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# Development of a torsion balance facility and a search for temporal variations in the Newtonian gravitational constant

Panjwani, Hasnain (2012)
Ph.D. thesis, University of Birmingham.

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## Abstract

The torsion balance is one of the key pieces of apparatus used in experimental searches for weak forces. In the search for an understanding of a Unified Theory, physicists have suggested a number of signatures that are detectable in laboratory measurements. This thesis describes the development of a new torsion balance facility, relocated from the BIPM (Bureau International des Poids et Mesures) [1], which has excellent environmental stability and benefits from a new compact interferometric readout for measuring angular motion which has been characterised and installed onto the torsion balance. The interferometer has sensitivities of 5 $$\times$$ 10$$^{-11}$$ radians$$\char{cmti10}{0x2f}$$$$\sqrt{Hz}$$ between 10$$^{-1}$$ Hz and 10 Hz, an angular range of over $$\pm$$1$$^ \circ$$ and significantly reduces sensitivity to ground tilt. With the new facility the first experiment searching for temporal variations in the Newtonian gravitational constant has been undertaken with a null result for $$\delta$$$$\char{cmti10}{0x47}$$$$\char{cmti10}{0x2f}$$$$\char{cmti10}{0x47}$$$$_0$$ for both sidereal and half sidereal signals at magnitudes greater than 5$$\times$$10$$^{-6}$$. These results have been used to set an upper limit on some of the parameters within the Standard Model Extension framework [2]. The thesis also reports on the design and manufacture of prototype test masses with a high electron-spin density of approximately 10$$^{24}$$ and negligible external magnetic field $$\leq$$ 10$$^{-4}$$$$\char{cmr10}{0x54}$$. These test masses can be used within the facility to potentially make it sensitive enough to conduct future spin-coupling experiments.

Type of Work: Ph.D. thesis. Speake, Clive C. Colleges (2008 onwards) > College of Engineering & Physical Sciences Astrophysics and Space Research Group, School of Physics and Astronomy QB AstronomyQC PhysicsTS Manufactures University of Birmingham 3758
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