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Masaki Yamashita
XMASS
Masaki Yamashita Kamioka observatory, ICRR, Univ. Of Tokyo
On behalf of XMASS collaboration!WPAS, 21st/Jan/2014
Masaki Yamashita
XMASS Experiment
Xenon MASSive detector for Solar neutrino (pp/7Be)
Xenon neutrino MASS detector (double beta decay)
Xenon detector for Weakly Interacting MASSive Particles (DM)
Dark Matter
Solar Axion/Neutrino
Double Beta Decay
Multi purpose low-background experiment with LXe.
Masaki Yamashita
Outline • Introduction of XMASS
• XMASS 800 kg detector
• Results from Commissioning Run
• Low Mass WIMP
• Solar axion search
• 129Xe inelastic
• Bosonic super-WIMP search
• Refurbishment of Detector
• Future prospects
• Data Analysis after Refubishment
• XMASS 1.5 (1ton fiducial, 5 ton LXe)
commissioning phase
after refurbishment
Masaki YamashitaMasaki Yamashita
PhaseXMASS I
（FV:100kg、Total 1ton）
XMASS II （FV:10ton、24Ton）
Dark MatterSolar Neutrino Dark Matter
DBB2007: Project was funded. 2013〜: Data taking
XMASS 1.5 （FV:1ton、Total 5ton）
2014: (hopefully) start construction
Dark Matter
Masaki YamashitaMasaki Yamashita
Concept of background reductionSelf-shielding
PMT
Single phase! Volume for
Fiducial
more than 3 order of magnitude of background can be reduced by 20cm wall cut.
Blue : γ tracking Pink : whole liquid xenon Deep pink : fiducial volumeLXe
U-chain gamma
Masaki Yamashita
Kamioka Observatory, ICRR, Univ. of Tokyo :K. Abe, K. Hiraide, K. Ichimura, Y. Kishimoto, K. Kobayashi, M. Kobayashi, S. Moriyama, K. Nakagawa, M. Nakahata, N. Oka, H. Ogawa, H. Sekiya, Y. Suzuki, O. Takachio, A. Takeda, M. Yamashita, B. Yang
Kavli IPMU, University of Tokyo: J.Liu, K.MartensKobe University: K. Hosokawa, K. Miuchi, Y. Ohnishi, Y. Takeuchi
Tokai University: K. NishijimaGifu University: S. TasakaYokohama National University: K. Fujii, I. Murayama, S. Nakamura
Miyagi University of Education: Y. FakedaSTEL, Nagoya University : Y. Itow, K. Kobayashi, K. Masuda, H. Takiya , H. Uchida
Sejong University: N. Y. Kim, Y. D. Kim
KRISS: Y. H. Kim, M. K. Lee, K. B. Lee, J. S. Lee
The XMASS collaboration:
Masaki Yamashita
Kamioka Observatory
Masaki Yamashita
Kamioka
YangYang
Seoul
Tokyo
Masaki YamashitaMasaki YamashitaBy courtesy of Dr. Miyoki�
•1000m under a mountain = 2700m water equiv.
•360m above the sea •Horizontal access •Experiment •Super-‐K •KamLAND (Tohoku U.) •KAGURA for interferometer •….
Kamioka Observatory
Masaki YamashitaMasaki Yamashita
Water Tank Xenon Buffer Tank
Distillation Tower
Experimental Hall
LXe Tank
water purification system
Rn: ~ 1mBq/m3!5ton/hour
entrance (clean room)
Masaki Yamashita
XMASS800kg in Kamioka
~1m
φ10m x 10m water shield
- φ10m x 10m ultra pure water shield with 20 inch x 70 PMTs for muon veto
- 642 ultra low background 2 inch PMTs - Largest detector: 835 kg of LXe for
sensitive volume.
RI in PMTActivity per 1PMT(mBq/
238U-chain 0.70+/-0.28
232Th-chain 1.51+/-0.31
40K <5.1
60Co 2.92+/-0.16
10 m
Masaki Yamashita
XMASS Recent Results (commissioning phase)
• Calibration
• Low Mass WIMP search
• Solar Axion search
• WIMP search by Inelastic 129Xe scattering
• Bosonic super-WIMPs
Masaki Yamashita
Detector calibration (KRISS, Sejong University)
Gate valve~5
m
•-Inner calibration is very important for position reconstruction.
3. Sources
57Co
241Am
5 5
energy [keV] Intensity [Hz] Dia. [mm] Outer material
(1) Fe-55 5.9 350 5 brass
(2) Cd-109 22, 25, 88 800 5 brass
(3) Am-241 59.5 485 0.17 SUS
(4) Co-57 122 68 (KRISS side) 0.21 SUS 2012/12/21 26
Theses sources were made by KRISS
13 20
30 30
0.21
mmφ
for 57
Co
sour
ce
OFHC copper rod and source
gate valve
source exchange
OFHC copper rod
stepping motor
Flange for
movedalong z−axis
guide pipe
Calibration systemon the tank top
ID
Figure 5: Calibration system on top of the tank. Source placed on the edge of the copper
rod is inserted into the ID and can be moved along the z axis.
Table 7: Calibration sources and energies. The 8 keV (*1) in the 109Cd and 59.3 keV (*2)
in the 57Co source are Kα X-rays from the copper and tungsten, respectively, used for
source housing.
Isotopes Energy [keV] Shape
55Fe 5.9 cylinder
109Cd 8(*1), 22, 58, 88 cylinder
241Am 17.8, 59.5 thin cylinder
57Co 59.3(*2), 122 thin cylinder
137Cs 662 cylinder
21
Masaki Yamashita
Detector calibration
122keV
136keV59.3keV of W
~4% rms
0
0.2
0.4
0.6
0.8
1
0 500 1000 1500 2000 2500
Eve
nts
(nor
mal
ized
)
total nPEs
Even
ts (n
orm
aliz
ed)
total nPEs
real datasimulation (MC)
Figure 7: Observed nPE spectrum using the 57Co source at z = 0 cm (red dots). Simulated
spectrum is shown as blue histogram.
PMT copper holder and the aluminium strip on the PMT window, refrac-325
tive indices of liquid xenon and the quartz PMT window, and the reflection326
and absorption probabilities at a PMT photo-cathode. These parameters327
were tuned so that the observed numbers of PEs (nPEs) in each PMT in the328
simulated samples reproduce those in the data for various source positions.329
Figure 7 shows the nPE spectrum observed using the 57Co source at z = 0 cm330
and the MC result. The nPE distribution was reproduced well by the MC,331
and a high light yield, 14.7 ± 1.2 PE/keV was obtained.332
The MC tracks the incident particles and any energy deposited through333
various interactions. From the deposited energies in each vertex, scintillation334
photons are generated by taking into account the dependence on energy and335
nature of the depositing particle, implementing a realistic, non-linear scintil-336
lation efficiency [14]. This effect results in non-linearity of the scintillation337
efficiency. The energy distribution of the scintillation photons is based on338
the measured value [15] which is a Gaussian distribution with a mean value339
23
0
0.2
0.4
0.6
0.8
1
0 20 40 60 80 100 120 140
Even
ts (n
orm
alize
d)
reconstructed energy [keVee]
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
-40 -30 -20 -10 0 10 20 30 40
Norm
alize
d
reconstructed z [cm]
real datasimulation (MC)
real datasimulation (MC)
Even
ts (n
orm
aliz
ed)
Even
ts (n
orm
aliz
ed)
Reconstructed position (z) [cm]
Reconstructed energy [keVee]
Figure 9: Energy spectra reconstructed using the 57Co source at z = 0 cm (upper) and ver-
tex distributions reconstructed using the same source at z = −40, −30, ..., 40 cm (lower).
26
Position
Total PE
•-Highest Light Yield 14.7 PE/keV •-Good agreement between data and.
Masaki Yamashita
Recent Result of XMASS
xe100
xe10 (S2)
EDW IICDMSII Ge
XMASS
Physics Letters B 719 (2013) 78-82
Light mass WIMPl 835 kg x 6.7 days data!•Full volume analysis with 835 kg LXe. (without fiducial volume cut.) •Hight Light Yield 14.7 PE/keV •Eth 0.3 keVee (scaled by 122keV) • Scintillation Efficiency (Leff ) from XENON (Phys. Rev. Lett. 107 (2011) 131302)
!"
!#
!$
!%
!&
!'
!" !"(' !# !#(' !$
)*+,-./012/34/35655
5,5742!8356559
:(;"!012.!!!<%'!34!=''>#(&!34"012.?
#<@56!!!AB"C,D#('$!#"C&#)E$
#$@56!!!AB"C,D$(<&!#"C&#)E$
!;@56!!!AB"C,D&(&&!#"C&")E$
Figure 7: Simulated WIMP energy spectra in the XMASS detector assuming the maximumcross section that provides a signal rate no larger than the observation in any bin above0.3 keVee.
12
7GeV
18GeV
12GeV
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Masaki Yamashita
Solar Axion search
Our data
ma=
Max allowed
l -Solar Axion Produced in the Sun and detected in the detector. l -strong constraint in 10-40keV.
Phys. Lett B 724 (2013) 46 arXiv: 1212.6153
gaee
Axio-‐electric effect
gaee
Bremsstrahlung and Compton effect
10-13
10-12
10-11
10-10
10-9
10-8
10-7
10-6
10-5
10-4
10 -2 10 -1 1 10 10 2 10 3 10 4 10 5 10 6 10 7mass (eV)
g aee
Red GiantsKSVZ
DFSZ
solar neutrino
Si(Li)
169Tm
o-Ps
reactors beamdump
Ge XMASSEDELWEISS
Masaki Yamashita
129Xe Inelastic scattering
✓Dark Matter Search by 129Xe inelastic scattering
✓ Cuts are optimized to have best S/N in 30-80keV. - 10-30, 80-100keV calibration data were used.
✓ 3pb at 100 GeV.
✓ to be submitted
Excitation cross section
excitatio
n cros
s section[pb
]
WIMP mass[GeV/c2]
2000 DAMA/LXe
preliminary
XMASS upper limit(90%C.L.)
110 102 103
10
data MC
scaled energy (13.9PE/keV)20 40 60 80 100
1
10
210
310
410
510
610
events/keV
20 40 60 80 100energy(keV)
bfr cut aft cut
applied cuts: pre-selecion radius cut timing cut band cut
100GeV WIMP
WIMP�Xe129� Nuclear0recoil�
WIMP%Xe129�����Xe129� WIMP� Xe129�
40keV0gamma�
τ=0.97ns�
Nuclear0recoil�
��� ����
WIMP�Xe129� Nuclear0recoil�
WIMP%Xe129�����Xe129� WIMP� Xe129�
40keV0gamma�
τ=0.97ns�
Nuclear0recoil�
��� ����
Inelastic
excitation
deexcitation
not χ + N →χ*+ N
Masaki Yamashita
Bosonic super-WIMPs
✓Candidate for Warm Dark Matter - Search for Pseudoscalar, vector boson
✓mono-energetic peak at the mass of particle like photoelectric interaction.
✓This is the first contain from experiment. - same analysis can be done for Pseudoscalar boson
✓To be submitted
photoelectric like interaction
1
10
102
103104
105
106
events/keV
v
Masaki Yamashita
Refurbishment
Masaki Yamashita
XMASS Refurbishment to reduce background
PMT
quartz window
Al seal
✓What kind of background in commissioning Run ?
- Radioactivity in PMT’s Al seal(210Pb, 238U ~a few Bq) ‣ Activity in U-chain is not
equilibrium. ‣ Those background deposit
energy near the Al (dead zone) and make it difficult for position reconstruction.
‣ How do we solve this problem ? ‣ Cover around Aluminum seal
by Copper ring and protect from scintillation light and low energy beta from dead zone.
ATM Data ~6day data Surface 210Pb PMT Al 235U-‐231Pa PMT Al 210Pb PMT Al 232Th PMT Al 238U-‐230Th PMT gamma
Masaki Yamashita
XMASS Refurbishment✓Copper rings were mounted to
minimize the space between PMTs. ✓We evaporated high purity Al on the
side of PMT window. ✓On top of copper ring, thin copper plate
attached to protect scintillation light between copper rings.
20
PMT
quartz window
PMT
quartz window
Cu PlateCu Ring
Al sealIn LXe
evaporated high purity Al
Masaki Yamashita
Copper plateAfter RFBBefore RFB
Masaki Yamashita
RFB improve ?
✓Quick look by using simple parameter maxPE/totalPE to see the how the events distributed in the detector.
✓maxPE/totalPE is getting bigger if the event R is larger. (except dead volume like between PMTs.)
Total PEsmaximum PE in one PMTmaxPE/totalPE =
RFBの成果を簡単にチェックするためのパラメータ (内側、外側事象を切り分ける)
small maxPE/totalPE
small maxPE/totalPE
Masaki Yamashita
We did it.
✓Obviously, the background from - ~ 1/10 background reduction by this RFB work. (50~100p.e.) - Those events easily recognized by max/Total PE distribution and more than one order of magnitude reduction can be achieved even by this simple cut.
✓Position reconstruction based on PE and Timing will improve the situation.
before RFB after RFB
totalPEmax
PE/totalPE
totalPE
max
PE/totalPE
normalize by live time
ADC saturation
big improvement
BG from dead volume
Cherenkov cut onlyno position reconstruction yet.
Masaki Yamashita
Modulation analysis
✓only 136.1 days data gives comparable result as DAMA/LIBRA.
✓1 years live time data is enough to cover DAMA/LIBRA.
✓We are ready to take those data.
•XMASS commissioning phase •136.1 live time days x 835 kg (2010.12 ~ 2012.5)
➡=> 0.31 ton year (DAMA/LIBRA 1.33 ton year, 14 cycles）
➡software Eth = 1 keVee, (most of the runs were taken ~1keV Eth)
3sigma
XMASS 90CL
Energy [keV]0 2 4 6 8 10 12 14 16 18 20R
esid
uals
[cou
nts/
day/
kg/k
eV]
-0.06
-0.04
-0.02
0
0.02
0.04
0.06152.5 day
XMASS 0.31 ton x year!DAMA/LIBRA 1.33 ton x year!arXiv:1308.5109 Preliminary
Masaki Yamashita
Next phase: XMASS 1.5
convex PMTflat PMT
Scintillation
photocathod
quartz
-1ton fiducial, 5 ton total!- <10-46cm2 at 100 GeV.!-Inherit current water shield !-XMASS 1.5 design study is on going.!- Convex PMT will solve the problem of surface events more effectivly.!- Prototype PMTs will be delivered.
Masaki Yamashita
Summary✓Commissioning Data
✓ low mass WIMP
✓Solar Axion
✓ Inelastic 129Xe
✓bosonic Super WIMP
✓Refurbishment of Detector
- Finish in Oct 2013.
- Start taking data.
- Coming data looks promising !
✓Future
✓Annual modulation search.
✓Fiducial volume analysis after RFB.
✓XMASS1.5 design is on goin.
