decay Chains:

from: http://radiokimia.blogspot.com.br/2011/04/u-235-u-238-and-th-232-decays-series.html


Background Comparisons:

XMASS 800kg full volume

Documents

The XMASS 800kg Dark Matter Detector in Kamioka, Japan · The XMASS 800kg Dark Matter Detector in Kamioka, Japan Kai Martens Kavli-IPMU (WPI) The University of Tokyo for the XMASS