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test site ~300 m.w.e.

at at Fermilab Fermilab

1 liter (2 kg) Bubble Chamber In NuMI tunnel

COUPP

University of Chicago Indiana University, South Bend Fermilab

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• Multi ton chambers were built in the 50’s- 80’s.

4" 56('783)36&(*'6.(-9($:$3/$1/'()$%&')(6.8/'3" No liquid that has been tested seriously has failed to work as a bubble chamber liquid (Glaser, 1960).

• Most common: Hydrogen, Propane
• But also “Heavy Liquids”: Xe, Ne, CF3Br, CH3I, and CCl2F2.
• Good targets for both spin- dependent and spin-independent scattering.
• Possible to “swap” liquids to check suspicious signals.

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• Bubble nucleation depends on dE/dx, which is low for electrons, high

for nuclear recoils

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• Energy to make bubble must be deposited inside critical radius, which depends on vapor

pressure, chamber operating pressure and surface tension (Seitz, 1954).

• We adjust the temperature and pressure to make Rc large compared to a nuclear recoil

length (<100 nm at 10 keV) and small compared to electron recoils (>1 micron)

RC = 2

vapor

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~ 100 nm

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Two views of same bubble (cameras offset by 90˚):

Neutron and Gamma Calibrations

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• Alpha decay produces monoenergetic, low energy nuclear recoils.

For example, consider 210Po->206Pb:

206Pb

• E = 5.407 MeV

ER= 101 keV

• The recoiling nucleus will nucleate a bubble in any chamber that is sensitive to

the lower energy (~10 keV) recoils expected from WIMP scattering.

• The 238U and 232Th decay series include many alpha emitters, including radon

(222Rn) and its daughters.

• Radon is highly soluble in bubble chamber liquids.

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• SD(p)=3 pb

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Material Uranium [ppt]

Natural (GE-214) 42,000 (0.8 /cm2-day) Heraeus Suprasil synthetic (20 kg chamber) 21* Covalent T-6040 synthetic (60 kg chamber) < 100 Corning synthetic 260* Dynasil synthetic 226* Kvartzsteklo synthetic 17*

• St. Gobain Spectrosil

< 4.6*

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