[Bubble] A buffer-free concept bubble chamber for PICO dark matter searches

[Jay Benesch]

Anything we can copy here?  Or is it a case of the needs driving groups 
to the same solution?

https://arxiv.org/abs/1905.07367

A buffer-free concept bubble chamber for PICO dark matter searches
Matthew Bressler, Peter Campion, V. Scott Cushman, Alexander Morrese, 
Johannes M. Wagner, Salvatore Zerbo, Russell Neilson, Mike Crisler, C. 
Eric Dahl
(Submitted on 17 May 2019)

     In this paper, we report on the successful operation at Drexel 
University of the PICO collaboration's first C3F8 buffer-free prototype 
fluorocarbon bubble chamber. Previous PICO bubble chambers have produced 
world-leading WIMP search results with fluorocarbon target fluids, 
separated from the steel bellows by a buffer layer of water. Surface 
tension effects at the jar walls and liquid-liquid interface lead to a 
class of background events which have nuclear-recoil-like acoustic 
signatures and thus contaminate the WIMP-like signal region in analysis. 
Thus new bubble chambers are to be constructed "right-side-up", meaning 
that the jar of C3F8 is above the bellows with no water inside the inner 
vessel. The Drexel Bubble Chamber (DBC), runs successfully at and below 
the nuclear recoil thresholds used by PICO for WIMP searches, including 
thresholds as low as 1.19 keV. We have demonstrated sensitivity to 137Cs 
gammas and spontaneous fission neutrons from 244Cm, and acoustic alpha 
discrimination is demonstrated to be possible although the observed rate 
of alpha decays is very low. Position reconstruction from stereoscopic 
imaging allows for basic analysis cuts for calibration data. The 
successful construction and operation of this prototype confirm the 
effectiveness of the right-side-up design, which will be used in future 
dark matter searches such as PICO-40L and PICO-500.

Subjects: 	Instrumentation and Detectors (physics.ins-det)
Cite as: 	arXiv:1905.07367 [physics.ins-det]
   	(or arXiv:1905.07367v1 [physics.ins-det] for this version)