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

Panjwani, Hasnain (2012). Development of a torsion balance facility and a search for temporal variations in the Newtonian gravitational constant. University of Birmingham. Ph.D.

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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:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):