Status of XMASS experiment

1. Status of XMASS experiment Shigetaka Moriyama Institute for Cosmic Ray Research, University of Tokyo For the XMASS collaboration September 10th, 2013 @ TAUP2013 Asilomar

2. Y. Suzuki, hep-ph/0008296 XMASS project Multi purpose low-background experiment with liq. Xe • Xenon MASSive detector for solar neutrino (pp/7Be) • Xenon neutrino MASS detector (bb decay) • Xenon detector for Weakly Interacting MASSive Particles (DM search) XMASS-II XMASS-1.5 XMASS-I x10 FM x10 FM 1t FM (total 5t) 2015- Final goal:10t fiducial Mass (total 25t) Phase I: 0.1tfiducial mass (Total 835kg) 2020-

3. XMASS-Idetectorconstruction

4. Demonstration of the detector performance Reconstructed Position distribution • The detector gave high photo-electron yield ~14.7p.e./keVLargest among DM detectors. • Vertex recon. by patternof p.e. • Detailed description of the detector: NIMA 716 (2013) 78 57Co 122keV 4%rms Real Data Simulation W X ray 60keV

5. Physics results of XMASS-I Published results (low threshold & low BG, no reconst.) • Light WIMP search, Phys. Lett. B 719 (2013) 78 • Solar axion search, Phys. Lett. B 724 (2013) 46 Recent progress (low background in deep inside) • Inelastic scattering on 129Xe • Vector boson super-WIMPs (NEW!) Results to be shown soon • Seasonal modulation with 835kg LXe • Fidicual volume cut analysis (heavy WIMPs)

6. Phys. Lett. B 719 (2013) 78 Light WIMP search • All the volume (835kg of LXe w/o fiducialization), >=4hits. • Large p.e. yield, 14.7p.e./keV,thre. confirmed by LED’s data  low Energy threshold 300eVee was achieved. • Simple cut to remove Cherenkov events was used. DAMA XMASS XENON10 EDELWEISS CDMSII-Ge XENON100

7. Phys. Lett. B 724 (2013) 46 Solar axion search • Same data set as the light WIMPs search • Generated in the Sun by bremsstrahlung and Compton effect, observed by axio-electric effect in XMASS. • Strong experimental constraint <40keV Out data Maximum allowed

8. Inelastic scattering • WIMPs would cause inelastic scattering on 129Xe. Nuclear recoil as well as 40keV g ray emission are expected.Peak search @40keV. • Various cuts are used (reconstructed radius cut, timing cut, and pattern cut “band cut”) • Another way for study on SD interaction. No event in signal window (37-50keV) R<15cm 22% efficiency For 100GeV

9. Vector super-WIMPs • CDM has problems on galactic scales. Lighter DM (keV-MeV) gives better understanding. Detectable by photo-electric effect. Similar cuts as inelastic study were used. • The 1st exp. result to constrain DM in 40-80keV. (>80keV soon) Real data (82.7d) After R, timing, and band cut Ge detector M. Pospelov et al., PRD 78, 115012 (2008) preliminary mV=80keV simulated signal Efficiency 80% in R<16cm J. Redondo M. Postma JCAP02 (2009)005

10. Refurbishment of XMASS-I • Most of BG is caused by low energy b from Al seal of PMTs. • ~1/10 of the background: radon daughters on the surface. • Confirmation/establishing surface treatment for XMASS1.5. Aluminum simulation w/o cover [cpd] 105 104 103 102 101 1 [Bq] reduction w/ cover 0.3+/-0.5% <0.3% <0.6% Reduction of 210Pb by EP 2 Events/day/keV/kg 1 ~1/10 must be achieved Energy (keV) 0 0 ABC ABC

11. Status of refurbishment work • We are almost finishing the refurbishment work. • In this week the detector will be hung up to the original place and chambers will be set. • Data taking will be resumed in this fall.

12. XMASS-1.5 • 5ton of liquid xenon (1ton of fiducial mass) • Background reduction • No dirty aluminum, no suspicious GORETEX • Finite amount of surface BG must be assumed. • Round shape PMTs for robust identification of surface BG. Red arrows: track of scintillation photons Dotted line = photo cathode Dotted curve = photo cathode PMTs for XMASS-1.5 Scintillation light from the surface can be detected. PMTs for XMASS-I High probability to misscatching the photons from the surface.

13. Impact on BG reduction • MC simulation withconvex-concave PMTs. • Photons caused by an event happening in between PMTs can be caught by 40-48% prob. by adjacent three PMTs. • Easier/robust identification of surface background. • Optimization of PMT shape is ongoing. Performance of BG rejection for surface BG is under study. XMASS-I some PMTs not shown XMASS-1.5 Dome shape PMTs

14. Sensitivity of XMASS-1.5 • Heavy WIMPs will be searched for using fidicial cut analyses. • sSI<10-46cm2 • Light WIMPs will be searched for at low energy of all volume data. • sSI~a few x 10-42cm2 • ~2 orders of magnitude better for ALPs. • Prototype of XMASS-II. • Plan to start in 2015. Analysis with low energy events Analysis with fiducial cuts(2keV energy threshold, 1yr exposure)

15. Summary • XMASS-I has high light yield and low threshold. Physics results as demonstration of its performance. • Light WIMPs, solar axion, inelastic scattering, and vector bosons. • Seasonal modulation and fiducial volume analysis will come soon. • Refurbishment work for confirmation of BG and establishment of surface treatment is ongoing. • Data taking will resume in this fall. Seasonal modulation, etc. • XMASS-1.5 is planned to start in 2015. It has a sensitivity sSI~10-46cm2 in 1yr exposure.