Status of XMASS experiment Cygnus 2013Toyama 20130605 Nagoya

Status of XMASS experiment Cygnus 2013@Toyama 2013/06/05 Nagoya univ. H. Uchida for XMASS collaboration 1

XMASS‐I Overview XMASS‐ 1. 5 835 kg, 5 ton, 1 ton FV 100 kg Fiducial volume (FV) φ1. 5 m, ~1000 PMTs φ80 cm, 642 PMTs ・ Dark matter search XMASS‐II 25 ton, 10 ton FV φ2. 5 m 　・ Dark matter 　・ pp solar neutrino 　・ 0 n 2 b decay Y. Suzuki, hep-ph/0008296 • 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 0ν 2β decay. 2

800 kg 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 (~14 p. e. /ke. V) & low energy threshold (~0. 3 ke. Vee). • This detector is sensitive for electromagnetic signals. 3

Detector configuration There is a this detector at Kamioka observatory. Elec. hut OFHC copper vessel Water tank Refrigerator 11 m 835 kg liq. xenon 10 m 700 L reservoir 72 20 inch PMTs (veto) ~ 1. 2 m 642 PMTs 4

Source calibration • Calibration sources are used for checking detector response. • The sources can be moved along the vertical axis in the detector. RI Energy [ke. V] (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 Stepping motor [Hz] dia. [mm] Linear and rotary motion feed-through (*1) Ka X‐rays from the copper used for housing. (*2) Ka X‐rays from the tungsten used for housing. Gate valve ~5 m 0. 21 mmf for 57 Co source 4 mmf Source rod with a dummy source Top photo tube • 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. 5 5

Calibration data 57 Co Real data 40 30 20 ４ 10 ０ ３ 0 ０ ‐ 10 z [cm] • Calibration dataでreal dataを calibration data (122 ke. V) MC 40 30 20 10 0 ‐ 10 ‐ 20 ‐ 30 ‐ 40 ‐ 20‐ 10 0 10 20 y [cm] 6

Background dru [/day/ke. Vee/kg] • Background level of XMASS‐I is a few event/day/ke. V/kg [dru] without fiducualization. • It is similar level with DAMA and Co. Ge. NT. • The origin of BG for more than 5 ke. V were almost identified (lower figure). Also for less than 5 ke. V, Gore‐ Tex may explain the events. • Events originate at the inner surface must explain major part of the observed events. . Full volume 5 10 PMT写真と アルミの位置の 説明 15 20 ● Black line: Real data ● Colored histogram: BG (MC) Surface Cu 210 Pb PMT Al 235 U-231 Pa 210 Pb 232 Th 238 U-230 Th PMT gamma Gore-Tex 210 Pb Gore-Tex 14 C 7 7

Light mass WIMP search Counts/day/kg/ke. Vee l Full volume (835 kg) analysis l 6. 70 days× 835 kg in 2012 Feb. l 0. 3 ke. Vee threshold 5 4 3 2 1 0 0 0. 5 1 1. 5 Energy [ke. Vee] 2 8

solar axion search l Axion is a hypothetical particle to solve the strong CP problem l Produced in the Sun and detected in the detector l XMASS is suitable to search because of a large mass and low BG Bremsstrahlung and Compton effect Axio-electric effect gaee ma = Our data Max allowed 50 ke. V 9

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

Event/ke. V Cross section of DM 100 Ge. V Scaled energy(13. 9 PE/ke. V) # of events of no cut in DM 100 Ge. V MC are 82625. If these events occur in 55. 6 days, Calculation of cross section NA of Xe 129 DM 100 Ge. V: 82625/835/0. 264/55. 6 = 6. 74 event/kg(Xe 129)/day Reconstructed R (cm) (explanation of this function in backup slide) = 3. 758× 10‐ 37 × 6. 74× 100/0. 3 = 8. 4× 10‐ 34 cm 2 (8. 4× 102 pb) When cross section is 8. 4× 102 pb, inelastic events by DM 100 Ge. V occur 82625 events in 55. 6 days. 19

Event/ke. V Cross section of DM 200 Ge. V Scaled energy(13. 9 PE/ke. V) # of events of no cut in DM 200 Ge. V MC are 82640. If these events occur in 55. 6 days, Calculation of cross section NA of Xe 129 DM 200 Ge. V: 82640/835/0. 264/55. 6 = 6. 74 event/kg(Xe 129)/day Reconstructed R (cm) (explanation of this function in backup slide) = 3. 758× 10‐ 37 × 6. 74× 200/0. 5 = 1. 0× 10‐ 33 cm 2 (1. 0× 103 pb) When cross section is 1. 0× 103 pb, inelastic events by DM 200 Ge. V occur 82640 events in 55. 6 days. 20

Event/ke. V Cross section of DM 400 Ge. V Scaled energy(13. 9 PE/ke. V) # of events of no cut in DM 400 Ge. V MC are 82175. If these events occur in 55. 6 days, Calculation of cross section NA of Xe 129 DM 200 Ge. V: 82175/835/0. 264/55. 6 = 6. 70 event/kg(Xe 129)/day Reconstructed R (cm) (explanation of this function in backup slide) = 3. 758× 10‐ 37 × 6. 70× 400/0. 53 = 1. 9× 10‐ 33 cm 2 (1. 9× 103 pb) When cross section is 1. 9× 103 pb, inelastic events by DM 400 Ge. V occur 82175 events in 55. 6 days. 21

reductio n No cut 2094840 1 (1): pre‐selection 1651610 0. 79 (2) : (1) + volume cut 2877 1. 4 e‐ 3 (3) : (2) + timing 417 cut Signal region 2. 0 e‐ 4 (4) : (3)+cut band cut # 7 of events (3065 ke. V) reductio 3. 3 e‐ 6 n No cut 990692 1 (1): pre‐selection 779820 0. 79 (2) : (1) + volume cut 1224 1. 2 e‐ 3 # of events (20100 ke. V) cut Live time: 55 days Energy(ke. V) # of events Reduction of best parameter set 22 Reconstructed R

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Origin of BG in XMASS-I Main BG source (≧ 5 ke. V) Al seal BG candidate (< 5 ke. V) l In refurbishment, Al seal will be covered by copper rings and GORE-TEX will be removed l In XMASS-1. 5, Al seal will be replaced 24 with ultra pure one