xmass experiment -

XMASS experiment

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Yongpyong-High1 2015: Joint Winter Conference on Particle Physics, String and Cosmology

High1 resort, Korea, Jan. 25–31, 2015 28th of Jan. 2015

Atsushi Takeda for XMASS Collaboration

Contents

1. Direct DM search with LXe detector 2. XMASS project 3. Results from XMASS-I commissioning run 4. Refurbishment of XMASS-I 5. XMASS-1.5 6. Summary

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1. Direct DM search with LXe detector

Characteristic of liquid xenon z -100 degree Celsius: easy to liquefy and handing. z High density (~3 g/cm3): compact detector. (~2m dia. for 10t scale) z Large Z (= 54): effective self shielding for external BG. z Large photon yield: low threshold can be achieved. z Scintillation wavelength ~175nm: directly detected by PMTs z Purification: absorption material (ex. water and oxygen) can be purified by Zr getter.

Ligh

t yie

ld (p

hoto

ns/k

eV)

Abso

rptio

n Co

effic

ient

(cm

-1)

4

Direct DM detection WIMPs elastically scatter off nuclei in target material, producing nuclear recoils.

Dark Matter （WIMP）

Deposit Energy Deposit energy (a few keV)

Dark matter (WIMP)

Spin independent case: → Large A gives higher event rate.

z Event rate and cross section

R0 : event rate F: nucleus form factor

Maxwellian distribution for DM velocity is assumed. v0 : dispersion v: velocity onto target vE: Earth’s motion around the Sun

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Expected WIMP event rate

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10-3

10-5

10-1

Energy [keVee]

10-2

10-4

10-6

Dark matter signal (50GeV/100GeV, Q.F.=0.2) 10-45 cm2

10-42 cm2

0 50 100

Gamma-ray background -(20cm shield, fid. 100kg)

Neutron background -(fid. 100kg)

dru

[eve

nts/

keVe

e/kg

/day

]

→ Xe (A=131) is one of the best target 6

Single phase vs. double phase LXe detector z Single phase :

– DM signal (uniformly distributed) are identified by fiducial volume analysis.

– Also PSD may reduce background. • Scintillation decay time difference

between nuclear recoil (DM) and electron recoil can be used.

z Double phase :

– DM signal (nuclear recoil) are identified by fiducial volume and

ionization(S2) / scintillation(S1) ratio.

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Advantage of single phase detector z Simple and good scalability No need for complicate structure like an HV z BG reduction by self-shielding Effective even for neutron BG (lower figure) z High light yield & low energy threshold (XMASS-I: 14.7 pe/keV and 0.3 keV threshold) z Sensitive for e/γ events

1MeV neutron

φ2.5m LXe detector Black: all events Blue: 2 < E(keVee) < 5 keV Red: 2 < E(keVee) < 10 keV

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XMASS-2 (φ2.5m, 10 ton FV)

Current DM experiment with LXe detector

XENON100/1T

XENON100: 161kg xenon 50kg FV Continue data taking 2014 XENON1T: Commissioning phase 2015–

LUX

350kg xenon 118kg FV First result: PRL 112, 091303 (2014) using Apr–Aug 2013

PandaX

PandaX-I 37kgFV x 17.4days First result: arXiv:1408.5114 using May–Jul 2014 PandaX-Ib 300kgFV x 180days

Double phase

XMASS

XMASS-I is ongoing since 2010 835kg xenon 100kg FV

Single phase

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2. XMASS project

The XMASS Collaboration

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Kamioka Observatory, ICRR, the University of Tokyo: K. Abe, K. Hiraide, K. Ichimura, Y. Kishimoto, K. Kobayashi, M. Kobayashi, S. Moriyama, M. Nakahata, T. Norita, H. Ogawa, H. Sekiya, O. Takachio, A. Takeda, M. Yamashita and B. Yang Kavli IPMU, the University of Tokyo: J.Liu, K.Martens and Y. Suzuki Kobe University: R. Fujita, K. Hosokawa, K. Miuchi, Y. Ohnishi, N. Oka and Y. Takeuchi Tokai University: K. Nishijima Gifu University: S. Tasaka Yokohama National University: S. Nakamura Miyagi University of Education: Y. Fukuda STEL, Nagoya University: Y. Itow, R. Kegasa, K. Kobayashi, K. Masuda and H. Takiya Sejong University: N. Y. Kim and Y. D. Kim KRISS: Y. H. Kim, M. K. Lee, K. B. Lee and J. S. Lee Tokushima University: K.Fushimi

June 2014

11 institutes ~40 physicists

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XMASS project

835 kg, 100 kg Fiducial volume (FV) φ80 cm, 642 PMTs Since 2010 Nov. ・ Dark matter search

XMASS-II

25 ton, 10 ton FV φ2.5 m Multi purpose ・ Dark matter ・ pp solar neutrino ・ 0n2b decay

Y. Suzuki, hep-ph/0008296

XMASS-1.5

5 ton, 1 ton FV (x 10 of XMASS-I) φ1.5 m, ~1000 PMTs ・ Dark matter search

XMASS-I

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Now

Site KamLAND

Super-K

XMASS (Lab-C)

CANDLES

IPMU Lab1 CLIO NEWAGE

Lab2/EGad

Tokyo

Kamioka Mine

Kamioka Mine

~1000m underneath Mt. Ikenoyama. (2700 m.w.e.)

Japan

Kamioka mine Lab-C 13

XMASS-I setup

10m

11m

~ 1.2m 642 PMTs

OFHC copper vessel

835kg liq. xenon

Water tank Refrigerator

72 20inch PMTs (veto)

Elec. hut

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Reservoir

z Detail: NIMA 716 (2013) 78 z Single phase LXe detector. z World’s largest (835kg) dark matter detector z Low threshold (0.3keVee) z High light yield (14.7 pe/keV) z Commissioning data taking (2010/10–2012/05) z Resuming of data taking after refurbishment (2013/11～)

XMASS-I detector

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Detector calibration (inner)

Stepping motor

Linear and rotary motion feed-through

Top photo tube

~5m Gate valve

Φ0.21 mm for 57Co source

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RI Energy [keV] [Hz] dia. [mm]

(1) Fe-55 5.9 ~5 5

(2) Cd-109 8, 22, 25, 88 ~800 5

(3) Am-241 17.8, 59.5 ~500 0.17

(4) Co-57 59.3, 122 ~30 0.21

(5) Cs-137 662 ~200 5

(3), (4) : Micro-source made at KRISS. Diameters of source are much shorter than attenuation length of gamma in liquid xenon to minimize the shadowing effect from source itself

Source rod

z Light yield and position reconstruction

Active region is concentrated on 1.8 mm edge region

0.21mm 4mm

19mm

Detector response for a point-like source (~WIMPs)

z 57Co source @ center (z=0cm) gives a typical response of the detector. z Large light yield, 14.7 p.e./keVee (Ù 2.2 for S1 in XENON100) z The pe dist. well as vertex dist. were

reproduced by a simulation well.

Reconstructed vertex data MC

122keV

136keV 59.3keV of W

~4% rms

+15V

57Co micro source is moved inside the detector along z axis

data MC

Z [c

m]

Z [c

m]

Total photo electron (z=0cm)

z

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History of XMASS-I

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2010 2011 2012 2013 2014 2015

Const- ruction

Commissioning Run Data taking Refurbishment Data taking

Dec. May Nov.

Several physics results from this term were published later

Sep. 2010

Main BG source was identified, and it was cover with copper ring and plate.

Stable and long term data taking is ongoing.

Physics results of XMASS-I

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z Light WIMP search, Phys. Lett. B 719 (2013) 78 z Solar axion search, Phys. Lett. B 724 (2013) 46 z Bosonic Super-WIMPs, Phys. Rev. Lett. 113 (2014) 121301 → Chosen as Editor’s suggestion z Inelastic scattering on 129Xe, PTEP 2014, 063C01

z Seasonal modulation with full volume of LXe z Fiducial volume analysis for heavy WIMPs z Double electron capture of 124Xe

Published

Results to come soon

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3. Physics results from XMASS- I commissioning run

Low mass WIMPs search PLB 719 (2013) 78-82

z Full volume (835 kg) analysis z 6.80 days in 2012 Feb. z 5591.4 kg day exposure z 0.3 keVee threshold

Energy [keVee]

Coun

ts/d

ay/k

g/ke

Vee

0 0.5 1 1.5 2 0

1

2

3

4

5

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Solar Axion search

Our data

ma=

50 keV

Max allowed

z Axion is a hypothetical particle to solve the strong CP problem z Produced in the Sun by bremsstrahlung and Compton effect, and detected in the detector by axio-electric effect. z XMASS is suitable to search because of a large mass and low BG

gaee

Bremsstrahlung and Compton effect gaee

Axio-electric effect

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PLB 724 (2013) 46-50

Bosonic super-WIMP (1/3)

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PRL 113 (2014) 121301 z Search for lighter and more weakly interacting particles is attracting attention, because

• So far no evidence of SUSY particles at the LHC. • Expectation on the structure on garactic scales of the CDM scenario is richer than observed.

z Bosonic super-WIMPs search (M. Pospelov et. al., Phys. Rev. D 78 115012 (2008), J. Redondo and M. Postma, J. Cosmol. Astropart. Phys. 02 (2009) 005 )

• A lukewarm dark matter candidate, and lighter and more weakly interacting particles than WIMPs. • Deposit energy in a target material would essentially equivalent to the super-WIMP rest mass. • Search for pseudoscalar and vector boson (called as dark, para, or hidden photon) with photoelectric-like interaction. • For vector boson, no experimental constraint so far.

v or a Photoelectric-like interaction


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z 166 days and 41 kg fiducial volume data. z Search for mono-energetic peak at mb (the rest mass of a bosonic super-WIMP) using various cuts optimized for each mb. ((1) pre-selection, (2) reconstructed radius (R<15cm) cut, (3) timing cut, (4) pattern cut) z The remaining event rate of O(10-4) /day/keVee/kg is the lowest ever achieved and consistent with expected BG from 214Pb.

D.C. Malling’s

thesis (2014)

XMASS

↑BG level of each experiment (before separation for nuclear recoil in 2–phase DM search detector)


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z Constraint on coupling constant. z For vector bosonic super-WIMPs, the first direct search in the 40–120 keV range. The limit excludes the possibility that such particles constitute all of dark matter. The most stringent direct constraint on gaee thanks to the low BG in this energy region.

Pseudoscalar

Vector boson

Inelastic scattering DM search (1/2)

WIMP

Xe129

39.6 keV gamma

Nuclear recoil

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z c + 129Xe Æ c + 129Xe* 129Xe* Æ 129Xe + g (39.6keV)

z Natural abundance of 129Xe: 26.4%

PTEP 063C01 (2014) z WIMPs would cause inelastic scattering on 129Xe. Nuclear recoil as well as 39.6 keV g ray emission are expected. z Peak search at 39.6 keV with various cuts are used. Reconstructed radius cut (R<15cm), timing cut, and pattern cut.

(1) Pre-selection (2) (1) & radius cut (3) (2) & timing cut (4) (3) & band cut

Observed data (165.9 days)

Signal MC for 50GeV WIMP

Inelastic scattering DM search (2/2)

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50GeV WIMPs an upper limit of 3.2pb at 90% C.L.

Red: XMASS (90% C.L. stat. only) Pink band: XMASS (w/ sys. error) Black: DAMA LXe 2000 (90% C.L.)

z 41 kg fiducial volume (129Xe: 11 kg) w/o BG subtraction z Better limit than DAMA for > 50 GeV WIMPs z Another way for study on SD interaction.

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4. Refurbishment of XMASS-1

Identification of BG source z Dominant BG in the commissioning run is originated from “detector surface”. z RI in PMT Al seal and on surface of PMT and PMT holder. z Such events are likely to be reconstructed inside the fiducial volume, because photons are hardly detected in neighboring PMTs.

z Refurbishment from May 2012 to Nov. 2013 z PMT Al seal were covered by copper ring and plate to reduce the beta and X-ray and make a simple and flat surface. z Electro-polish is applied to those ring, plate and PMT holders.

Red arrows: track of scintillation photons

Refurbishment

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XMASS Refurbishment Before After

+ Copper plate

Copper ring mounting

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Current status (1/3)

XMASS commissioning

XMASS refurbishment

Energy spectrum for entire volume

Coun

ts/d

ay/k

ev/k

g

0.1

1.0

z Restarted data taking from Nov. 2013. z Quick check of energy spectrum indicates one order reduction of BG from commissioning run data. z ATM (charge and timing) → FADC analysis. z Energy threshold is reduced from 1keV to 0.3 keV. z Already accumulated 277 days data for WIMP search till Dec. 2014. z Using this data, physics analyses including WIMP search with fiducialization

and seasonal modulation are on-going.

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Current status (2/3)

3 x10-40cm2

1.9x10-41cm2

No modulation

Simulation

Expected modulation in XMASS for 8 GeV WIMP

0.3-0.4keV

z Seasonal modulation analysis • World’s largest mass (832 kg after refurbishment): 1 year data of XMASS ~ 14 years data of DAMA/LIBRA 0.8 ton*year ~ 1.33 ton*year → Current statistics is already half of DAMA/LIBRA data. • Low energy threshold: 0.3 keVee. • For several physics (DM, axion) w/o PID. • The results for 1 year data will come soon.

Prospects after refurbishment for full volume

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Current status (3/3) z Fiducial volume (FV) analysis

・292.7days (live time) data were used. ・Surface events sometimes miss-reconstructed as events happened inside the FV. ・Conservative limit assuming all remaining events are caused by WIMP without BG subtraction are derived. sSI < 2.7x10-43 cm2 (50GeV WIMPs). Possible all the systematic errors are taken into account. ・Remaining BG sources are identified. Results with BG subtraction is now being prepared.

Effic

ienc

y [%

]

25

50

0 0 2 4 6 8 10

0 2 Reconstructed energy [keVee] 4 6 8 10 12 14 16

[/da

y/kg

/keV

ee] Real data (292.7days)

50 GeV WIMP MC 100 GeV WIMP MC

90 % C.L. limit w/o BG subtraction

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5. XMASS 1.5

XMASS-1.5 z Total 5 ton (FV 1 ton) z BG reduction: - No dirty Al seal - Less surface 210Pb (< 1/100) z New PMT with round shape window to identify surface event is being developed. MC study for evaluation of miss-reconstruction rate is on-going.

Round shape window

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PMTs for XMASS-1.5 Scintillation light from

the surface can be detected.

PMTs for XMASS-I High probability to miss catching

the photons from the surface.

Dotted line = photo cathode Dotted curve = photo cathode

Red arrows: track of scintillation photons

Less surface 210Pb (<1/100)

z Environment controlling during machining of detector (1) All the works should be done under Rn free air with Rn concentration of ~10mBq/m3 (usually 20Bq/m3) (2) All the surfaces should be cleaned by electro-polishing (EP) z Controlling of Rn exposure after EP (1) Minimization during machining: Optimization of all process (2) Minimization during storage: Packed with Rn barrier sheet (EVOH) and conductive bag. (3) Less Rn environment during assembling (<10mBq/m3): Rn removing device with electro-static collection is being developed. (Rn decay products (especially, 218Po) tend to have positive charge and collected with high voltage) 36

PMT with round shape window

zMass-production is OK. zOptimization of shape and cost-cutting are being concerned. z Less radio-active impurities. z MC study of miss-reconstruction rate is being evaluated: Reduction rate of < 10-5 at 2.5keV was obtained for events occurred in the side of window.

Round shape window

・3 PMTs around event vertex detect 40–50% of pe. ・Cut criteria: Fraction of pe in 3 PMTs > 10%

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Summary z XMASS-I is the world’s largest (835kg) and low threshold

(0.3keVee) detector for dark matter search. z Physics results from commissioning data with the full advantage

of sensitivity to e/g events as well as nuclear recoil with low BG at a few 10’s keV at a level of 10-4 /day/kg/keVee.

z Current status.

• The refurbishment of detector completed and data taking resumed in Nov. 2013. • One order reduction of BG from commissioning run data.

z Future • Designing of XMASS-1.5 is on-going. • Aim to sSI < 10-46 cm2 (>5keV) for fiducialization.

• Low mass WIMP search (PLB 719(2013)78) • Solar Axion search (PLB 724 (2013) 46) • Bosonic super-WIMPs (PRL 113, 121301 (2014)): For vector boson, the first direct search in the 40–120 keV range. • Inelastic scattering WIMP search (PTEP 063C01 (2014))

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Backup

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Remaining background in XMASS-I

z BG level was 2 order of magnitude larger than expectation z It was same level with DAMA and CoGeNT z The origin of BG for ≧ 5 keV were confirmed (lower figure) z Also for < 5 keV, likeliest candidate (Gore-Tex) was identified z “Surface events” are dominant in both energy regions z To reduce these surface events, refurbishment is in progress.

Full volume

5 20 10 15 Rate

[/da

y/ke

Vee/

kg] ● Black line: Real data

● Colored histogram: BG (MC) Surface Cu 210Pb PMT Al 235U-231Pa 210Pb 232Th 238U-230Th PMT gamma Gore-Tex 210Pb Gore-Tex 14C

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Origin of BG in XMASS-I

Al seal

zMain BG source (≧5keV)

z BG candidate (< 5keV) z In refurbishment, Al seal will be covered by copper rings and GORE-TEX will be removed z In XMASS-1.5, Al seal will be replaced with ultra pure one

XMASS Refurbishment work z Purpose of Refurbishment: - Confirmation of BG reduction by shielding of scintillation light originated from PMT Al - Also reducing 210Pb (2nd largest component in BG) with electro-polishing and special clean environment. z Expected BG level: Al and surface BG are reduced to same level as PMT gamma BG. (~10-44 cm2 for 100 GeV WIMP with fiducialization) z In next step (XMASS-1.5), it will be replaced with new PMT.

After installation of ring

Before installation of ring

w/o ring

w/ ring reduction

Even

ts/d

ay/k

eV/k

g

Energy (keV)

Full volume

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Micro-source development for XMASS experiment

Detector calibration (outer)

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z Neutron (252Cf) ・Response for nuclear recoil ・PSD study

z g (60Co) ・Stability of light yield is monitored weekly ・Easy handling and short data taking (~2hours)

Pipe for gamma source

Pipe for neutron source

124Xe (2n) double electron capture (1/2)

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124Xe (g.s., 0+) + 2e-Æ 124Te (g.s., 0+) +2n + 2.866MeV

Natural xenon has 124Xe isotope (0.1%) which is one of the candidates of DEC nuclei.

z Two orbital electrons are captured by two protons in the 124Xe nucleus and two neutrinos are emitted simultaneously.

z Two neutrinos will escape from the detector. z Recoil energy of 124Te is ~30eV at maximum,

which is negligible. z X-rays and Auger electrons are emitted.

124Xe (2n) double electron capture (2/2)

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Model T1/2 (2n 2e) (yr) Reference

QRPA (0.4-8.8)x1021 J.Suhonen, J. Phys. G40, 075102 (2013)

QRPA (2.9-7.3)x1021 M.Hirsch et al., Z.Phys. A347, 151-160 (1994)

SU(4)st (7-17.7)x1021 O.A.Rumyantsev and M.H.Urin, Phys. Lett. B443, 51 (1998)

PHFB (7.1-18.0)x1021 S.Singh et al., Eur.Phys. J. 33, 375-388 (2007)

PHFB (61.4-155.1)x1021 A.Shukla et al., J. Phys. G34, 549-563 (2007)

MCM (390-986.1)x1021 M.Aunola and J.Suhonen, Nucl. Phys. A602, 133 (1996)

z Theoretical prediction on 124Xe DEC half life

Detector T1/2 (2n 2K) (yr) Reference

Gas proportional counter >1.1x1017 (90%CL) Yu.M.Gavrilyuk et al., Phys. Atom. Nucl. 61, 1287 (1998)

Gas proportional counter >4.67x1020 (90%CL) Yu.M.Gavrilyuk et al., arXiv:1404.5530 (2014)

XENON100 (sensitivity?) >1.66x1021 (90%CL) D.-M.Mei et al., Phys. Rev. C89, 014608 (2014)

z Experimental results

129Xe inelastic scattering DM search

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z In the case of 129Xe: The expected event rate from inelastic scattering is one order magnitude smaller than one from elastic scattering. If BG level around 40 keV is more than one order of magnitude smaller than one around a few keV region, inelastic search has better sensitivity than elastic search.

Elastic scattering search region

Inelastic scattering search region

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K. Kobayashi, Kamioka seminar, Nov. 19th 2014

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K. Kobayashi, Kamioka seminar, Nov. 19th 2014


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Pseudoscalar

Vector boson

XENON100: E. Aprile et al. (the XENON100 Collaboration), arXiv:1404.1455 EDW-II: E. Armengaud et al. (the EDELWEISS-II Collaboration), J. Cosmol. Astropart. Ohys. 11 (2013) 067.

Coupling constant required to reproduce the observed dark matter abundance including resonance effect

Constraint from the He-burning lifetime in horizontal Branch (HB)

Upper limit

XENON

z Dark matter Results from 100 Live Days of XENON100 data z E. Aprile et. al., (XENON100 Collaboration) Phys. Rev. Lett. 109, 181301 (2012)

z On the spin-dependent sensitivity of XENON100 z Mathias Garny wt. al., Phys. Rev. D87, 056002 (2013)

z First axion results from the XENON100 experiment z E. Aprile et. al., Phys. Rev. D90, 062009 (2014)

XENON10 (Low mass WIMP, S2 only)

XENON100

z J. Angle et. al., (The XENON10 collaboration), Phys. Rev. Lett. 107, 051301 (2011)

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LUX z First Results from the LUX Dark Matter Experiment at the Sanford Underground Research Facility z D. S. Akerib et. al., (The LUX Collaboration), Phys. Rev. Lett. 112, 091303 (2014)

FV: 118 kg From Apr. to Aug., 2013 (85.3 live days) 7.6×10-46 cm2 at 33 GeV/c2 (90% CL)

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PandaX z First dark matter search results from the PandaX-I experiment z Mengjiao Xiao et. al., (The PandaX Collaboration), arXiv: 1408.5114

FV: 37 kg From May 26 to July 5, 2014 (17.4 live days) 3.7×10-44 cm2 at 49 GeV/c2 (90% CL)

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