DarkSide. Bianca Bottino Università di Genova and INFN Sezione di Genova on behalf of the DarkSide collaboration 1

Transcription

1 DarkSide Bianca Bottino Università di Genova and INFN Sezione di Genova on behalf of the DarkSide collaboration 1

2 DARKSIDE MAIN FEATURES Dark Matter direct detection WIMP induced nuclear recoils Double phase argon Time Projection Chamber (TPC) Ultra low background - Underground laboratory LNGS - Low background materials - Ultra-pure Argon Active neutron tagging to reject neutron induced nuclear recoils and muon veto Powerful background rejection in Argon - Pulse Shape Discrimination (PSD) - Charge/Light ratio (S2/S1) - 3D position reconstruction 2

3 THE LIQUID ARGON CHOICE Pro Contra Relatively dense, cold and easy to purify High ionization and high electron mobility High scintillation yield (40 photons/ kev) Very transparent Exceptional discrimination power, with respect to Xe: Pulse shape discrimination (PSD) Ratio charge/light Intrinsic 39 Ar radioactivity in atmospheric argon (AAr) is the primary background for argon-based detectors Less dense than Xe 3

4 BACKGROUND REJECTION: PULSE SHAPE DISCRIMINATION Two scintillation time constants: - singlet ~7ns -triplet ~1500ns Nuclear and electron recoils have different ratios of singlet and triplet states. Possible discrimination between NR and ER. PSD parameter: f90= light first 90ns total light f f NR ER 4

5 DARKSIDE MULTISTEP PROGRAM DarkSide X DarkSide DarkSide-20k X 5

6 WHY UNDERGROUND ARGON? Problem: 39 Ar cosmogenically activated isotope emits β (τ~269 yr and Q~565 kev): AAr activity ~1 Bq/kg 39 Ar limits the performance of the detector Solution: the 39 Ar contamination in Argon extracted from the Earth s mantle (UAr) is a factor >00 lower than in AAr 6

7 HOW UNDERGROUND ARGON IN DS-50? Extraction of a crude argon gas mixture from CO2 Doe Canyon (Colorado) wells Separation of Ar from He and N2 at Fermilab Shipping to LNGS by sea 7

8 QUALITY OF UNDERGROUND ARGON IN DS-50 s] kg 1 2 AAr Data at 200 V/cm (LSV Anti-coinc.) UAr Data at 200 V/cm (LSV Anti-coinc.) Events / [50 PE < 1/00 39 Ar in UAr < 1 mbq/kg 85 Kr (Global Fit) 39 Ar (Global Fit) S1 [PE] The effective purification factor measured with respect to AAr: (1.4 ± 0.2) 3 8

9 DARKSIDE-50 DETECTOR Three nested detectors: Liquid Argon Time Projection Chamber (TPC): inner detector for WIMP search Liquid Scintillator Veto (LSV): active γ and neutron detector Water Tank (WT): active detector for muons LNGS in Hall C in the Borexino prototype structure 9

10 TPC WT LSV

11 DOUBLE PHASE TPC Double phase argon TPC Two different scintillation signals S1 light produced in liquid argon because of excitation and ionization S2 electroluminescence light produced in gas argon by electrons escaped from recombination 11

12 TYPICAL TPC SIGNALS S2 S1 Position reconstruction Time between S1 and S2 signals gives the vertical position of S1 The distribution of the S2 signal on different PMTs allows x-y reconstruction 12

13 FIRST RESULTS WITH UNDERGROUND ARGON - DS-50 No events in the WIMP search region, with an exposure of 2,616±43 kg d (70.9 live days) f Energy [kev nr ] WIMP search region % 65% 80% 90% 95% 99% S1 [PE]

14 LIMIT EXTRACTED FROM UNDERGROUND ARGON DATA [cm 2 ] σ PandaX-I (2014) PICO (2015) WARP (2007) DarkSide-50 (AAr, 2014) DarkSide-50 (UAr, 2015) DarkSide-50 (combined) XENON0 (2012) 44 CDMS (2015) 45 LUX (2015) PandaX-II (2016) LUX (2016) M χ 2 [GeV/c ] Assuming standard cosmological parameter and considering spinindependent WIMP-nucleon cross section 4 Best limit from an Argon target 14

15 NEXT STEP: DARKSIDE-20K Baseline requirements: Large scale liquid Argon Time Projection Chamber: 20 ton fiducial volume Radiopure construction materials Same veto system design as DarkSide-50 A KEY POINT 15 m 2 radiopure silicon photomultipliers (SiPMs) 15

16 HOW TO GET 30 TONS OF UNDERGROUND ARGON? Urania Expansion of argon extraction plant in Cortez to increase the extraction of UAr Aria Construction of a distillation column in Sardinia to purify UAr 16

17 SIPM Main advantages with respect to PMTs: More compact much lower radioactivity Readout pattern can be chosen at convenience Light yield increase Custom SiPM development for cryogenic temperature by FBK and industrial cooperation for massive production in Abruzzo 17

18 FUTURE EXPECTED SENSITIVITY [cm 2 ] σ CDMS (2015) LUX (2015) WARP (2007) PandaX-I (2014) PICO (2015) DarkSide-50 (2015) XENON0 (2012) PandaX-II (2016) DarkSide-50 (3 yr proj.) LUX (2016) DarkSide-20k (0 t yr proj.) Argo (00 t yr proj.) Coherent neutrino-nucleon scattering floor 2 3 M χ 2 [GeV/c ] 4 18

19 Thanks for your attention! 19