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XENON – Results and Prospects Marc Schumann Physik Institut, Universität Zürich

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XENON – Results and Prospects Marc Schumann Physik Institut, Universität Zürich XENON – Results and Prospects Marc Schumann Physik Institut, Universität Zürich TPC 2010, Paris, December 15 t h , 2010 www.physik.uzh.ch/groups/groupbaudis/xenon/ Dark Matter: (indirect) Evidence NASA/WMAP Dark Matter: (indirect) Evidence NASA/WMAP WIMP Direct Detection: Elastic Scattering of WIMP WIMPs off target nuclei v ~ 230 km/s ER ~ O(10 keV) nuclear recoil Direct WIMP Detection COUPP Tracking: PICASSO Drift, DM-TPC Phonons CDMS CRESST EDELWEISS ROSEBUD Charge Light GERDA XENON DEAP/CLEAN MAJORANA LUX, ZEPLIN DAMA, KIMS CoGeNT WARP, ArDM XMASS Darkside, MAX DARWIN Marc Schumann (U Zürich) – XENON 4 Direct WIMP Detection COUPP Tracking: PICASSO Drift, DM-TPC Phonons CDMS CRESST EDELWEISS TPCsROSEBUD Charge Light GERDA XENON DEAP/CLEAN MAJORANA LUX, ZEPLIN DAMA, KIMS CoGeNT WARP, ArDM XMASS Darkside, MAX DARWIN Marc Schumann (U Zürich) – XENON 5 Direct WIMP Search WIMP Elastic Scattering of WIMPs off target nuclei WIMP v ~ 230 km/s nuclear recoil ER ~ O(10 keV) Recoil Energy: N number of target nuclei Event Rate: ρχ/mχ local WIMP density <σ> velocity-averaged scatt. X-section need information on halo and interaction to get rate Marc Schumann (U Zürich) – XENON 6 WIMP Interactions Detector Requirements Result: Tiny Rates χ - quark (SI, scalar) χ - quark (SD, axial) R < 0.01 evt/kg/day E < 100 keV r Jungmann et al. '96 Phys.Rep. What do we look for? ● nuclear recoils, single scatters ● recoil spectrum falls with E ● dependence on A, spin? ● annual flux modulation? ● other possibilities? iDM, ...? 1 event/kg/yr How to build a WIMP detector? 68% ● large total mass, high A 1 event/ton/yr ● low energy threshold ● ultra low background ● good background discrimination Marc Schumann (U Zürich) – XENON 7 Outline Motivation: Dark Matter ✓ Direct Dark Matter Detection ✓ Some Recent Results XENON100 The Future Marc Schumann (U Zürich) – XENON 8 CDMS: Cryogenic Detectors Located underground in Soudan Lab, Minnesota (USA) Principle: measure charge and heat (phonons) a deposited energy E produces temperature rise ΔT backgrounds n s il o o i c t e R a n z o i tr c n le o E I ils eco ar R ucle N signal Crystals: Ge, Si cooled to few mK Heat low heat capacity good discrimination measurable μK temperature! → „backgound-free experiment“ similar: CRESST, EDELWEISS, Rosebud → BUT: reject surface events via PSA Marc Schumann (U Zürich) – XENON 9 The latest CDMS Result Science 327, 1619 (2010) ● 2 events remain after all cuts after un-blinding ● Background expection: 0.9 0.2 events ● probability for 2 or more events: 23% Marc Schumann (U Zürich) – XENON 10 EDELWEISS-II 400 g Cryogenic Germanium experiment located at LSM InterDigit Electrodes allow fiducialization and surface rejection New preliminary Result: ● 322 kg days ● --4 4 2 5 10 @ 80 GeV/c ● Background starts to show up: 4 events in NR band, 1.9 expected @ 90%CL ● arxiv:1011.2319 Marc Schumann (U Zürich) – XENON 11 The DAMA Observation ● DAMA: PMTs coupled to NaI Scintillators extremely clean background necessary ● looks for annual modulation @ LNGS ● large mass and exposure: 0.82 ton years DAMA interpreted by ● DAMA finds annual modulation @ 8.9 C.L. Savage et al., ● BUT: result cannot be explained with arXiv:0808.3607 standard neutralinos or KK Dark Matter, result in conflict with other experiments DAMA CDMS arXiv: 0804:2741 → arXiv:1002.1028 ZEPLIN III CDMS II XENON10 Marc Schumann (U Zürich) – XENON 12 CoGeNT arXiv:1002.4703 ● CoGeNT: p-type point contact Ge-detector, ultra low noise ● prototype for MAJORANA, operated underground at Soudan ● very low threshold: 0.4 keVee (electronic noise) ● only one observable (charge), some pulse shape discrimination ● Excess at lowest energies → light mass WIMP claim =10- 4 0 cm² (BUT: null hypothesis has similar ²) DAMA 5, 3, 90% CL CoGeNT 90% CL CDMS 90% CL Marc Schumann (U Zürich) – XENON 13 Outline Motivation: Dark Matter ✓ Direct Dark Matter Detection ✓ Some Recent Results ✓ XENON100 The Future Marc Schumann (U Zürich) – XENON 14 Why WIMP search with Xenon? ● efficient, fast scintillator (178nm) ● high mass number A~131: SI: high WIMP rate @ low theshold ● high atomic number Z=54, high density (~3kg/l): self shielding, compact detector ● 50% odd isotopes sensitive to spin-dependent couplings ● no long lived Xe isotopes, Kr-85 can be removed to ppt ● ­ "easy" cryogenics @ 100°C ● scalability to larger detectors ● in 2-phase TPC: good background discrimination Marc Schumann (U Zürich) – XENON 15 Dual Phase TPC Anode Cathode ● ionization/scintillation ratio (S2/S1) allows electron recoil rejection to >99.5% ● 3D position reconstruction in TPC ● Multiscatter Rejection (= discrimination) Marc Schumann (U Zürich) – XENON 16 Localization / Discrimination Discrimination: Co60 AmBe 3D evt localization fiducial cuts multi scatter id. ~99.5% bg rejection @ 50% acceptance (Xe10 performance) definition of WIMP search region Marc Schumann (U Zürich) – XENON 17 The XENON program XENON: A phased WIMP search program 2010-2015: XENON1T 2008-2011: XENON100 2005-2007: XENON10 XENON R&D Columbia Rice UCLA U Zürich Coimbra LNGS SJTU Marc Bologna Schumann (U Zürich)MPIK – XENON NIKHEF Mainz Subatech Münster WIS18 XENON100 Goal (compared to XENON10): ● increase target ×10 ● reduce gamma background ×100 material selection & screening detector design Quick Facts: ● 161 kg LXe TPC (mass: 10 × Xe10 ) ● 62 kg in target volume ● active LXe veto (≥4 cm) ● 242 PMTs ● improved Xe10 shield (Pb, Poly, Cu, H2O, N2 purge) Marc Schumann (U Zürich) – XENON 19 XENON100 Goal (compared to XENON10): ● increase target ×10 ● reduce gamma background ×100 material selection & screening detector design Quick Facts: ● 161 kg LXe TPC (mass: 10 × Xe10 ) ● 62 kg in target volume ● active LXe veto (≥4 cm) ● 242 PMTs (Hamamatsu R8520) ● improved Xe10 shield (Pb, Poly, Cu, H2O, N2 purge) Marc Schumann (U Zürich) – XENON 20 XENON100 Goal (compared to XENON10): ● increase target ×10 ● reduce gamma background ×100 material selection & screening detector design Quick Facts: ● 161 kg LXe TPC (mass: 10 × Xe10 ) ● 62 kg in target volume ● active LXe veto (≥4 cm) ● 242 PMTs XENON10 ● improved Xe10 shield (Pb, Poly, Cu, H2O, N2 purge) Marc Schumann (U Zürich) – XENON 21 XENON100 @ LNGS LNGS: 1.4km rock (3700 mwe) underground since end of February 08 first filled with Xe in mid May 08 extensive calibrations, first science data Marc Schumann (U Zürich) – XENON 22 Selected Calibrations Position dependent Corrections: Cs-137, AmBe inelastic (40 keV), Xe* (164 keV) Kr-83m (planned) Y A R I N Agreement better than 3% I M E L P R Electron Lifetime: Cs-137 (11.2d) (run_08) ~200 µs , up to 400 µs Electron Recoil Band (Background): Co-60, Cs-137, Th-228 Nuclear Recoil Band (Signal): P R E L I M I N A R Y Neutrons: AmBe definition of WIMP search region, discrimination Marc Schumann (U Zürich) – XENON 23 ER / NR Discrimination P R E L I M I N A R Y ● ER/NR discrimination via S2/S1 ratio ● Discrimination efficiency similar to XENON10 (>99%) Marc Schumann (U Zürich) – XENON 24 XENON100 Background run_07 No MC tuning! Using only values from screening. P R E L I M I N A R Y ● 30 kg fiducial mass Measured Background in ● active LXe veto not used for this plot good agreement with ● exploit anti-correlation between light . and charge for better ER-energy scale Monte Carlo prediction Marc Schumann (U Zürich) – XENON 25 Background Comparison Xenon keVee-Scale not precisely known below 9 keVee At low energies this is the lowest Background ever achieved in a Dark Matter Experiment! Marc Schumann (U Zürich) – XENON 26 Nuclear Recoil Scale ● WIMPs interact with Xe nucleus ( and 's produce electron recoils) nuclear recoil (nr) scintillation ● absolute measurement of nr scintillation yield is difficult 5 7 (122keV) measure relative to Co ● relative scintillation efficiency Leff: measurement principle: D e t s h n ie best fit ld lower 90% CL n LXe most recent measurements: New measurement Aprile et al., PRC 79, 045807 (2009) ongoing at Columbia; Manzur et al., PRC 81, 025808 (2010) In preparation in Zürich for discussion of possible systematic errors see Marc Schumann (U Zürich) – XENON A. Manalaysay, arXiv:1007.3746 27 First XENON100 Data ● Background data taken in stable conditions Oct-Nov 2009 ● 11.2 life days ● Data was not blinded ● But: Cuts developed and optimized on calibration data only ● PRL 105, 131302 (2010) ● Energy cut: <30 keVnr arXiv:1005.0380 make use of excellent self- shielding capability of LXe 40 kg fiducial mass Marc Schumann (U Zürich) – XENON 28 A Look at the Bands XENON10 PRL 100, 021303 (2008) XENON100 PRL 105, 131302 (2010) XENON100 updated plot with new Leff values NR acceptance = 50% Background free in 11.2 days cut efficiency ~ 60-85 % after S2/S1 discimination (conservative) Both plots show similar exposure Background expectation ≪1 Marc Schumann (U Zürich) – XENON 29 A first Limit from XENON100 PRL 105, 131302 (2010) arXiv: 1005.0380 This is just a first glimpse! We have much more (blinded) data on tape. WIMP Search Data (run_08, blinded) Published Data Marc Schumann (U Zürich) – XENON 30 New: Alternative Interpretation XENON100 PRL: Best fit limit 90% lower CL Leff limit Alternative Interpretation: Profile Likelihood Method - takes Leff uncertainties into account - uses full log(S2/S1) space - method described in Y arXiv:1007.1727 R A I N M L I E R P Marc Schumann (U Zürich) – XENON 31 WIMP Limits: State of the Art Low WIMP Masses High WIMP Masses T. Schwetz: arXiv:1011.5432 P. Sorensen / XENON10 Talk at IDM2010, to be published CDMS Y R A CDMS II: arXiv:1011.2482
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