RUI: Superheated Emulsions for the Detection of Dark Matter

Indiana University, Bloomington IN

Investigators

Abstract

One of the most enduring mysteries in astrophysics is the explanation for the compelling evidence that, on virtually all scales above the size of a star, far more gravitating material exists in an invisible form than that which can be detected by all known types of radiation. Generic extensions of the standard model of subatomic particles predict the existence of Weakly Interacting Massive Particles (WIMPS), which are excellent candidates for the dark matter. These are expected to interact very weakly with ordinary matter, and thus be extremely difficult to detect. The PICASSO group has undertaken the development of a new large dark matter detector derived from the well-known bubble chamber technique. In this application, the detector consists of a uniform emulsion of micron-sized halocarbon droplets suspended in a compliant material such as a polymeric or aqueous gel and kept in a superheated state (i.e., above their boiling point.) In this meta-stable state, the droplets can be vaporized by a nucleus recoiling from a collision with a WIMP. Sound emitted during this rapid phase transition can be recorded using acoustic sensors. The maturity of the technique, along with the ability to increase the target size at relatively low cost and the possibility of tailoring the response to specific types of radiation, have brought superheated emulsions to the forefront of dark matter investigations. PICASSO will be among the world's most sensitive detectors in the investigation of spin-dependent interactions between dark matter and WIMPs. The PI on this proposal at Indiana University, South Bend is responsible for sound sensors and their associated electronics, and for measuring acoustic properties of the detectors for PICASSO. The PI will also be responsible for measuring radon emanation from, and diffusion through, detector materials. The radioassay facility will also be available for use in other low background experiments. PICASSO will be sited at SNOLAB. Broader impacts: Enhancing the education of science majors and education majors is an integral part of this program. Three physics majors have participated in the work at Indiana University SB. They developed a data acquisition system, designed a device to couple to piezoelectric sensors in a unique fashion which is now being patented, and designed the transducer that will be used in the 2kg PICASSO detector. Education majors and local teachers will have inquiry-based science experiences and will produce written technical reports that they will defend orally at a collaboration meeting. Having participated in a real science project will inform the teaching of science when they are in the classroom. One secondary science education major is currently working with the PI and has produced 75 of the required 300 transducers for the 2 kg experiment and has helped to develop a rapid-cycling environment chamber for transducer testing.