Light Dark Matter and XENON100. For the XENON100 Collaboration Rafael F. Lang Columbia University

Transcription

1 Light Dark Matter and XENON100 For the XENON100 Collaboration Rafael F. Lang Columbia University

2 The XENON Collaboration ~60 scientists from 12 institutions: University of California Los Angeles Rice University Houston Columbia University New York Universidade de Coimbra Subatech Nantes NIKHEF Amsterdam Willhelms Universität Münster Max-Planck-Institut Heidelberg Universität Zürich Laboratori Nazionali del Gran Sasso INFN e Università di Bologna Jiao Tong University Shanghai Rafael F. Lang: Light Dark Matter and XENON100 2

3 Particle Detection Channels WIMP XENON10/100/1t,, ZEPLIN-II/III, LUX, WARP Scintillation ZEPLIN-I, KIMS, DAMA, LIBRA Target Ionization CoGeNT, GENIUS-TF, HDMS XENON100? CRESST-II Phonons CRESST-I, CUORICINO CDMS, EDELWEISS Bubble Nucleation COUPP Rafael F. Lang: Light Dark Matter and XENON100 3

4 Dual-Phase Xenon TPC top PMT array anode + 3D position information S2 hit pattern: drift time: gas xenon liquid xenon e - e - e - cathode - bottom PMT array S1 drift time S2 Rafael F. Lang: Light Dark Matter and XENON100 4

5 Recoil Discrimination > 99% e - / : electron recoil n/wimps: nuclear recoil S1 S2 S1 S2 lots of information for each event Rafael F. Lang: Light Dark Matter and XENON100 5

6 Recoil Discrimination > 99% e - / : electron recoil n/wimps: nuclear recoil 10keV nr WIMP yields ~160 S1 photons, detect ~10 ~70 S2 electrons, generate ~10 4 photons, detect ~1750 S1 S2 Rafael F. Lang: Light Dark Matter and XENON100 6

7 XENON PMT top array 80 PMT bottom array Rafael F. Lang: Light Dark Matter and XENON100 7

8 XENON100 veto PMT bell 98 PMT top array +4500V PTFE TPC, field shaping 160kg liquid xenon 80 PMT bottom array veto PMT V Rafael F. Lang: Light Dark Matter and XENON100 8

9 PMTs & Gain Calibration 1 square metal-channel R Al optimized for 178nm, low T, high p low radioactivity <1mBq in 238 U/ 232 Th per PMT 98 top PMTs, optimized for good r resolution 80 bottom PMTs, optimized for filling factor, QE ~33% 64 in veto looking up, down and inward regular gain monitoring Rafael F. Lang: Light Dark Matter and XENON100 9

10 Design for Electric Field hexagonal electrode meshes cathode at -16kV drift field 0.53kV/cm anode at 4.5kV extraction field 6kV/cm (LXe) 12kV/cm (GXe) 40 doubled field shaping rings Rafael F. Lang: Light Dark Matter and XENON100 10

11 DAQ 242 PMTs 400 s waveform 100MS/s, 14bit flash ADC zero-length-encoding (on-board FPGA) dead-time free during background data taking (1km of cables inside the detector, 3km outside) Rafael F. Lang: Light Dark Matter and XENON100 11

12 Gran Sasso Underground Lab Gran Sasso mountain range cable car to ski resort highway lab hiking path tunnel Assergi Rafael F. Lang: Light Dark Matter and XENON100 12

13 XENON100 Shield 20cm H 2 O, 15cm Pb, 5cm French Pb, 20cm PE, 5cm Cu Rafael F. Lang: Light Dark Matter and XENON100 13

14 Screening & Simulation dedicated HPGe LNGS simulation agrees with data Rafael F. Lang: Light Dark Matter and XENON100 14

15 Spatial Distribution gammas: main contribution from PMTs highly localized neutrons: Rafael F. Lang: Light Dark Matter and XENON100 15

16 Firestone The Other Noble Gas in Xenon 81 Kr: 281keV electron capture, long decay, abundance 81 Kr/Kr ~ irrelevant but 85 Kr beta decays (687keV), natural abundance 85 Kr/Kr ~ use dedicated distillation column to get Kr to ~100ppt level Rafael F. Lang: Light Dark Matter and XENON100 16

17 How to Ensure Kr at That Level? 85 Kr 99.6% Q =687 kev 10.8y 0.4% 85 Rb 514 kev 1.0 s stable use delayed - -coincidence to tag events in situ only 0.4% branching XENON100: tagged 6 events in 60.6 live days S2 Rafael F. Lang: Light Dark Matter and XENON100 17

18 Example with Full 30cm Drift S1: 498pe S2: 41609pe electron lifetime during background data taking 154 s to 192 s drift 174μs Rafael F. Lang: Light Dark Matter and XENON100

19 measured resolution / mm Position Reconstruction test with collimator: resolution < 3mm (~anode mesh pitch) SVM NN 2 40kg fiducial set radius / mm Rafael F. Lang: Light Dark Matter and XENON100 19

20 Position Dependent Corrections S1 light collection S2 electron lifetime S2 x-ydependence Rafael F. Lang: Light Dark Matter and XENON100 20

21 Calibration with 83m Kr 83 Rb Q EC =910 kev 86 d 92% 83m Kr h 83 Kr 147 ns stable decay drift Rafael F. Lang: Light Dark Matter and XENON100 21

22 Position Dependent Corrections 137 Cs taken with low anode Rafael F. Lang: Light Dark Matter and XENON100 22

23 S1 r-z-correction Rafael F. Lang: Light Dark Matter and XENON100 23

24 S2 z-correction (electron lifetime) Rafael F. Lang: Light Dark Matter and XENON100 24

25 S2 x-y-z-correction Rafael F. Lang: Light Dark Matter and XENON100 25

26 events / kg Inelastic Scatters & Fiducialization Electronic recoils during 241 AmBe calibration: full volume 30kg fiducial energy / kevee Rafael F. Lang: Light Dark Matter and XENON100 26

27 Single Electrons typical waveform: Rafael F. Lang: Light Dark Matter and XENON100 27

28 Single Electrons time correlation: typical waveform: time constant Rafael F. Lang: Light Dark Matter and XENON100 28

29 Single Electrons position correlation: typical waveform: time constant Rafael F. Lang: Light Dark Matter and XENON100 29

30 Single Electrons low S2 spectrum: typical waveform: time constant Rafael F. Lang: Light Dark Matter and XENON100 30

31 Nuclear Recoil Equivalent Energy Nuclear Recoil Energy: L y (122keV ee ) = ( )PE S ee = 0.58 S nr = 0.95 astro-ph/ Rafael F. Lang: Light Dark Matter and XENON100 31

32 Nuclear Recoil Equivalent Energy Nuclear Recoil Energy: L y (122keV ee ) = ( )PE S ee = 0.58 S nr = 0.95 best fit systematic uncertainty Manzur et al Aprile et al Chepel et al Aprile et al Akimov et al Bernabei et al Arneodo et al best fit Rafael F. Lang: Light Dark Matter and XENON100 32

33 XENON100 Data Taking formally a non-blind analysis since data was open, in reality analysis developed on calibration data only Rafael F. Lang: Light Dark Matter and XENON100 33

34 Quality Cuts from Calibration reject PMT single PE: require one two-fold coincident S1 pulse in the waveform reject double scatters: require one S2>300PE and no signal in veto during 20ns around the S1 pulse reject electronic artifacts: no obvious noise reject events not from fiducial volume: S2 width consistent with drift time Rafael F. Lang: Light Dark Matter and XENON100 34

35 Nuclear Recoil Band Neutrons from 241 AmBe energy range kev r (4-20 PE, S1 coincidence with >90% efficiency above 4PE) and below nuclear recoil median Rafael F. Lang: Light Dark Matter and XENON100 35

36 Electron Recoil Band Compton scatters from 60 Co 50% nuclear recoil acceptance gives >99% discrimination at low energies Rafael F. Lang: Light Dark Matter and XENON100 36

37 Cut Acceptance consider every event cut by only one cut as valid event expect improvements of cuts in the future Rafael F. Lang: Light Dark Matter and XENON100 37

38 Discrimination days, 40kg fiducial, 30%-40% efficiency no events close to or below the nuclear recoil median even below 4PE Rafael F. Lang: Light Dark Matter and XENON100 38

39 Discrimination days, 40kg fiducial: (no events even at 84% acceptance) Rafael F. Lang: Light Dark Matter and XENON100 39

40 Fiducialization days, 40kg fiducial, 30%-40% efficiency no nuclear recoils anywhere near the fiducial volume Rafael F. Lang: Light Dark Matter and XENON100 40

41 Resulting Limit characteristic velocity 220km/s, Earth velocity 232km/s, escape velocity 544km/s, local density 0.3GeV/cm 2, Helm Formfactor, Poisson dominated energy resolution Rafael F. Lang: Light Dark Matter and XENON100 41

42 Resulting Limit excludes CoGeNT and DAMA favored regions at 90% c.l. robust: fiducial volume, discrimination, cut acceptance, energy threshold all very conservative! on the arxiv tomorrow Rafael F. Lang: Light Dark Matter and XENON100 42

43 Rafael F. Lang: Light Dark Matter and XENON100 43