Toward a next-generation dark matter search with the PICO-40L bubble chamber. Scott Fallows TAUP2017 Laurentian University 24 July 2017

Transcription

1 Toward a next-generation dark matter search with the PICO-40L bubble chamber Scott Fallows TAUP2017 Laurentian University 24 July 2017

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3 Other PICO talks at TAUP First demonstration of a scintillating xenon bubble chamber for dark matter and CEνNS detection (J. Zhang) Mon 1:15pm Threshold verification in the PICO-60 detector and study of the growth and motion of nucleation bubbles (P. Mitra) Mon 2:45pm PICO Results and Outlook *plenary (C. Krauss) Tue 9:50am Calibrating Inner-Shell Electron Recoils in a Xenon Time Projection Chamber (D. Baxter) Tue 1:15pm PICO-500: Simulations for a 500L Bubble Chamber for Dark Matter Search (E. Vázquez Jáuregui) Tue 4:30pm 3

4 PICO posters at TAUP Nuclear recoil calibration for PICO bubble chambers (M. Jin) PICO-60: World s largest bubble chamber for dark matter detection (U. Chowdhury) The PICO-40L detector design (B. Loer) 4

5 Overview Bubble chambers for dark matter direct detection and the PICO programme PICO-40L: Right side up (RSU) detector design: hardware improvements and background reduction Commissioning and operations timeline Projected physics reach Proposed tonne-scale chamber: PICO-500 5

6 Bubble chamber principle Lower pressure in target liquid until it is in metastable superheated state Energy deposition nucleates small bubble that grows to visible size Cameras watch for visible bubble and issue the primary trigger compressed expanded superheated 6 (plots by Eric Dahl)

7 Gamma rejection Choose thermodynamic parameters for sensitivity to nuclear recoils, but not electron recoils 7

8 Gamma rejection Probability of Nucleation C 3 F 8 Gamma Rejection by Chamber CF3 I PICO-60 PICO-0.1 U Chicago COUPP-1L Queen's COUPP-4 PICO-2L PICO-60 We can set the threshold Aim for this level for 1-year exposure on de/dx (E T /r c ) Threshold (kev) Various PICO Detectors (Dan Baxter, Conference on Science at SURF, May 14, 2017) 8

9 Neutron WIMP search Counts Acoustic discrimination (Aubin et al., New J. Phys.10:103017, 2008) Alphas deposit their energy over tens of μm Neutron WIMP search log(ap) NN score Nuclear recoils deposit energy over tens of nm Counts Acoustic discrimination against alphas discovered 0.5 by PICASSO NN score AP distributions for AmBe and FIG. 2. Top: Cf neutron calibration data (black) and WIMP search data (red) at In PICO, alphas are several times louder than recoils 3.3 kev threshold. Bottom: AP and NN score for the same 0-1 0region 1for nuclear dataset. The acceptance recoil candidates, For a WIMP-search run, the acoustic signals are log(ap)data unmasking using defined before WIMP search acoustic neutron calibration data, are displayed with dashed lines and blinded in order to set an unbiased cut on this 252 FIG. 2. Top: events AP distributions for AmBe and CfAlphas neureveal no candidate in the WIMP search data. acoustic parameter ( AP ) tron 222 calibration data (black) and WIMP search data (red) at from the3.3 Rn threshold. decay chain can be by their time sigkev Bottom: APidentified and NN alphas score for the same neutrons nature and populate the two region peaksfor in nuclear the WIMP search data dataset. The acceptance recoil candidates, Observable bubble ~mm 214 before energy WIMP search acoustic unmasking using at high defined AP. Higher alphas from datapo are producing neutron calibration ~40 μm larger acoustic signals. data, are displayed with dashed lines and ~50 nm Daughter heavy nucleus (~100 kev) reveal no candidate events in the WIMP search data. Alphas from the 222 Rn decay chain can be identified by their time signature and populate the two peaks in the WIMP search data at high AP. Higher energy alphas from 214 Po are producing (0.96 larger±acoustic signals.± 0.34) single(multiple)-bubble to be events. PICO-60 was exposed to a 1 mci 133 Ba source Helium nucleus Multiple radiating bubbles both before and after the WIMP search data, which, (~5 MeV) to be 0.25 ± a0.09 (0.96 [21] ± 0.34) single(multiple)-bubble compared against Geant4 Monte Carlo simulation, F s w ( a t T h p m s ( p

10 Backgrounds checklist Gammas/betas: de/dx threshold in superheated detectors affords intrinsic rejection ~10-11 for typical PICO energy thresholds Alpha decays: large acoustic signals allow discrimination at >99.4% (stats. limited) Neutrons: reject multiple scatters visually, veto detector-adjacent cosmogenics, minimize other sources (extensive material screening, shielding) 10

11 The PICO programme PICO was formed from merger of PICASSO and COUPP collaborations Small surface test chambers at UdeM, Queen s, Northwestern, Drexel, NEIU PICO-2L C3F8 ( ) C. Amole et al., Phys. Rev. Lett. 114, (2015) C. Amole et al., Phys. Rev. D 93, (2016) PICO-2L C3F8 PICO-60 CF3I (2013) C. Amole et al., Phys. Rev. D 93, (2016) PICO-60 C3F8 ( ) C. Amole et al., Phys. Rev. Lett. 118, (2017) PICO-40L ( ) PICO-500 (future) PICO 11 COUPP-60 PICO-60 CF3I, C3F8

12 First PICO-60 physics run 1 See plenary talk Tuesday 9:50am (C. Krauss) for details 30 live-day run at 3.3 kev threshold, published in PRL*: a background-free 1167 kg-day WIMP-search exposure Factor of 17 improvement in upper limit on spin-dependent WIMP-proton cross-section Additional blinded exposure acquired, expected to be background limited NN score Counts SD WIMP-proton cross section [cm 2 ] Counts NN score Neutron WIMP search Neutron WIMP search log(ap) FIG. 2. Top: AP distributions for AmBe and 252 Cf neutron calibration data (black) and WIMP search data (red) at kev threshold. Bottom: AP and NN score for the same dataset The acceptance region for nuclear recoil candidates, defined before -1 WIMP0 search1acoustic 2 data unmasking 3 4 using neutron calibration data, are displayed log(ap) with dashed lines and reveal FIG no candidate events in the WIMP search data. Alphas from the Top: Rn decay AP distributions chain can be for identified AmBeby and their 252 Cf time neutron calibration and populate data the (black) two peaks and WIMP in thesearch WIMPdata search (red) data at3.3 high kevap. threshold. Higher energy Bottom: signature 17x alphas AP and fromnn 214 score Po are for producing the same dataset The acceptance region forsuperk larger acoustic signals. nuclear recoil candidates, defined before WIMP search acoustic data unmasking using neutron calibration data, are displayed with dashed lines and PICO-60 C 3 F reveal no candidate events 8 in the WIMP search data. Alphas tofrom 10 be -41 the ± Rn0.09 decay (0.96 chain± can 0.34) be identified single(multiple)-bubble by their time signature and populate 10 1 the two peaks in 10 the 2 WIMP search 10 data events. 3 at high PICO-60 AP. Higher was energy exposed alphas to from a mci WIMP mass [GeV/c 2 Po are 133 Ba producing source both larger before acoustic and signals. after the WIMP search ] data, which, 12compared *C. Amole against et aal., Geant4 Phys. Rev. [21] Lett. Monte 118, Carlo simulation, (2017) PICO-2L C3F8 PICASSO PICO-60 CF3I IceCube

13 PICO-40L Goals Science: acquire one-year background-free exposure Order of magnitude improvement on PICO-60 limits Engineering: demonstrate background reduction and technology improvements for PICO-500 Focus on (neutron) background reduction Confirm RSU design used in prototype chambers 13

14 PICO-60 PICO-40L Pressure vessel Cameras Heating element Thermal insulation C 3 F 8 /freon (target) Hydraulic fluid (mineral oil) Thermal gradient (no water buffer) Bellows 14

15 PICO-40L detector design To be deployed 2 km underground at SNOLAB ( ladder labs area) Target: ~40L C 3 F 8, (proj. >90% fiducial) Synthetic fused silica inner vessel and piston (no more water piston ) Larger stainless steel pressure vessel, 20t water tank, muon veto all minimize neutron backgrounds Normal (-25C) Superheated (15C) 15

16 PICO-40L detector design Inversion eliminates potential sources of background: water droplets surface tension effects particulates would now fall out of active region into cold annulus No buffer: allows wider choice of target fluid, wider range of operating temperatures; directly enables full target recirculation and purification Normal (-25C) Superheated (15C) 16

17 Many upgraded systems Optics/DAQ: much better Basler cameras using new Sony IMX174 CMOS sensor running on newer USB3 Vision interface for more programming flexibility better lenses (higher resolution, reduced barrel distortion, etc.) better stereoscopic viewing angles and camera mounts better retroreflector and improved LED lighting rings Basler CMOS camera with new IMX714 sensor Hydraulic system control: brought into alignment with new designs used on several test chambers; will enable continuous active recirculation/filtration Piezo acoustic sensors: better physical coupling, and improved longevity in different hydraulic fluid (mineral oil rather than propylene glycol) 17

18 PICO-40L timeline Pressure vessel arrived to SNOLAB surface 18 May 2017 Clean surface commissioning ongoing presently Full detector assembly to be shipped underground to SNOLAB Dec 2017 First data January 2018 End of physics data in

19 PICO-500 Proposed tonne-scale detector See talk Tuesday 4:30pm (E. Vázquez Jáuregui) for details Could begin surface commissioning as soon as late 2018 (cf. PICO-40L) Goal is to begin data-taking in PICO-500

20 PICO Designed to have an additional order of magnitude sensitivity beyond PICO-40L Could run C 3 F 8 and/or several other targets (i.e. CF 3 I or hydrocarbons: C 2 H 2 F 4, etc.) to probe higher/lower mass or reduce a WIMP signal in a predictable way SD WIMP-proton cross section [cm 2 ] LUX PICO-2L PICO-60 CF3I PICO-60 C3F8 PICO-40 (proj) IceCube C3F8 neutrino bkgd WIMP mass [GeV/c 2 ] 20

21 PICO Designed to have an additional order of magnitude sensitivity beyond PICO-40L Could run C 3 F 8 and/or several other targets (i.e. CF 3 I or hydrocarbons: C 2 H 2 F 4, etc.) to probe higher/lower mass or reduce a WIMP signal in a predictable way SD WIMP-proton cross section [cm 2 ] LUX PICO-2L PICO-60 CF3I PICO-60 C3F8 PICO-40 (proj) IceCube PICO-500 (proj) C3F8 neutrino bkgd WIMP mass [GeV/c 2 ] 21

22 Summary and outlook PICO-40L commissioning now, data early 2018 Demonstrate background reduction advances enabling tonne-scale bubble chamber PICO-500 One year background-free running to produce order of magnitude improvement on PICO-60 result PICO-500 could begin data taking as early as 2019 Sensitivity to additional order of magnitude beyond PICO-40L, covering significant new well motivated parameter space Could check itself/signals from other detectors with a target change 22

23 Extra slides

24 PICO-500 Designed to have an additional order of magnitude sensitivity beyond PICO-40L Could run C 3 F 8 and/or several other targets (i.e. CF 3 I or hydrocarbons: C 2 H 2 F 4, etc.) to probe higher/lower mass or reduce a WIMP signal in a predictable way SD WIMP-proton/-neutron combined plot 24

25 PICO-500 projection assumptions 250L fiducial 6 live-months at 3.2 kev (expect 6 solar neutrinos/yr), and 12 live-months at 10 kev (0.15 solar neutrinos/yr) Neutron backgrounds: alpha-n: 0.1 singles/yr muon-induced rock: 0.65 singles/yr in a large enough tank muon-induced on detector material assumed veto-able 25