Status of XMASS experiment Shigetaka Moriyama Institute for

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

Y. Suzuki, hep-ph/0008296 XMASS project Multi purpose low-background experiment with liq. Xe l Xenon MASSive detector for solar neutrino (pp/7 Be) l Xenon neutrino MASS detector (bb decay) l Xenon detector for Weakly Interacting MASSive Particles (DM search) XMASS-II XMASS-1. 5 XMASS-I x 10 FM Phase I: 0. 1 t fiducial mass (Total 835 kg) 1 t FM (total 5 t) 2015 - Final goal: 10 t fiducial Mass (total 25 t) 2020 -

XMASS-I detector construction

Demonstration of the detector performance 57 Co W X ray 122 ke. V 4%rms Reconstructed Position distribution Real Data Simulation 60 ke. V • The detector gave high photoelectron yield ~14. 7 p. e. /ke. V Largest among DM detectors. • Vertex recon. by pattern of p. e. • Detailed description of the detector: NIMA 716 (2013) 78 4

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 129 Xe • Vector boson super-WIMPs (NEW!) Results to be shown soon • Seasonal modulation with 835 kg LXe • Fidicual volume cut analysis (heavy WIMPs)

Light WIMP search Phys. Lett. B 719 (2013) 78 • All the volume (835 kg of LXe w/o fiducialization), >=4 hits. • Large p. e. yield, 14. 7 p. e. /ke. V, thre. confirmed by LED’s data low Energy threshold 300 e. Vee was achieved. • Simple cut to remove Cherenkov events was used. DAMA XMASS XENON 10 EDELWEISS CDMSII-Ge XENON 100

Solar axion search Phys. Lett. B 724 (2013) 46 • 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 <40 ke. V Out data Maximum allowed

Inelastic scattering • WIMPs would cause inelastic scattering on 129 Xe. Nuclear recoil as well as 40 ke. V g ray emission are expected. Peak search @40 ke. V. • 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 -50 ke. V) R<15 cm 22% efficiency For 100 Ge. V

Vector super-WIMPs • CDM has problems on galactic scales. Lighter DM (ke. VMe. V) gives better understanding. Detectable by photoelectric effect. Similar cuts as inelastic study were used. • The 1 st exp. result to constrain DM in 40 -80 ke. V. (>80 ke. V soon) Real data (82. 7 d) After R, timing, and band cut Ge detector y r a in m i l e pr m. V=80 ke. V simulated signal Efficiency 80% in R<16 cm M. Pospelov et al. , PRD 78, 115012 (2008) J. Redondo M. Postma JCAP 02 (2009)005

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 XMASS 1. 5. Aluminum Events/day/ke. V/kg simulation reduction w/o cover w/ cover [cpd] Reduction of 210 Po by EP 105 <0. 3% <0. 6% 0. 3+/-0. 5% 104 103 102 101 1 A　　　　 B　 　C [Bq] Reduction of 210 Pb by EP 2 ~1/10 must be achieved Energy (ke. V) 1 0 0 A　 　　　B　 　　　 C

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.

XMASS-1. 5 • 5 ton of liquid xenon (1 ton 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-I High probability to miss catching the photons from the surface. PMTs for XMASS-1. 5 Scintillation light from the surface can be detected.

Impact on BG reduction • MC simulation with convex-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. XMASS-I some PMTs not shown XMASS-1. 5 Dome shape PMTs Performance of BG rejection for surface BG is under study.

Sensitivity of XMASS-1. 5 • Heavy WIMPs will be searched for using fidicial cut analyses. – s. SI<10 -46 cm 2 • Light WIMPs will be searched for at low energy of all volume data. – s. SI~a few x 10 -42 cm 2 • ~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 (2 ke. V energy threshold, 1 yr exposure)

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 s. SI~10 -46 cm 2 in 1 yr exposure.