Status of XMASS experiment

Cygnus 2013@Toyama2013/06/05

Nagoya univ. H.Uchidafor XMASS collaboration

1

Overview

2

835 kg, 100 kg Fiducial volume (FV)

80 cm, 642 PMTsφ

XMASS-II

25 ton, 10 ton FVφ2.5 m　・ Dark matter　・ pp solar neutrino　・ 0 2 n b decay

XMASS-1.5

5 ton,1 ton FV1.5 m, ~1000 PMTsφ

XMASS-I

・ Dark matter search

•A purpose of XMASS-I and 1.5 experiment is dark matter search.•Commissioning data was taken with XMASS-I at the Kamioka Observatory in Japan between Nov. 2010 and May. 2012. And now refurbishment work is on going.•XMASS-II has multi purpose of dark matter, pp solar neutrino and 0 2 decay.ν β

Y. Suzuki, hep-ph/0008296

800kg detector

• XMASS is a single phase detector with ultra pure liquid xenon.

• Background is reduced by a self-shielding of liquid xenon.

• This detector has high light yield (~14p.e./keV) & low energy threshold (~0.3keVee).

• This detector is sensitive for electromagnetic signals.

3

Detector configuration

10m

11m

~ 1.2m642PMTs

OFHC coppervessel

835kgliq. xenon

Water tank

Refrigerator

72 20inch PMTs (veto)

Elec. hut

4

700L reservoir

There is a this detector at Kamioka observatory.

Source calibration

5

Steppingmotor

Linear and rotary motionfeed-through

Topphototube

~5m

Gatevalve

5

4mmf0.21mm f for 57Co source

Source rod with a dummy source

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

(1) Fe-55 5.9 350 5

(2) Cd-109 8(*1), 22, 25, 88 800 5

(3) Am-241 17.8, 59.5 485 0.21

(4) Co-57 59.3(*2), 122 40 0.21

(5) Cs-137 662 200 5(*1) Ka X-rays from the copper used for housing.(*2) Ka X-rays from the tungsten used for housing.

•Calibration sources are used for checking detector response.• The sources can be moved along the vertical axis in the detector.

•We can use one of five sources.•Right hand animation shows a procedure of calibration data taking. First, installation of a source to a calibration rod, opening the top PMT, and insertion of the rod.

Calibration data

• Calibration data で real data を

6

Real data MC

57Co calibration data (122keV)

４０３０

40

30

20

10

0-10

-20

-30

-40

4030

20

10

0-10

-20

-30

-400 10 20-10-20 0 10 20-10-20

y [cm]y [cm]z

[cm

]

Background• Background level of XMASS-I is a few event/day/keV/kg [dru]

without fiducualization.• It is similar level with DAMA and CoGeNT.• The origin of BG for more than 5 keV were almost identified

(lower figure). Also for less than 5 keV, Gore-Tex may explain the events.

• Events originate at the inner surface must explain major part of the observed events..

77

Full volume

5 2010 15dru

[/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

PMT 写真とアルミの位置の説明

Light mass WIMP search

8

Full volume (835 kg) analysis6.70 days×835kg in 2012 Feb. 0.3 keVee threshold

Energy [keVee]

Coun

ts/d

ay/k

g/ke

Vee

0 0.5 1 1.5 20

1

2

3

4

5

solar axion search

9

Our data

ma=

50 keV

Max allowed

Axion is a hypothetical particle to solve the strong CP problemProduced in the Sun and detected in the detectorXMASS is suitable to search because of a large mass and low BG

Bremsstrahlung and Compton effect

gaee

gaee

Axio-electric effect

WIMP-Xe129 inelastic scattering

他の非弾性散乱実験についての言及。

I127 を使った（ DAMA 、 PICORON ）？論文があるか見ておくこと。

Inelastic の図

10

Reduction of surface background

11

Optimization of the cut parameters

12

Systematic error

13

Upper limit for the inelastic cross section

14

1.5

15

Refurbishment

16

Summary

17

Back up

18

Cross section of DM100GeV

19

f

MR

fNv

MR

WI

TW

WIasI

3710758.3

= 3.758×10-37 ×6.74×100/0.3 = 8.4×10 34 ‐ cm2 (8.4×102pb)

(explanation of this function in backup slide)

NA of Xe129

# of events of no cut in DM100GeV MC are 82625.If these events occur in 55.6days,

Calculation of cross sectionDM100GeV:82625/835/0.264/55.6 = 6.74 event/kg(Xe129)/day

Scaled energy(13.9PE/keV)

Even

t/ke

V

When cross section is 8.4×102pb, inelastic events by DM100GeV occur 82625 events in 55.6days.

Even

t

Reconstructed R (cm)

Cross section of DM200GeV

20

f

MR

fNv

MR

WI

TW

WIasI

3710758.3

= 3.758×10-37 ×6.74×200/0.5 = 1.0×10 33 ‐ cm2 (1.0×103pb)

(explanation of this function in backup slide)

NA of Xe129

# of events of no cut in DM200GeV MC are 82640.If these events occur in 55.6days,

Calculation of cross sectionDM200GeV:82640/835/0.264/55.6 = 6.74 event/kg(Xe129)/day

When cross section is 1.0×103pb, inelastic events by DM200GeV occur 82640 events in 55.6days.

Scaled energy(13.9PE/keV)

Even

t/ke

V

Even

t

Reconstructed R (cm)

Cross section of DM400GeV

21

f

MR

fNv

MR

WI

TW

WIasI

3710758.3

= 3.758×10-37 ×6.70×400/0.53 = 1.9×10 33 ‐ cm2 (1.9×103pb)

(explanation of this function in backup slide)

NA of Xe129

# of events of no cut in DM400GeV MC are 82175.If these events occur in 55.6days,

Calculation of cross sectionDM200GeV:82175/835/0.264/55.6 = 6.70 event/kg(Xe129)/day

When cross section is 1.9×103pb, inelastic events by DM400GeV occur 82175 events in 55.6days.

Scaled energy(13.9PE/keV)

Even

t/ke

V

Even

t

Reconstructed R (cm)

Reduction of best parameter set

22

Energy(keV)

# o

f eve

nts

Live time: 55 days

cut # of events(20-

100keV)

reduction

No cut 2094840 1

(1):pre-selection 1651610 0.79

(2) : (1) + volume cut

2877 1.4e-3

(3) : (2) + timing cut

417 2.0e-4

(4) : (3)+ band cut 7 3.3e-6cut # of events

(30-65keV)

reduction

No cut 990692 1

(1):pre-selection 779820 0.79

(2) : (1) + volume cut

1224 1.2e-3

(3) : (2) + timing cut

180 1.8e-4

(4) : (3)+ band cut 1 1.0e-6

Reconstructed R

# o

f eve

nts

Signal region

23

Origin of BG in XMASS-I

2424

Al seal

Main BG source ( 5keV)≧

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