Walter C. Pettus on behalf of the DM- Ice collaboration University of Wisconsin Madison. IPA 2015 Madison, WI 4 6 May 2015

Transcription

1 Walter C. Pettus on behalf of the DM- Ice collaboration University of Wisconsin Madison IPA 5 Madison, WI 4 6 May 5

2 Exclusion Limits vs. Low- Mass WIMP Hints Multiple experiments strongly disfavor dark matter interpretation of DAMA Persistent Signal DAMA/LIBRA- phase (.4 ton*yr): Consistent signal modulating with - yr period DAMA/LIBRA CDMSlite SuperCDMS 9.3- σ LUX Agnese et al. Phys Rev Lett (4) Resolution hidden in Astrophysics, Particle Physics, Instrumental Effects, or Background? Bernabei et al. Eur. Phys. J. C 73 (3)

3 Soudan: CDMS CoGeNT Boulby: DRIFT Modane: EDELWEISS Canfranc: ANAIS ArDM Rosebud Homestake: LUX SNOLAB: DEAP/CLEAN PICASSO COUPP DAMIC Gran Sasso: CRESST DAMA/LIBRA DarkSide XENON ANDES: (planned) YangYang: KIMS Jinping: Panda- X CDEX Kamioka: XMASS Stawell: (planned) South Pole: DM- ICE Walter C. Pettus

4 Geographic South Pole Amundsen- Scott South Pole Station Keck Array DM- Ice7 IceCube IceTop BICEP3, SPT 3

5 (x) 8.5- kg NaI(Tl) modules Installed Dec Data run from June Goals: Demonstrate the feasibility of deploying and operating NaI(Tl) detectors in the Antarctic Ice for a dark matter search In situ measurement of the radiopurity of the Antarctic ice / hole ice at 45 m depth Study environmental stability (see Z. Pierpoint, this session) Study the capability of IceCube to veto muons (see A. Hubbard, this session) String #7 String #79 4

6 Commercial flights at ~36,+ ft Sandiviken, SWE Location Relative Neutron Rate (to sea level) Madison, WI.38 South Pole. Commercial Flight 6 Madison, WI, USA Boulby, GBR Polar program flights Storage at 9,3 ft Christchurch, NZL McMurdo Station Low geomagnetic rigidity Walter C. Pettus 5 South Pole Station

7 Full Detector Component History Activation Factor, F tot Cumulative Activation Det Det- Steel Sweden, steel only (historic exposure) Madison, WI (detector construction) Time (days) F tot Relative cosmic ray neutron flux (scaling from sea level) Long periods of low- level exposure during storage and construction Punctuated exposure from flight shipment Cumulative Activation Time- integrated neutron flux scaling Different detector components have different exposure histories Two DM- Ice7 detectors have different deployment times 6

8 Activation Factor, F tot Full Detector Component History Activation Factor, F tot Flight Segments Cumulative Activation Det Det- Steel Time (days) Cumulative Activation 6 SWE - USA Low geomagnetic shielding GBR - USA USA - NZL NZL - McM McM - NPX Lower altitude High geomagnetic shielding Flight Duration (days) 7

9 Calculate sea- level activation: Identify isotopes of interest from activation code (ACTIVIA) Validate cross section against libraries (TENDL, HEAD) Integrate over cosmic ray neutron flux R φ n (E) σ (E) de Cross Section (mb) Production Rate (/kg/day/mev) ACTIVIA TENDL-4 (n) TENDL-4 (p) HEAD-9 Energy (MeV) 3 Scale isotope production by exposure history Allow decay governed by known half- lives Rate (counts / kg / kev / day) All Cosmogenics NaI Crystal 3 Sn m Te 5m Te 7m Te 5 I 8

10 Rate (counts (dru) / kg / kev Rate / day) (dru) DM- Ice7 Det- Data and Residual 3 Data July Sept 5 8 July Residual Sept Residual 6 Triple-Gaussian Fit Sn, m Te X- rays I L- capture 5 I full- energy Confirm identity of cosmogenic peaks: Match simulated spectral features Expect 65.3 kev full- energy and 37.6 kev L- shell capture peaks for 5 I Measuring decay time Expect 59.4 day half- life for 5 I Peak Rate (counts / kg / day) Det- Det- Det- Fit Det- Fit Det- t / = 59. ±.8 days Det- t / = 6.9 ±.6 days Lit. t / = 59.4 ±. days Time (days) 9

11 Examining changing spectrum at high- energy Demonstrates presence of cosmogenic decays 54 Mn (t / = 3 days) and 58 Co (t / = 7 days) Reveals decay of intrinsic contaminants 6 Co (t / = 5.3 yr) in steel pressure vessel Maximally broken 3 Th- chain in steel Rate (dru) Residual Rate (dru) DM- Ice 7 Det- Quarter 4 Quarter Difference Data Cosmogenic Intrinsic Data Diff. Data Simulation 54 Mn 58 Co 6 Co 8 8 Ra - Th - Residual 8 Ac Tl

12 Low- energy spectrum has fewer features, but all cosmogenic: 5 I (t / = 59 days) only low- energy features 3 Sn (t / = 5 days) and m Te (t / = 64 days) Constrained by peaks at 7 kev Provides feedback to energy resolution for simulation Significant overestimate for both 5 I peaks Rate (dru) Residual Rate (dru) Residual Rate (dru) DM- Ice 7 Det- Quarter 4 Quarter Difference Data Data Simulation 3 Sn m Te 5 I Other Decays Residual

13 DM- Ice5N local muon veto! Modular detector supporting deployment in both hemispheres 5 kg NaI(Tl) / module 7- crystal array Sensitivity to test DAMA in 5 kg*yr: ) σ (cm -39 DAMA allowed region (9%C.L., 3σ) Background =.5 Background = Background = Background = 5 Background = DM- Ice5S 5 cm! WIMP mass (GeV) 3

14 DM- Ice5N Few cosmogenic activation concerns - Standard mitigation techniques local muon veto! DM- Ice5S 5 cm! Significant cosmogenic activation concerns - Novel mitigation techniques required 3

15 Event rate one month after deployment Multiple strong cosmogenic calibration lines Significant contributions to 6 kev region of interest Cosmogenic contribution to ROI: 6 I (t / = 3 days) lead contribution at deployment 3 Sn (t / = 5 days) dominates rate over physics run Rate (counts / kg / kev / day) NaI Cosmogenics 3 Sn m Te 5m 7m 5 I 6 I Te Te Rate (counts / kg / kev / day) -6 kev Rate 3 Sn m Te 6 I - - L- shell X- ray or Auger e K- shell X- ray or Auger e - 6 I, 3 Sn, m Te Time (days) 4

16 Exposure budget for 3 Sn in DM- Ice5S: 4% reduction is easy Major contributions remain from NZL- McM flight and South Pole Further reductions: 5% reduction in low- altitude NZL- McM flight (% of total) 9% reduction in South Pole exposure from tunnel storage Reduc&on) EUR),)USA) Stoughton) USA),)NZL) Christchurch) NZL),)McM) McMurdo) McM),)NPX) South)Pole) Walter C. Pettus IPA 5 5

17 Yale University Reina Maruyama, Karsten Heeger, Kyungeun Lim, Estella de Souza University of Wisconsin Madison Francis Halzen, Michael DuVernois, Antonia Hubbard, Albrecht Karle, Matt Kauer, Walter Pettus, Zachary Pierpoint University of Sheffield Neil Spooner, Vitaly Kudryavtsev, Anthony Ezeribe, Frederic Mouton, Matt Robinson, Sam Telfer, Lee Thompson, Dan Walker Boulby Underground Science Facility Sean Paling Fermilab Lauren Hsu University of Alberta Darren Grant Pennsylvania State University Doug Cowen, Ken Clark NIST- Gaithersburg Pieter Mumm University of Stockholm Chad Finley, Per Olof Hulth, Klas Hultqvist, Chistian Walck DigiPen Charles Duba, Eric Mohrmann SNOLAB Bruce Cleveland University of Illinois at Urbana- Champaign Liang Yang 6