XMASS 15: The Next Step in Kamioka, Japan Benda Xu on behalf of XMASS collaboration XIV International Conference on Topics in Astroparticle and Underground Physics Torino, Italy September 10, 2015 Benda Xu (IPMU) XMASS 15: The Next Step in Kamioka, Japan September 10, 2015 1 / 23
XMASS XMASS Project: Multi-Purpose Liquid Xenon Detectors Xenon MASSive detector for solar neutrino (pp/ 7 Be) Xenon neutrino MASSdetector (0νββ of 136 Xe) Xenon detector for Weakly Interacting MASSive Particles XMASS-I: 01/08 t * XMASS-15: 1/5 t XMASS-II: 10/25 t Running Material Screening, Design Ultimate * In terms of ducial/total mass Y Suzuki (2000) Low Energy Solar Neutrino Detection by using Liquid Xenon arxiv: hep-ph/0008296 Benda Xu (IPMU) XMASS 15: The Next Step in Kamioka, Japan September 10, 2015 2 / 23
XMASS XMASS Site and Detector Structure The outer water Cherenkov detector will be reused in XMASS-15 Japan Kamioka Mine Tokyo K Abe et al (2013) XMASS detector Benda Xu (IPMU) NIM A 716 00013, pp 78 85 XMASS 15: The Next Step in Kamioka, Japan September 10, 2015 3 / 23
XMASS Detector Response Liquid Xenon scintillation: 14 PE/keV Event reconstruction based on detector simulation Position resolution (RMS): 14 cm @ z = 0 cm 10 cm @ z = ±20 cm Calibration Sources Source Energy (kev) Hz 55 Fe 59 5 109 Cd 8, 22, 25, 88 800 241 Am 178, 595 500 57 Co 593, 122 30 137 Cs 662 200 Arbitrary unit Arbitrary unit Data MC 593 kev (W) Data MC z [cm] 122 kev RMS ~4% 136 kev Reconstructed energy [kev] Benda Xu (IPMU) XMASS 15: The Next Step in Kamioka, Japan September 10, 2015 4 / 23
XMASS Physics Results Light WIMP search, Phys Lett B 719 (2013) 78 Solar axion search, Phys Lett B 724 (2013) 46 Bosonic Super-WIMPs, Phys Rev Lett 113 (2014) 121301 Inelastic scattering on 129 Xe, PTEP 2014, 063C01 To be published: Seasonal modulation with full volume Tuesday Parallel Session Dark Matter A by Kazuyoshi Kobayashi 124 Xe double electron capture Monday Parallel Session Neutrinos B by Katsuki Hiraide Nearby supernova ν detection Fiducial volume analysis for heavy WIMPs Benda Xu (IPMU) XMASS 15: The Next Step in Kamioka, Japan September 10, 2015 5 / 23
XMASS Physics Results Xe10-S2 LUX DAMA/LIBRA (2009 Savage) XMASS2013 CDMS-Si CoGent ML (2014) XENON100 XMASS ± 1 σ expected ± 2 σ expected Leff uncertainty is taken into account Figure is drawn by Method 1 The difference between two methods are within 30% DAMA/LIBRA region is mostly excluded by our measurement Model assumption V 0 : 2200 km/s V esc : 6500 km/s ρdm: 03 GeV/cm 3 Lewin, Smith (1996) Ÿ K Kobayashi's talk for XMASS Collaboration at this conference, seasonal modulation Benda Xu (IPMU) XMASS 15: The Next Step in Kamioka, Japan September 10, 2015 6 / 23
XMASS Backgrounds Background from Liquid Xenon: 85 Kr (<27 ppt) is removed with distillation system 222 Rn (82(5) mbq) is monitored World s lowest Rn concentration in Xe Rn daughters (esp 210 Pb) on detector surface: use radiochemically pure copper after electropolishing to cover them γ ray from PMT parts To be reduced further Benda Xu (IPMU) XMASS 15: The Next Step in Kamioka, Japan September 10, 2015 7 / 23
XMASS-15 XMASS 15: The Next Step, Bigger and Cleaner Scale up XMASS-I 01 t ducial mass Ö 10 = 1 t Single-phased liquid Xenon is relatively easy to scale up the bigger, the better Deal with background Screen materials for PMT production Targeting 1 10 6 dru background contribution 1 radioactivity 10 reduction in Next generation PMT to detect and reject surface radiation more eectively Dierential rate unit, dru:=/kev/kg/day ν coherent scattering is 1 10 5 dru Benda Xu (IPMU) XMASS 15: The Next Step in Kamioka, Japan September 10, 2015 8 / 23
XMASS-15 XMASS 15: Expected Sensitivity Joining the race XMASS-15 line features 1 year's data with 1 10 5 dru background Benda Xu (IPMU) XMASS 15: The Next Step in Kamioka, Japan September 10, 2015 9 / 23
XMASS-15 XMASS 15: Intercept Light from Detector Surface Catch more photons from the innner surface Identify and reject events originating from radio-isotope on the surface and PMT Red arrows: track of scintillation photons small curvature photo cathode PMTs for XMASS-I miss many photons from the surface large curvature photo cathode PMTs for XMASS-15 can detect photons from the surface Concept: Ability to catch photon from the side of PMT Benda Xu (IPMU) XMASS 15: The Next Step in Kamioka, JapanSeptember 10, 2015 10 / 23
New PMT R13111 R13111 Features (comparison to R10789) R10789 R13111 Developped for XMASS-I XMASS-15 Diameter (inch) 2 3 Photocathod Shape at dome Radioactivity 1 1/10 Transition Time Spread(FWHM ns) 6 3 Al Seal - reduced Th and U Length - shortened Easier for PMT holder design Benda Xu (IPMU) XMASS 15: The Next Step in Kamioka, JapanSeptember 10, 2015 11 / 23
New PMT R13111 Experimental Setup and Single Photoelectron Gain Photocathod has a large solid view angle of 2π Sensitivity at the side is important for rejecting surface events Layer 0 2nd dynode 1st dynode Layers 1 to 3 (from bottom) 0 145mm 95mm 45mm 2nd dynode 1st dynode 30 Layer 1,2,3 can rotate with the cap Layer 0 is a reduced layer that represents the top of photocathod Benda Xu (IPMU) XMASS 15: The Next Step in Kamioka, JapanSeptember 10, 2015 12 / 23
New PMT R13111 Experimental Setup and Single Photoelectron Gain Photocathod has a large solid view angle of 2π Sensitivity at the side is important for rejecting surface events Benda Xu (IPMU) XMASS 15: The Next Step in Kamioka, JapanSeptember 10, 2015 12 / 23
New PMT R13111 Experimental Setup and Single Photoelectron Gain Photocathod has a large solid view angle of 2π Sensitivity at the side is important for rejecting surface events 095 100 105 0 60 120 180 240 300 Degree Gain normalized to photocathod top layer 0 1 2 3 Benda Xu (IPMU) XMASS 15: The Next Step in Kamioka, JapanSeptember 10, 2015 12 / 23
New PMT R13111 Photocathod: Sensitivity from the Sides Charge normalized photocathod top 14 13 12 11 10 09 0 60 120 180 240 300 Degree layer 0 1 2 3 Eectiveness of detecting transverse light is conrmed Expected variation is observed Benda Xu (IPMU) XMASS 15: The Next Step in Kamioka, JapanSeptember 10, 2015 13 / 23
New PMT R13111 Relative Collection and Quantum Eciencies f e Benda Xu (IPMU) XMASS 15: The Next Step in Kamioka, JapanSeptember 10, 2015 14 / 23
New PMT R13111 Cyrogenic Performance and Material Screening The PMTs were conrmed to be stable (similar to present and previous PMTs used) in liquid Xe underground for 1 month: no discharge found Cooling chamber with liquid N 2 Gain dependence on temperature and relaxation are observed Dark rates decrease at low temperature PMT parts (except photocathod) before assembly are counted underground with HPGe Detectors Table: Units are mbq U chain Th chain 60 Co 40 K Present PMT 076(24) 12(3) 29(2) 01(22) PMT raw material screening are carried out jointly by XMASS collaboration and Hamamatsu Photonics Inc Benda Xu (IPMU) XMASS 15: The Next Step in Kamioka, JapanSeptember 10, 2015 15 / 23
Epilogue Summary XMASS-15 is the next step of the running XMASS-I, scaling up 10 times ducial mass up to 1 t Measures to counteract background have been developed to reect our best knowledge with the running detector The central technique is the new PMT R13111 with dome-shaped photocathod to detector surface radioactivity First batchs of R13111 are tested in the laboratory Further material screen and mass production is under discussion Benda Xu (IPMU) XMASS 15: The Next Step in Kamioka, JapanSeptember 10, 2015 16 / 23
Epilogue XMASS Collaboration 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, B Yang Kavli IPMU, the University of Tokyo: JLiu, KMartens, Y Suzuki, Benda Xu Kobe University: R Fujita, K Hosokawa, K Miuchi, Y Ohnishi, N Oka, 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, H Takiya Tokushima University: KFushimi Sejong University: N Y Kim, Y D Kim KRISS: Y H Kim, M K Lee, K B Lee, J S Lee Benda Xu (IPMU) XMASS 15: The Next Step in Kamioka, JapanSeptember 10, 2015 17 / 23
Backup Refurbishment Refurbishment of Detector In commissioning run, we found background source PMT s Al seal (210Pb, 238U) Al seal placed area is the one of the most difficult area to look from that PMT Al makes shadow These makes leakage event, misidentified as center region events To reduce this background and confirm our understanding of BG As refurbishment, we put new structure to cover completely this Al seal After RFB Shadow region Al seal Before RFB High purity Al is vapored pe yield 139 kev Al seal Benda Xu (IPMU) XMASS 15: The Next Step in Kamioka, JapanSeptember 10, 2015 18 / 23
Backup Transit Time Dependence on Photocathod Incident Postion 60 120 180 240 300 0/360 268 269 270 271 272 Degree Time (ns) layer 0 1 2 3 Transit Time Uniformity of PMT ZK7340P Benda Xu (IPMU) XMASS 15: The Next Step in Kamioka, JapanSeptember 10, 2015 19 / 23
Backup Relative Gain Variation Among PMTs 10 11 ZK7323ZK7324PZK7325PZK7328PZK7333PZK7334PZK7335ZK7339PZK7340ZK7340PZK7341PZK7348ZK7349P PMT serial No Gain normalized to layer 0 PMT Gain Comparison Benda Xu (IPMU) XMASS 15: The Next Step in Kamioka, JapanSeptember 10, 2015 20 / 23
Backup Moon Chamber Setup Moon chamber Setup Source position is off-center LED Am241 Benda Xu (IPMU) XMASS 15: The Next Step in Kamioka, JapanSeptember 10, 2015 21 / 23
Backup LN2 Setup Benda Xu (IPMU) XMASS 15: The Next Step in Kamioka, JapanSeptember 10, 2015 22 / 23
Backup L eff of XMASS Energy threshold: 03 kevee Benda Xu (IPMU) XMASS 15: The Next Step in Kamioka, JapanSeptember 10, 2015 23 / 23