Cygnus 2013/06/05 Nagoya univ. H.Uchida for XMASS collaboration 1

Overview kg, 100 kg Fiducial volume (FV) φ80 cm, 642 PMTs XMASS-II 25 ton, 10 ton FV φ2.5 m ・ Dark matter ・ pp solar neutrino ・  decay XMASS ton,1 ton FV φ1.5 m, ~1000 PMTs 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 and May And now refurbishment work is on going. XMASS-II has multi purpose of dark matter, pp solar neutrino and 0ν2β decay. Y. Suzuki, hep-ph/

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 ~ 1.2m 642 PMTs OFHC copper vessel 835kg liq. xenon Water tank Refrigerator 72 20inch PMTs (veto) Elec. hut 4 700L reservoir There is a this detector at Kamioka observatory.

Source calibration 5 Stepping motor Linear and rotary motion feed-through Top photo tube ~5m Gate valve 5 4mm  0.21mm  for 57 Co source Source rod with a dummy source RIEnergy [keV][Hz]dia.[mm] (1) Fe (2) Cd-1098(*1), 22, 25, (3) Am , (4) Co (*2), (5) Cs (*1) K  X-rays from the copper used for housing. (*2) K  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 dataMC 57 Co calibration data (122keV) ４０３０４０３０ 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 Full volume dru [/day/keVee/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) analysis 6.70 days×835kg in 2012 Feb. 0.3 keVee threshold Energy [keVee] Counts/day/kg/keVee

solar axion search 9 Our data ma=ma= 50 keV Max allowed Axion is a hypothetical particle to solve the strong CP problem Produced in the Sun and detected in the detector XMASS is suitable to search because of a large mass and low BG Bremsstrahlung and Compton effect g aee 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 = 3.758× ×6.74×100/0.3 = 8.4×10 ‐34 cm 2 (8.4×10 2 pb) (explanation of this function in backup slide) NA of Xe129 # of events of no cut in DM100GeV MC are If these events occur in 55.6days, Calculation of cross section DM100GeV: 82625/835/0.264/55.6 = 6.74 event/kg(Xe129)/day Scaled energy(13.9PE/keV) Event/keV When cross section is 8.4×10 2 pb, inelastic events by DM100GeV occur events in 55.6days. Event Reconstructed R (cm)

Cross section of DM200GeV 20 = 3.758× ×6.74×200/0.5 = 1.0×10 ‐33 cm 2 (1.0×10 3 pb) (explanation of this function in backup slide) NA of Xe129 # of events of no cut in DM200GeV MC are If these events occur in 55.6days, Calculation of cross section DM200GeV: 82640/835/0.264/55.6 = 6.74 event/kg(Xe129)/day When cross section is 1.0×10 3 pb, inelastic events by DM200GeV occur events in 55.6days. Scaled energy(13.9PE/keV) Event/keV Event Reconstructed R (cm)

Cross section of DM400GeV 21 = 3.758× ×6.70×400/0.53 = 1.9×10 ‐33 cm 2 (1.9×10 3 pb) (explanation of this function in backup slide) NA of Xe129 # of events of no cut in DM400GeV MC are If these events occur in 55.6days, Calculation of cross section DM200GeV: 82175/835/0.264/55.6 = 6.70 event/kg(Xe129)/day When cross section is 1.9×10 3 pb, inelastic events by DM400GeV occur events in 55.6days. Scaled energy(13.9PE/keV) Event/keV Event Reconstructed R (cm)

Reduction of best parameter set 22 Energy(keV) # of events Live time: 55 days cut# of events ( keV) reductio n No cut (1):pre-selection (2) : (1) + volume cut e-3 (3) : (2) + timing cut e-4 (4) : (3)+ band cut73.3e-6 cut# of events (30- 65keV) reductio n No cut (1):pre-selection (2) : (1) + volume cut e-3 (3) : (2) + timing cut e-4 (4) : (3)+ band cut11.0e-6 Reconstructed R # of events Signal region

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Origin of BG in XMASS-I 24 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