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Search for Dark Ma-er with bubble chambers Orin Harris Northeastern Illinois University APS DPF 2017 1 Bubble chamber: theory In a superheated fluid, bubbles will collapse unless they are large enough (r c ) to overcome surface tension:

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SLIDE 1

Search for Dark Ma-er with bubble chambers

Orin Harris

Northeastern Illinois University

APS DPF 2017

1

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SLIDE 2

Bubble chamber: theory

  • In a superheated fluid, bubbles will

collapse unless they are large enough (rc) to overcome surface tension: must deposit Eth in a radius less than rc à Eth & Eth/rc = dE/dx threshold

  • Threshold based on theory of Seitz

(Phys. of Fluids I, 2 (1958)) For a given fluid: Classical Thermodynamics gives Eth, rc in terms of P, T

liquid pressure vapor pressure surface tension

2

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SLIDE 3

Neutron calibraZon event

Pressure & temperature à min energy, dE/dx threshold à sensiZve to nuclear recoils but not electron recoils

1950s-1970s

3

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SLIDE 4

Gamma/Beta Backgrounds

2 4 6 8 10 12

Threshold (keV)

10-12 10-11 10-10 10-9 10-8 10-7 10-6 10-5 10-4 10-3 10-2

Probability of Nucleation Gamma Rejection by Chamber

PICO-0.1 U Chicago COUPP-1L Queen's COUPP-4 PICO-2L PICO-60

C3F8 CF3I

Various PICO Detectors

4

Aim for this level for 1 year exposure

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SLIDE 5

Nuclear target

  • Big advantage of bubble

chambers is the ease of changing nuclear target (lot’s of candidate refrigerants)

  • Previously used CF3I

(I for SI sensiZvity, F for SD sensiZvity), now using C3F8 (focusing on SD sensiZvity, low mass)

5

  • A. L. Fitzpatrick, see also: 0908.2991, 1203.3542, 1211.2818, 1308.6288

Response funcZons , , , etc

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SLIDE 6

PICO Bubble chamber operaZon

Pressure expansion puts target fluid in superheated state

Buffer fluid (water) Hydraulic fluid Target fluid (CF3I/C3F8) to hydraulic controller Synthetic silica jar

Wait for parZcle interacZon to nucleate a bubble, recompress

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SLIDE 7

Cameras capture stereoscopic bubble images @ 100 fps (primary trigger)

AcousZc sensors & fast pressure transducer capture sound & pressure rise from bubble growth

50ms

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SLIDE 8

AcousZc discriminaZon of α’s

  • Clear acousZc signature of single

nuclear recoil (track < ~μm)

  • Sound emission peaks

at rbubble ≈ 10 μm

  • α track much larger (~40 μm)

à separate nucleaZon sites à α’s several Zmes louder

8

COUPP-4 CF3I Target

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SLIDE 9

The PICO program

  • PICO: merger of PICASSO

and COUPP collaboraZons

  • PICO-2L C3F8 (2014-17)
  • C. Amole et al.,
  • Phys. Rev. Le-. 114, 231302 (2015)
  • Phys. Rev. D 93, 061101 (2016)
  • PICO-60 CF3I (2013)
  • Phys. Rev. D 93, 061101 (2016)
  • PICO-60 C3F8 (2016-17)
  • Phys. Rev. Le-. 118, 251301 (2017)
  • PICO-40L (2017-18)
  • PICO-500 (future)

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PICO-2L PICO-60

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SLIDE 10

PICO-60 Cleaning

  • Every component touching the inner volume

was cleaned against MIL-STD-1246C level 50

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Post-FiltraZon ParZculate Size DistribuZon

<5µm <15µm <25µm <50µm <100µm

  • ---- Mil-Std 1246C level 100
  • ---- Mil-Std 1246C level 50 (Goal)
  • ---- Mil-Std 1246C level 25

* Filter Sample Normalized by Flow

Par8culate Size Bin

Par8cles/liter

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SLIDE 11

PICO-60 run with blinded acousZcs

  • Filled with 52 kg C3F8 in June, 2016

– Blind analysis on data from November 2016 and January 2017 1167-kg-days at 3.3 keV threshold

  • 106 bulk singles in WIMP search dataset

– Consistent with 222Rn decay rate

  • Expected Neutron Background

– 3 mulZple bubbles in the physics data – 3:1 mulZples to singles raZo from calibraZon and simulaZon – 0-3 bulk singles would be consistent with neutrons and no anomalous background

11

  • C. Amole et al., arXiv:1702.07666
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SLIDE 12

Amer Opening the Box

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No events in signal region!

AcousZc Parameter

  • C. Amole et al., arXiv:1702.07666

Radon chain alphas

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SLIDE 13

101 102 103

WIMP mass [GeV/c2]

10-41 10-40 10-39 10-38 10-37

SD WIMP-proton cross section [cm2]

PICO-60 C3F8

Spin-dependent Limits

13

  • C. Amole et al., arXiv:1702.07666

Factor of 17 improvement!

PICASSO IceCube SuperK

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SLIDE 14

Moving forward: PICO-40L

Eliminate buffer fluid

14

Thermal Gradient

Purpose of buffer liquid is to isolate the acZve liquid from the stainless parts Thermal gradient can ensure that target fluid near stainless parts is not acZve

PICO-60 PICO-40L

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SLIDE 15

Thermal Gradient

Summary

15

  • PICO bubble chambers at the 40L

scale are background-free

  • PICO dominates the search for spin-

dependent WIMP-proton coupling

  • PICO-40L: Design changes expected

to further improve bubble chamber stability and lower neutron background, deployment this year

  • Ton-scale PICO-500 in engineering

stage, goal: data taking in 2019 PICO-40L

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SLIDE 16
  • C. Amole, M. Besnier,
  • G. Caria, G. Giroux,
  • A. Kamaha, A. Noble
  • M. Ardid, M. Bou-Cabo, I. Felis

D.M. Asner, J. Hall

  • D. Baxter, C.E. Dahl, M. Jin,
  • J. Zhang
  • E. Behnke, H. Borsodi, O. Harris,
  • A. LeClair, I. Levine, E. Mann,
  • J. Wells
  • P. Bhattacharjee.
  • M. Das, S. Seth

S.J. Brice, D. Broemmelsiek, P.S. Cooper, M. Crisler, W.H. Lippincott, E. Ramberg, M.K. Ruschman, A. Sonnenschein J.I. Collar, A.E. Robinson

  • F. Debris, M. Fines-Neuschild,
  • F. Girard, C.M. Jackson,
  • M. Lafrenière, M. Laurin,

J.-P. Martin, A. Plante,

  • N. Starinski, V. Zacek
  • R. Filgas, I. Stekl
  • S. Fallows, C. Krauss,
  • P. Mitra
  • I. Lawson
  • D. Maurya, S. Priya
  • K. Clark
  • R. Neilson
  • E. Vázquez-Jáuregui
  • J. Farine, A. Le Blanc,
  • R. Podviyanuk, O. Scallon,
  • U. Wichoski
  • O. Harris

16

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SLIDE 17

BACKUP

17

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SLIDE 18

Long term

18

  • Coherent neutrino

background much lower for light target compared to Xe

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SLIDE 19

Nucleon Coupling Limits

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Limits on neutron vs proton spin-dependent coupling

See Tovey for details:

D.R. Tovey, et al., Phys. Le-. B 488, 17 (2000)

  • C. Amole et al., arXiv:1702.07666

LUX P a n d a X

  • I

I PICO-60 CF3I PICO-2L C3F8 PICO-60 C3F8

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SLIDE 20

Comparison to Collider

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  • C. Amole et al., arXiv:1702.07666