the xmass experiment to search for dark matter at the ......caen v1751 8 ch/board bandwidth 500mhz,...
TRANSCRIPT
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The XMASS Experimentto search for Dark Matter
at the Kamioka Observatory
Status and Previous Results
Kai Martens
Kavli IPMUThe University of Tokyo
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November 27, 2013 Kai Martens, Kavli IPMU, @ Osaka City University 2
Outline
- Kavli IPMU: a word about my institute
- Dark Matter: setting the stage
- Kamioka Observatory: the preeminent underground sciencelaboratory in Japan
- XMASS Experiment: - design
- results from first commissioning phase
- refurbishing
- the next step in the program
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November 27, 2013 Kai Martens, Kavli IPMU, @ Osaka City University 3
Kavli IPMU
one of the 5 original WPI centers:- founded Oct. 1, 2007- first institute in Todias Jan. 11, 2011- first Kavli institute in Japan May 10, 2012
best evaluations among WPI centers5 year “extension” to be decided soon...
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November 27, 2013 Kai Martens, Kavli IPMU, @ Osaka City University 4
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
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November 27, 2013 Kai Martens, Kavli IPMU, @ Osaka City University 5
The XMASS CollaborationKamioka Observatory, ICRR, University of Tokyo:
Y. Suzuki, M. Nakahata, S. Moriyama, M. Yamashita, Y. Kishimoto,
A. Takeda, K. Abe, H. Sekiya, H. Ogawa, K. Kobayashi, K. Hiraide, B. Yang,
K. Ichimura, A. Shinozaki, K. Hieda, O. Takachio, D. Umemoto, N. Oka,
K. Nakagawa, M.Kobayashi
IPMU, University of Tokyo: K. Martens, J.Liu
Kobe University: Y. Takeuchi, K. Miuchi, K. Hosokawa, A. Murata, Y.Ohnishi
M. Kobayashi
Tokai University: K. Nishijima, F. Kusaba
Gifu University: S. Tasaka
Yokohama National University: S. Nakamura, I. Murayama, K. Fujii
Miyagi University of Education: Y. Fukuda
STEL, Nagoya University: Y. Itow, K. Masuda, H. Uchida, H. Takiya
Sejong University: Y.D. Kim, N.Y. Kim
KRISS: Y.H. Kim, M.K. Lee, K.B. Lee, J.S. Lee
45 collaborators, 10 institutions, 2 countries
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November 27, 2013 Kai Martens, Kavli IPMU, @ Osaka City University 6
Early Observations: Oort & Zwicky 1932: Jan Oort (Leiden, Netherlands):
“measures” matter in galactic disk near sun from motion of nearby stars: 1M
⊙/375ly3 > 2m
stars
→ dark matter
1933: Fritz Zwicky (Caltech, USA):
virial theorem: ΣT = ½ ΣU→ galaxies in Coma cluster too fast for cluster's gravitational potential
→ dark matter
Vera Rubin @ Carnegie Institutionof Washington:
rotation curves of galaxies1975 AAS meeting
1980 paper
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November 27, 2013 Kai Martens, Kavli IPMU, @ Osaka City University 7
New Scientist (2005/03/19): Michael Brooks: 13 things that do not make sense: Maybe we can't work out what dark matter is because it doesn't actually exist. That's certainly the way Rubin would like it to turn out. "If I could have my pick, I would like to learn that Newton's laws must be modified in order to correctly describe gravitational interactions at large distances," she says. "That's more appealing than a universe filled with a new kind of sub-nuclear particle."
@ Carnegie Institutionof Washington:
1975 AAS meeting 1980 paperA: expected curve
given luminous matterB: observed curve...
http://apod.nasa.gov/ apod/ap110219.html:inner part of NGC 2841 by HST
measured60 galaxies
viagas clouds
(H, He)[not stars!]
vf
Galactic Rotation Curves: Vera Rubin
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November 27, 2013 Kai Martens, Kavli IPMU, @ Osaka City University 8
Dark Matter: It's out there …
http://apod.nasa.gov/apod/ap060824.html
http://cosmicweb.uchicago.edu/filaments.html
blue: DM, red: hot gas
≈
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November 27, 2013 Kai Martens, Kavli IPMU, @ Osaka City University 9
So What Are We Looking For?
- gravitating: the only thing we know for sure...
- cold: → massive ← if particle (cold DM...)
- collisionless: → no E/M interaction→ no strong interactionat most: weakly interacting ???
(Rubin as in: Vera Rubin)
New Scientist (2005/03/19): Michael Brooks: 13 things that do not make sense: Maybe we can't work out what dark matter is because it doesn't actually exist. That's certainly the way Rubin would like it to turn out. "If I could have my pick, I would like to learn that Newton's laws must be modified in order to correctly describe gravitational interactions at large distances," she says. "That's more appealing than a universe filled with a new kind of sub-nuclear particle."
favorites are: neutralino, axion, Kaluza-Klein, gravitino
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November 27, 2013 Kai Martens, Kavli IPMU, @ Osaka City University 10
Dark Matter and the WIMP Miracle
WIMP denomination → weak interaction ...
WIMP decoupling after BB:
velocity averaged annihilation cross-section for GeV-TeV mass WIMPs:
<σv> = 3×10-26cm3/s → correct DM density
TeV ~ SUSY partners ???
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November 27, 2013 Kai Martens, Kavli IPMU, @ Osaka City University 11
WIMP Dark Matter Searches:Direct Detection
from proceedings Tev06:Search for WIMPs with CDMS and XENON
two types of interaction:- spin dependent (odd isotopes), smaller cross section- spin independent; σ ~ A2 (coherent: whole nucleus)
important for verification:different target materials
→ consistency!
CDM → massive → nuclear recoil (NR) 50keV
NR → ~10keV
ee
calibration sources are γ-sources...(ee)
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November 27, 2013 Kai Martens, Kavli IPMU, @ Osaka City University 12
The Current Situation: (WIMP hypothesis:)
compatible:- spectra:
CoGeNT/CRESST-II- modulations:
DAMA/CoGeNT
tension:- Xe vs. all of the above- modulation amplitude(halo assumptions...)
two regions of experimental focus:- low threshold...- low background...
Fig. 5 of 1310.8214:LUX 1st results (90% CL)
Xenon100 225d, 100dCDMS II, ZEPLIN-III, Edelweiss II
allowed regions:CDMS II Si (95%)
DAMA/LIBRACRESST !!
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November 27, 2013 Kai Martens, Kavli IPMU, @ Osaka City University 13
The XMASS ExperimentXe detector for weakly
interacting MASSive particlesXe -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
Ultimately: 10t fiducial volume multi-purpose detector:- neutrino mass: ββ- Dark Matter: WIMP limited by:- solar neutrinos: pp, 7Be
(the water tank in Hall C is designed to hold this...)
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November 27, 2013 Kai Martens, Kavli IPMU, @ Osaka City University 14
XMASS Progression:
100kg reference:arXiv:0912.2405
the PAST:100kg prototype,
(3kg fiducial), 30cmproof of principle
the current incarnation:Phase I
835kg WIMP detector(100kg fiducial), 80cm Ø
detector technologyadvantages:
- simple- scalable- self-shielding
ultimately: 24t (10t fid.) 2.5m Ø
24t, + ⊙
(10t fiducial)2.5m
the (far) future:
the next step:5 ton total, > 1.5ton fiducial
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November 27, 2013 Kai Martens, Kavli IPMU, @ Osaka City University 15
XMASS Physics:
Phase I:100/835 kg
main purpose:DM direct detectionχ + Xe → χ + Xe
Phase II:10/25 t
multi purpose:DM direct detection:χ + Xe → χ + Xe
pp and 7Be solar neutrinos:ν + e– → ν + e–
neutrinoless double-β decay:136Xe → 136Ba + 2e–
current proposal:XMASS 1.5
to compete in the next roundof DM direct detection: ~1t hep/ph 0008296
Y. Suzuki
expected“singal”
rates [dru]:
low background speak:
dru(differential rate unit):
events / day / kg / keV
2ν2e– (2.38x1021y)
pp7Be10–6
10–4
χ m=50GeV
χ m=100GeV
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November 27, 2013 Kai Martens, Kavli IPMU, @ Osaka City University 16
Background Requirements:
WIMPs:
10-4 dru → cross sections down to a few times 10-45 cm2
solar neutrinos:
better than 10-5 druexpected rate in 10t: 14/d for pp + 6/d for 7Be
→ important considerations:- go underground (shielding against cosmogenic activation)- carefully select and monitor your materials for radio isotopes- shield your detector (against ambient radiation: 222Rn, n, γ)
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November 27, 2013 Kai Martens, Kavli IPMU, @ Osaka City University 17
Shielding Against Ambient Radiation
fast Neutron MC:
Xe
Watertank
fast neutrons:water tank
11m high (10m water)10m Ø
active: -veto
also
:h
all l
inin
g R
n r
etar
din
gR
n-”
po
or”
ou
tsid
e ai
r su
pp
ly
gamma radiation:xenon →
self-shielding:
inner pink circle: fiducial volume
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November 27, 2013 Kai Martens, Kavli IPMU, @ Osaka City University 18
Hall C in Kamioka: XMASS
Hall C: 15m,21m,15m (h,d,w)
water in tank:10m high
10m Ø
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November 27, 2013 Kai Martens, Kavli IPMU, @ Osaka City University 19
XMASS from the Outside In:
Outer Detector (OD):72 x 20inch PMTs (=SK)
calibrationport
Inner Detector(ID):642 PMTs
1100 kg LXe(total)
835 kg(inside PMTs)
100 kg(fiducial)
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November 27, 2013 Kai Martens, Kavli IPMU, @ Osaka City University 20
Inner Detector Structure:2nd
LAYER
FILLER
LXe in detector:1100kg
in sensitive volume:835kg
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November 27, 2013 Kai Martens, Kavli IPMU, @ Osaka City University 21
Building the Inner Detector 1:
photocathodecoverage:
62.4%
xenon insidethe photocathodes:
835 kg
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November 27, 2013 Kai Martens, Kavli IPMU, @ Osaka City University 22
Building the Inner Detector 2:
Feb
2010
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November 27, 2013 Kai Martens, Kavli IPMU, @ Osaka City University 23
Low BG PMT Development:
630 hexagonal + 12 round) PMTs:
Hamamatsu R10789: QE 28-39%+
XMASS photocathode coverage: 62.4%
BG: biggest worry → PMT
great development:
U < 1.0Th< 0.94K < 9.68Co = 4.47±0.34
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November 27, 2013 Kai Martens, Kavli IPMU, @ Osaka City University 24
Electronics:
new: FADCs
CAEN V17518 ch/board
bandwidth 500MHz,sampling rate 1GS/s
resolution 10bit1.2 μs window
Super-Kamiokande ATM:
12 bit ADC/TDCintegration: -100ns – +300ns
1.2 μs window
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November 27, 2013 Kai Martens, Kavli IPMU, @ Osaka City University 25
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
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November 27, 2013 Kai Martens, Kavli IPMU, @ Osaka City University 26
XMASS Calibration System:
sourceexchange
“internal” γ calibration for XMASS:- 57Co (122keV) ← main anchor of energy scale
- 241Am (59.5keV), 109Cd (88keV), 55Fe (5.9keV)
“external” (hose)- 60Co, 137Cs- 252Cf neutron calibration (needs FADC)
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November 27, 2013 Kai Martens, Kavli IPMU, @ Osaka City University 27
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:
→ 13.8 p.e./keVee
energy resolution: 4% rms
position resolution (rms):center: 1.4 cm±20cm: 1.0 cm
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November 27, 2013 Kai Martens, Kavli IPMU, @ Osaka City University 28
Energy Scale Evolution
photoelectron yield is continually improvingeven after we stopped forcing circulation through hot getters!
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November 27, 2013 Kai Martens, Kavli IPMU, @ Osaka City University 29
Detector Stability
det
ect
or
stu
dy
det
ecto
rst
ud
y
tracking intrinsic background signals with our 57Co energy scale:
ratio
w/a
vera
ge →
46 keV 0.47%variablity: 1.1MeV 0.60%
1.3 MeV 0.36%
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November 27, 2013 Kai Martens, Kavli IPMU, @ Osaka City University 30
Extrapolating the Energy Scale
XMASSanalysisthreshold
nuclear recoil scintillation efficiency Leff
follows Xenon100 (arXiv 1104.2549):
57Co
55Fe
109Cd
241Am
above linear fit is used to interpolatekeV
ee energies between calibration
points (from internal gamma sources)and extrapolate to lower energies
dominantsystematic..
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November 27, 2013 Kai Martens, Kavli IPMU, @ Osaka City University 31
XMASS Unexpected BG: The Culprit:
the culprit:Al seal for PMT window:
238U and 210Pb found in raw material(not in secular equilibrium)
unexpected BG traced tosurface between PMTs:
β may deposit most energyinside the material
→ low energy signal...
first suspect:Gore-Tex (light barrier) under PMT rim:
may contain up to 6% modern carbonbut: no signal when measured in XMASS
(no longer needed after refurbishment)
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November 27, 2013 Kai Martens, Kavli IPMU, @ Osaka City University 32
Main BG Source: PMT Al Seal...shape assumed inoriginal MC production:
(full volume)
shape derived fromPMT inspection:
(full volume)
Surface 210PbPMT Al 235U-231PaPMT Al 210PbPMT Al 232ThPMT Al 238U-230ThPMT gammaDots: XMASS data
E > 5 keVee
:
BG understood!
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November 27, 2013 Kai Martens, Kavli IPMU, @ Osaka City University 33
The Good News: BG (Low), LY high(still optimizing: reduce leakage of surface events into FV)
but:
graph (- XMASS...)taken from:
E. Aprile(Princton 2010)
high light yield (LY) → low threshold → go for light WIMPs
(heavy WIMPs → large A → large cross section → to come)
XMASS full volume !!!
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November 27, 2013 Kai Martens, Kavli IPMU, @ Osaka City University 34
Light WIMPs:Full Volume, Low Threshold
playing to our strength:
full volume = 835kg4 hit threshold = 6.75 days(now standard after refurbishment)
backgrounds to be considered: cuts applied:
- no OD activity → ID trigger only- no afterpulse activity → timing RMS < 100ns- Cherenkov (40K in photocathode) → q(20ns)/q(total) < 0.6- ringing, radioactivity → ± Δt > 10ms
systematics to account for:L
eff, energy resolution & scale, trigger efficiency, cuts
our limit:maximally allowed
cross section:MC prediction < data
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November 27, 2013 Kai Martens, Kavli IPMU, @ Osaka City University 35
Cherenkov CutCherenkov light emission in PMT glass (40K, …)
Cherenkov photons emitted “immediately”:→ PMT timing resolution (~3.5ns)
scintillation events:→ time constant τ ~ 25ns (low energy γ and nucl. recoil)
cut parameter:
charge(first 20ns) charge(total)
keep < 0.6
efficiency varies with p.e. range: 40% – 70%
data MC
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November 27, 2013 Kai Martens, Kavli IPMU, @ Osaka City University 36
Trigger Threshold & Data Reduction
70%
30%
signal efficiency(MC)
w/fit
(for low threshold data used inlow-mass WIMP and axion searches)
LED data
6.7d low thresholddata
signal efficiency after all cuts →
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November 27, 2013 Kai Martens, Kavli IPMU, @ Osaka City University 37
XMASS Low Mass WIMP Result:
systematic contributions:(in order of declining importance)
- Leff
uncertainty *(solely responsible for red shaded)
- energy resolution
- trigger efficiency
- energy scale
- Cherenkov cut(all fit into thick red line...)
* following arXiv 1203.1589 (Xe100)
Phys. Lett. B719 (2013) 78; arXiv 1211.5404
limit by:SG ≤ BG
data
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November 27, 2013 Kai Martens, Kavli IPMU, @ Osaka City University 38
Solar Axions through Axio-Electric:production in the sun:- g
aN: nuclear de-exitation (57Fe, line @ 14.4keV)
- gaee
: Bremsstrahlung, Compton
- gaγγ
: Primakoff effect
XMASSsolar axion limit:g
aee< 4.5x10-11in
dire
ct b
ound
fro
m s
olar
ν fl
ux detectionin XMASS: axio-electric
samestraightforward
limitevaluation
Phys. Lett. B724 (2013) 46arXiv: 1212.6153
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November 27, 2013 Kai Martens, Kavli IPMU, @ Osaka City University 39
Annual Modulation Analysis
136.1 days (2010/12-2012/5)835kg → 0.31 tythreshold (analysis): 1 keV
ee
fit functiont0, ω fixed!
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November 27, 2013 Kai Martens, Kavli IPMU, @ Osaka City University 40
Annual Modulation ResultStandard HaloModel
(from: 1209.3339)
difference:summer-winter
solid: summerdashed: winter
JPS fall 2013:XMASS 90% CL
CDMS II 2009Xenon100 2012
DAMA/LIBRA 2008
Energy [keVee
] →
rate
dif
fere
nce
[co
un
ts/k
g/k
eV/d
] →
fits on data→
solid line:best fit
dashed:90% UL
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November 27, 2013 Kai Martens, Kavli IPMU, @ Osaka City University 41
XMASS Pre-Refurbishment Highlightsvery successful technology:
→ highest photoelectron yield in the community: 13.8 PE/keVee
→ very low analysis threshold (without fiducialization)
→ very stable long-term operation without active circulation, i.e. without recirculating through hot getters !!
→ eminently scalable: no drift length limitations
→ first results despite unexpected background
but: surface/materials backgrounds need to be better controlled...
→ detector refurbishment: results to come...
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November 27, 2013 Kai Martens, Kavli IPMU, @ Osaka City University 42
XMASS Detector Refurbishment:
done: we are taking new data
what was done:
- Cu surface cleanup → electropolish to “rm -rf U* Th*”
- Cu ring to cover PMT Al seal
- cover Cu rings with electropolished Cu plate for a flat inner Cu surface (no crevasses...)
duller (lighting aside) brighter
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November 27, 2013 Kai Martens, Kavli IPMU, @ Osaka City University 43
Chemically ElectropolishedEtched
duller (lighting aside) brighter
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November 27, 2013 Kai Martens, Kavli IPMU, @ Osaka City University 44
XMASS 1.5background target: ~10-2 /ton/day/keV
(we have a lot of experience now...)
again: two analyses: - low threshold, full volume:
→ cover all “allowed regions” - 5keV threshold, fiducial volume:
→ reach SI cross section of< 10-46 cm2
start construction in 2014 !tank for active water shield is ready...
improved photocathode geometry:to intercept light from surrounding surface...
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November 27, 2013 Kai Martens, Kavli IPMU, @ Osaka City University 45
ConclusionsXMASS 800kg completed first commissioning phase:
- exceptional light yield: 13.8 PE/keVee
- backgrounds largely understood - detector refurbishment completed:
- serious reduction in Rn exposure during work- inner surface cleaned- inter-PMT spaces covered
→ data taking was resumed with:– refurbished detector– full FADC system
Results (from “old” detector): - light WIMP limit- axio-electric cross section limit- annual modulation analysis
Next: XMASS 1.5 (1 ton fiducial, 5 ton total)