Direct Detection in the next five years: Experimental challenges and Phonon Mediated Detectors

Transcription

1 Direct Detection in the next five years: Experimental challenges and Phonon Mediated Detectors Complementarity between Dark Matter Searches & Collider Experiments Miniworkshop before SUSY06 at Irvine - June 10, 2006 CDMS-II Co-Spokesperson & SuperCDMS Spokesperson Summary of current status of Direct Detection CDMS-II, EDELWEISS, ZEPLIN-I, CRESST, WArP DAMA, LIBRA(?), NAIAD Short term perspectives (< 5 years) SuperCDMS, EDELWEISS-II, CRESST-II ZEPLIN-II/III, XENON, WArP, ArDM, CLEAN PICASSO, SIMPLE, COUPP, SIGN, Xe gas Long term perspectives (> 5 years) Page 1

2 NRC EPP2010 Report on US HEP Program Action Item 1: US participation in LHC Action Item 2: US R&D for ILC Action Item 3: US bid to host ILC Action Item 4: US particle astrophysics ($$x2-3) Direct detection of dark matter Precision measurements of CMB Measure properties of dark energy Action Item 5: US neutrino physics The direct detection of dark matter in terrestrial laboratories, which then could be combined with measurements of candidate dark matter particles produced in accelerators. Action Item 6: Limited participation in large scale high precision experiments Page 2

3 The Signal and Backgrounds Signal (WIMPs) Background (gammas) Nucleus Recoils E r Electron Recoils E r v/c E r 10 s KeV phonons v/c 0.3 ionization Neutrons also interact with nuclei, but mean free path a few cms Surface electrons from beta decay can mimic nuclear recoils χ 0 γ Page 3

4 Cross-section [cm 2 ] (normalised to nucleon) LCC1 Excluded by Accelerators Does the LHC supplant Direct Detection? Excluded by Direct Detection DAMA LHC only WIMP Mass [GeV] CDMS II 2005 EDELWEISS ZEPLIN I ILC only CDMS II 2007 SuperCDMS 25kg CDMS is cross section-limited TeV WIMPs detectable, direct connection to cosmology Page 4 Accelerators are mass-limited spectral info, but often can t see LSP or deduce its relic density

5 Direct Detection and Colliders E.A. Baltz, M. Battaglia, M.E. Peskin, and T. Wizansky, hep-ph/ (120 pages) no direct detection information including SuperCDMS 25 kg experiment Page 5

6 Supersymmetry at Tevatron vs CDMS M. Carena, D. Hooper, P. Skands, hep-ph/ Tevatron 2005 CDMS current results rule out most Tevatron parameter space CDMS 2007 reach can rule out Tevatron reach or find SUSY CDMS 2005 channel would be obtained as long as the Higgsino fraction of the lightest neutralino is greater than about 0.5% and m A is heavier than about 140 GeV (as inferred from Fig. 1 and Eq. 4). On the other hand, evidence for the production of heavy neutral Higgs bosons at the Tevatron, without the observation of 2007 neutralino dark matter at CDMS by 2007, could give very valuable information about the MSSM particle spectrum. In particular, it would suggest that µ is large, e.g. greater than about 800 GeV (see Fig. 2). CDMS 3Tevatron 2007 CAVEATS Complemenatrity FIG. 2: The regionsdddm in the M& 2 -µ LHC/ILC plane in which the possibility of Page discovering heavy, neutral MSSM Higgs boson at the Tevatron (4 fb 1 per experiment) through p p A/H X τ + τ X is excluded due to current CDMS limits (light shaded/green) and the projected 2007 CDMS limits (black). The (blue) shaded region along the bottom of the figure and extending upward for small µ is excluded by LEP The conclusions presented in this letter are subject to a number of assumptions. Most obviously, if the dominant component of our universe s dark matter is not made up of neutralinos, then the constraints 6 Blas Cabrera placed by - Stanford CDMS do not University affect collider searches for supersymmetry. The results from CDMS involve substantial astrophysical uncertainties. Primary among these is the local dark matter density, which we have taken to be 0.3 GeV/cm 3, as im-

7 Present sensitivity 1 kg experiments ZBG σ nw ~ cm 2 Current Status 2T CDMS-II, EDELWEISS, CRESST, ZEPLIN-I XMASS, WArP 2.3 l Page 7

8 CDMS-II SI Results & other experiments DAMA WIMP-nucleon cross-section [cm 2 ] DAMA 99% c.l. CDMS (Soudan) WARP (42 kev) CRESST EDELWEISS WIMP mass [GeV] For further details see PRL 96, (2006) New result from WArP 2.3 liter prototype Page 8

9 Spin Dependent WIMP limits Spin-sensitivity from 73 Ge (J=9/2, 7.7%) and 29 Si (J=1/2, 4.7%) n scattering p scattering CRESST I CDMS Si CDMS II Si DAMA/NaI PICASSO CRESST I CDMS II Ge PICASSO CDMS II Si ZEPLIN I CDMS II Ge DAMA/NaI NAIAD Majorana ν Super-K Majorana ν For further details see PRD D73, (2006) Page 9

10 Reach of Underground Laboratories Reduce n from μ 2000 mwe 1,000 kg-d cm mwe 10,000 kg-d cm mwe 100,000 kg-d cm 2 Log 10 (Muon Flux) (m -2 s -1 ) Depth (meters water equivalent) Page 10

11 ST1&2 Soudan -> SNOLab like Tower 1 SUF -> Soudan Tower 1 (4 Ge & 2 Si) at SUF then at Soudan 19 neutron events at SUF 0 events at Soudan Page 11

12 Run 118 (1T) & Run 119 (2T) in Soudan Page 12

13 CDMS Active Background Rejection Detectors with excellent event-by-event background rejection Measured background rejection: % for EM backgrounds using charge/heat 99.4% for β s using pulse risetime as well Much better than expected in CDMS II proposal! Tower of 6 ZIPs Tower 1 4 Ge neutrons betas gammas gammas 2 Si betas Tower 2 2 Ge 4 Si neutrons Page 13

14 Number of Alpha Events (>P <Q) Measurement of Beta backgrounds From coincident events between detectors we identify gaps Z1-2, Z2-3, Z3-4, Z4-5, and Z5-6. Correlation of alpha decays (5.3 MeV 210 Po) with beta decays (46 kev sum both sides from 210 Pb). So 210 Pb on surfaces of detectors ~50% of our singles beta background. Small contributions from ϒs & radioisotopes, e.g. 14 C, 40 K Page Tower 1 Tower 2 1 evt <=> 0.5x10-3 / cm 2 -d Number of Beta Events (46 kev We have reduced Rn exposure for detectors in Towers 3-5 and expect >x2 reduction. We will soon measure alphas & betas.

15 Identification of alphas and betas Page 15

16 1.5 WIMP search data (5 Ge ZIPs ~53 kg-d) Prior to phonon pulse shape timing cuts 10.4 kev Gallium line 1.5 After timing cuts, which reject most electron recoils Z2/Z3/Z5/Z9/Z11 Ionization Yield Z2/Z3/Z5/Z9/Z Recoil Energy (kev) CDMS has demonstrated < 4 evt / kg of Ge / yr Ionization Yield candidate (barely) 1 near-miss Recoil Energy (kev) Background ESTIMATE: 0.37 ± 0.20 (sys.) ± 0.15 (stat.) electron recoils, 0.05 recoils from neutrons expected Page 16

17 Improvements in Surface Event Rejection Significant improvements in our analysis of phonon timing information Surface event rejection improved by x3; kept pace with exposure increase! Cuts are set from calibration data (blind analysis) We still have more discrimination power available as needed Can continue to keep backgrounds < 1 event as more data accumulates This is the real strength of CDMS detectors! Surface Events Optimize background rejection versus nuclear recoil efficiency Neutron Efficiency Neutrons Chi-square (background pulse shape) - Chi-squared (neutron pulse shape) Page 17

18 Strategy for Search Protocols Maximum exposure - Cross-section for direct detection now below cm 2 which corresponds to one event per 30 kg-d with 100% efficiency and 10 kevr threshold. Zero background best for discovery. Insitu calibrations - demonstrating insitu positions and stability of electron recoils versus nuclear recoil events and blinding. Blind analysis - Hide the WIMP search region during the determination of analysis strategy including cuts and software thresholds. Full detector modeling for MCs. Bar is set high as it should be! Page 18

19 Comparisons for SI Sensitivity comparison for all target materials have chosen typical thresholds for a cross section of 1e-8 pb how many kg-d per count on average dr/dq [cts/kev!kg!d] 3 2 1! "n = 1e!44 cm 2 ; m " = 60 GeV 4 x 10!4 Na/Ne(7 kev) 2824 kg!d/ct Si(10 kev) 2031 kg!d/ct Ar(20 kev) 1284 kg!d/ct Ge(10 kev) 313 kg!d/ct I/Xe(16 kev) 309 kg!d/ct W(16 kev) 385 kg!d/ct Recoil Energy [kev] Page 19

20 Technology Complementarity NaI - annual modulation with no discrimination (<6 pe/kev) DAMA signal is suspect because near threshold (systematics) LIBRA kg new installation (still no discrimination) Cryogenic technologies - lowest intrinsic threshold (10 6 phon/kev) (Super)CDMS Ge & Si ionization + phonon + timing (now best) EDELWEISS Ge thermal + ionization (no timing) CRESST CaWO 3 thermal + scintillation (no light for W) Liquid/gas Xe Ar Ne - intrinsically high threshold (~1 pe/kev) ZEPLIN I & XMASS scintillation (uncalibrated result) XENON scintillation + ionization (need demo of threshold & stability) WArP very impressive first result, ArDM, CLEAN Superheated liquids - no energy resolution (counting) PICASSO, SIMPLE, COUPP CF 3 Br & CF 3 I (need demo of stability) TPC DRIFT - good for directionality (near term not enough mass) Page 20

21 Discrimination strategies Most particle physics experience in MeV range Direct detection requires kev scale Poor statistics from scintillation CRESST Scintillation ~ 1 kev/γ Phonons 10 mev/ph ZEPLIN XENON WArP, ArDM CLEAN CDMS EDELWEISS Ionization ~ 10 ev/e Page 21

22 Threshold comparison and importance Best resolution from sub-k experiments allows better discovery potential In the end, the tails of the background distributions determine the sensitivity Best CDMS Ge ZIP gammas XENON Prototype 99% discrimination to below ~10 kev overlap starts at ~50 kev counting statistics for more detail see n-recoils edu/hep/dm06/ talks/shutt.pdf S2 Threshold Page 22

23 EDELWEISS 1 event / 7 kg-d 1.5 EDELWEISS Experiment Phonon runs - Physics EDELWEISS-I GSA1+GSA3+GGA3 (22.7 kg.d) Ionization/Recoil Ratio 1 0.5! bands "=90% "=99.9% Recoil Energy (kev) nuclear recoil bands "=90% Edelweiss-II 320 g Ge Page 23

24 CRESST No light from W CRESST Experiment Page 24

25 Next two years 10 kg experiments ZBG σ nw ~ cm 2 5T CDMS-II, EDELWEISS, CRESST, ZEPLIN-II, XENON-10, WArP-140, ArDM Page 25

26 About to Operate Five Towers in Soudan Tower 1: 4 Ge & 2 Si Tower 2: 2 Ge & 4 Si Tower 3: 4 Ge & 2 Si Tower 4: 4 Ge & 2 Si Tower 5: 5 Ge & 1 Si Page 26

27 Current Status in Soudan Mine Completed run demonstrating successful operation of cryocooler with vibration isolation. Vacuum system better than ever and dilution refrigerator reached base temperature < 20 mk. But detectors remained at mk (spec < 50 mk). We have identified the likely cause to be increased heat through graphite thermal isolators, together with decreased conductance of oxide on Cu connections to DR. Thermal model consistent with all observations, and we have confirmed with tests at UCB and Case facilities - standard cryogenic engineering. We now have low-risk plan for completing CDMS-II science goals by end of calendar Page 27

28 In five years 100 kg experiments ZBG σ nw ~ 10 Current Status -45 cm 2 SuperCDMS 25, EDELWEISS-II, CRESST-II, WArP 140, XENON 100,... Page 28

29 SuperCDMS is approved to be sited at SNOLab SuperCDMS at SNOLab We have received strong interest from Canadian collaborators - Queens... New lab space (under construction - ready in 2007) Sudbury, Ont. CA Sudbury Neutron Obs. Page 29

30 Exploring cryocooler system with little or no cryogen servicing Cryogen-free! dilution fridge Schematic of new SNObox 20.00" OVC-Pb-! poly lid! o" as unit 24.00" Electronics box Pulse tube! cryocooler Lid! splits 40.00" 76.00" " OVC IVC Outer polyethylene 36.00" 72.00" " Page 30

31 SuperCDMS 25 kg detectors Mass from 0.25 kg to 0.64 kg Improve by x100 x2.5 V/S, x2 lower betas x5 improved analysis x2 H passivate, x2 risetime Page 31

32 DM Direct Search Advances (2006) 58,000 kg-d ~1 event kg -1 day -1 LAr ~1 event 100 kg -1 yr -1 CRESST 04 CRESST II 230 kg-d WArP 90 kg-d 70 kg-d Need zero bkgd experiments to make progress. SuperCDMS 25 kg WArP 140 SuperCDMS 150 kg / EUREKA Plot updated from that in DM Review Article: Gaitskell, Ann. Rev. Nucl. and Part. Sci. 54 (2004) Page 32 SuperCDMS 25 kg

33 Conclusions Best sensitivity now cm 2 (10-7 pb) sensitivity for spin independent (1 kg detector mass scale); now CDMS-II 2T, soon EDELWEISS, CRESST, ZEPLIN II, WArP 2.3 l, XENON 10. By end of 2007 existing experiments will reach cm 2 (10-8 pb)(10 kg detector mass scale); CDMS-II 5T, EDELWEISS II, CRESST II, ZEPLIN II/III, WArP 140, XENON 10 Within five years next generation to reach cm 2 (10-9 pb) (100 kg detector mass scale); SuperCDMS 25 kg, EDELWEISS II, CRESST II, ZEPLIN IV, XENON 100, WArP, ArDM, CLEAN SuperCDMS 25 EXPERIMENT READY TO START NOW MULTIPLE TECHNOLOGIES ARE NECESSARY WE NEED TO CONVINCE DM SAG & P5 DURING 2006 Page 33