XMASS. 12/07/25 Y. in Chicago 1

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1 XMASS Y. Suzuki Kamioka Observatory, Ins;tute for Cosmic Ray Research ICRR), University of Tokyo And Kamioka Satellite, Kavli Ins;tute for the Physics and Mathema;cs of the Universe (IPMU), University of Tokyo 12/07/25 Y. in Chicago 1

2 Physics Objec;ves of XMASS Mul;- purpose liq. Xenon detector Final Goal: 10 ton fiducial mass, 25 ton total(2.5mφ) pp- solar neutrinos: ν+e à ν+e Double beta decay 136 Xe à 136 Ba + 2e - Dark Ma[er: χ+xe à χ+xe Y. Suzuki, hep- ph/ è Phase- I (100 kg fid.): dedicated to a search for WIMPs dark ma[er Search down to σ SI a few x cm 2 BG level in the fiducial volume: 10-4 /kg/kev/day 12/07/25 Y. in Chicago 2

3 The phase- I XMASS detector Detector Single phase (scin;lla;on only) liquid Xenon detector 100 kg fid. mass, [835 kg inner mass (0.8 mφ)] 630 hexagonal & 12 round PMTs with 28-39% Q.E. photocathode coverage: > 62% inner surface: : 14.7±1.2 pe/kev Can achieve low energy threshold Sensi;ve also to electron/γ events 1.2m diameter 12/07/25 Y. in Chicago 3

4 Detector Construc;on : PMT holder and PMT installa;on : Construc;on Completed 12/07/25 Y. in Chicago 4

5 Commissioning run Source rod RI OFHC Calibra;on Source Rod (57Co, 241Am, 137Cs, 109Cd, 55Fe) External sources: 60Co, 137Cs, 232Th, Neutron Normal Data taking (physics runs) Development of Sonware Change of the physical condi;on of Xenon. High/Low pressure runs, O2 runs to change absorp;on length, etc. Top PMT Removal Mechan. Xenon gas Winder Gate valve 5m Xe Gas run Important to iden;fy the BG RI measurement of the detector parts(a[ach materials at the end of the calibra;on rod) CM runs ended because the calibra;on rod fell off and stuck 12/07/25 Y. in Chicago 5 Top PMT

6 Energy and vertex reconstrucgon For 57 Co (122keV, γ- rays) Energy resolu;on: 4% rms High p.e. yield: 14.7±1.2 pe/kev Posi;on Resolu;on: 1.4 cm rms (0cm: center) 1 cm rms (±20cm) 12/07/25 Y. in Chicago 6

7 Measured Spectrum (Whole Volume) ~1MeV ~50keV Observed data MC: PMT γ rays We an;cipated that the most backgrounds come from PMT γ (measured by Ge detector) (shown by yellow) But we found unexpected BG which dominates below kev. In the signal region below 10keVee, it amounts 2 order of magnitude larger than PMT BG 12/07/25 Y. in Chicago 7

8 Measured Spectrum (Whole Volume) ~1MeV Observed data MC: PMT γ rays MC: PMT Al 238U & Pb210 Suspected detector parts were examined again, and found Aluminum seal used between quarts window and metal body of the PMTs contains 238 U (upper chain) and 210 Pb 210 Pb on Cu surface (as usual) ~50keV Aluminum Seal 12/07/25 Y. in Chicago 8

9 ~5keV ~5keV Measured BG Spectrum below (5Whole kev Volume) MC: GORE- TEX Modern C: 7.5% 0.3mm a[. Inside GORE- TEX MC: GORE- TEX Modern C: 7.5% 0.3mm a[. Inside GORE- TEX m = 30GeV mdm DM = 18 GeV - 41cm2 2 σ = 1.4x10-41 σsi SI = 1.6x10 cm 12/07/25 BG below 5 kev: not explained by Al- seal and surface 210Pb GORE- TEX GORE- TEX: between PMT and holder used for a light seal contains up to 6±3% of modern carbon GORE- TEX might explain But parameters ( ex. transparency of light inside of GORE- TEX) are not well known There may be uniden;fied sources of BG or something else. We will remove GORE- TEX in future detector refurbishment Y. in Chicago 9

10 Internal BG 222 Rn: 214 Bi à 214 Po(164µs) à 210 Pb 8.2±0.5mBq in the en;re inner volume (835kg) 220 Rn: 220 Rn à 216 Po(0.14s) à 212 Pb Upper limit <0.28mBq (90%C.L.) 1 st event ( 214 Bi β) 2 nd event ( 214 Po α) Tail due to satura;on Fiung with an expected decay curve current(pa) API- MS Time difference (µs) Kr: by API- MS Kr < 2.7ppt 85 Kr goal: 2ppt 12/07/25 Y. in Chicago 10

11 Background level Our BG level (whole volume) aner removing Cherenkov events is s;ll low even with the unexpected surface backgrounds. E. Aprile, 2010 Princeton Evens/kg/day/keV XMASS full volume 12/07/25 Y. in Chicago 11

12 Physics analysis Analysis with different volumes and thresholds Whole Volume Analysis (Large target mass of 835 kg, low energy threshold, (large BG), no reconstruc;on) 1) lowest threshold analysis (> 0.3 kevee) (Low mass DM search) 2) 2keVee threshold annual modula;on (e/γ/nr) 3) kev Axion DM (ex. super- WIMPs) (e/γ) 4) Solar Axions (e/γ) è Light WIMPs &ALP Latest status w/o XMASS XENON100, July 18, Fiducial Volume analysis (low BG) 1) Standard WIMPs search (> 2 5 kev) 12/07/25 Event reconstruc;on/reduc;on program Y. in Chicago 12

13 Whole Volume Analysis with lowest threshold We took data with 4 hits threshold and analyze the events above > 0.3 kevee for en;re volume Trigger efficiency For 7 GeV DM kev > kev Raw data Clean up + Cherenkov Cuts 0.3 kev 6.64 days in Feb Clean up Cut: Cherenkov rejec;on 1 (# of hits in 20ns window)/(total # of hits) > 0.6 Scin;lla;on: 0.5, Cherenkov: K decay in photo cathodes to create Cherenkov in the window of PMT 12/07/25 Most BG in this energy region Y. in Chicago 13

14 6.64 days x 835 kg (5546 kg*days) 7 GeV, 4.76x10-40 cm 2 12 GeV, 3.05x10-41 cm 2 18 GeV, 1.57x10-41 cm 2 Results on low mass dark ma[er XMASS: stat.+syst. (90% lower bound) Leff uncertainty band Compare Dark Ma[er MC to the data Obtain the maximum cross sec;on (upper limits) of the spectrum not to exceed the observed data points. Current XMASS is close to the allowed regions of DAMA/CoGeNT/ CRESST. We will reduce the backgrounds in near future 12/07/25 Y. in Chicago 14

15 Annual modula;on (Sensi;vity test) Use all the available data from commissioning runs: 165 days; divided into 11 periods Same event reduc;on for low energy whole volume analysis Energy scale based on 57Co data (±3%) Scale factor re- adjustment by 60Co in each periods ( %) Count number of events Check for 2-6 kevee DAMA modula;on Good test for electron/γ events (ex. Luminous DM) [not a test for NR] χ for flat 31.6 for DAMA modula;on 2 6 kevee Parameters: A= /kev/kg/day T=365 days, peak=159.2 days 12/07/25 Y. in Chicago 15

16 Nuclear Recoil Test for Nuclear Recoil: QF(Na) 0.25, Leff(Xe) keVee(Na) è 8 24 kev NR è 1 4keVee(Xe) but 1/30 sensi;vity ç recoil shape, A 2 dependence,. Current XMASS does not have a sensi;vity χ 2 : 10.8 for flat, 23.8 for the DAMA modula;on 1-4 kevee(xe) ó 2-6 kevee (Na) 2 6 kevee (I) è kev kevee(xe): under study 12/07/25 Y. in Chicago 16

17 DM Axions Event Rate for the axion dark ma[er (through axio- electric effect) g aee : strength of the coupling constant, m a : axion mass in kev, σ pe : photo- electric cross sec;on in barns/atom Ge Xe M edge Ge L edge Xe Obtain absolute rate limits Observed spectrum g aee = 1X10-10 Expected spectrum for m a =3keV 12/07/25 Y. in Chicago 17

18 DM Axions Results show that XMASS have similar sensi;vity to the current experiments. The fiung the signal with backgrounds above 5 kev, where we know the background very well, will increase the sensi;vity by factor of 5 (in future) g aee DAMA allowed XMASS CoGeNT 2011 CDMS 2009 Preliminary XMASS fiung result > 5 kev (sensi;vity study) 12/07/25 Y. in Chicago 18

19 Solar Axions Produc;on: Various mechanism 1. Bremsstrahlung and Compton sca[ering (g aee ) e g aee e a 2. Primakoff effect (g aγγ ) 3. Nuclear de- excita;on (57Fe) (g an ) Line kev γ g aγγ γ x a Observa;on through axio electric effect (g aee ) 12/07/25 Y. in Chicago 19

20 Solar Axions Bremsstrahlung and Compton scattering (g aee ) Limits from absolute maximum: g aee = 4.5x10-11 Allowed mass for par;cular models: < 200 ev for KSVZ < 2 ev for DFSZ Data XMASS 4.5x10-11 Derbin CoGeNT Axion signal (MC) g aee = 4.5x10-11 Solar limit 2.8 X10-11 XMASS By DM Axion CDMS 12/07/25 Y. in Chicago 20

21 Solar Axions Primakoff: gaγγ & gaee Black body spectrum with ~ 4 kev peak gaγγ & gaee < 1.1x10-1 Nuclear de- excitagon: : gan & gaee due to the temperature of the sun low energy excited state is highly populated 57Fe is the best candidate of the source of axions. Non linear energy response causes the shin of the energy of the 14.4 kev signal 12/07/25 Y. in Chicago 21

22 Refurbishment PMT Al- seal Difficult to remove Installa;on of Cu ring around the PMT quartz window Place a Cu- cover between PMTs Remove GORE- TEX Clean up surface è 1/100 reduc;on of BG Al- BG quarts PMT body Dis- assemble of the detector has started in July Aner refurbishment 10 kev 12/07/25 Y. in Chicago 22

23 Time schedule XMASS- I refurbishment XMASS- I Physics run XMASS- 1.5 Design, R&D construcgon Physics run JFY 2012 JFY 2013 JFY 2014 JFY 2015 JFY ton (1 ton fiducial) detector, BG 10-5 /kev/kg/day SensiGvity; s SI < cm 2 (higher mass), <10-42 cm 2 (low mass DM) DM Axions, Solar Axions XENON1t commissioning 12/07/25 Y. in Chicago 23

24 Summary Around 5 kev region, we have more than 2 orders of magnitude larger BG than originally es;mated. They are from PMT Al seal and Cu surface 210Pb. Below 5 kev, there may be a contribu;on from 14C contaminated in GORE- TEX, but not confirmed yet. There may be unknown BGs or something else. For the whole volume analysis, we have obtained similar/be[er sensi;vi;es to/than other current experiments. Low mass dark ma[er search, Annual varia;ons, Axion dark ma[er and Solar axions Thanks to the XMASS large total mass, low threshold, sensi;vity to the electro- magne;c events as well as nuclear recoils Fiducial volume analysis is under evalua;on. Refurbishment to remove those backgrounds will be done in next several months and we will expect one to two orders of magnitude improvements. XMASS 1.5 design work will start soon, hope to start to take data in 2015 (not funded yet). 12/07/25 Y. in Chicago 24