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Development of a test of Newton's law of gravitation at micrometer distances using a superconducting spherical torsion balance

Rocco, Emanuele (2008)
Ph.D. thesis, University of Birmingham.

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Many theories associated with quantum gravity, such as string theory, predict violations of inverse square law (ISL) of gravity at sub millimetre distances. To search for such experimental signatures we developed a magnetically levitated cryogenic torsion balance, the SSTB, and a set of masses with modulated density across their surfaces. The lateral force has to be measured as one mass is moved in front of the other with a micropositioner without any electrostatic shield between them. The expected Newtonian and electromagnetic forces have been studied to optimise the design of the masses. The torque sensitivity of the SSTB has been modelled and its performances at 4.2 K discussed. A torque sensitivity of 2×10\(^{−10}\) Nm/√(Hz) at 30 mHz has been measured, most probably due to coupling with ground tilt. Two tests with prototypes of the masses has been performed. During the first test a torque due to electrostatic and magnetic forces of 8.4×10\(^{−11}\)±1.5×10\(^{−11}\) Nm has been measured at a mass spacing of 42±14μm at the spatial periodicity of the density modulation. During the second test by using improved masses the detected signal was reduced to 1.91×10\(^{−11}\)±4.7×10\(^{−12}\) Nm at a spacing of 30±10 μm. To look for violations of the ISL of gravity the torque sensitivity of the SSTB has to be further enhanced.

Type of Work:Ph.D. thesis.
Supervisor(s):Speake, Clive C.
School/Faculty:Schools (1998 to 2008) > School of Physics & Astronomy
Department:Centre for Space and Gravity Research
Keywords:experimental gravity, test of Newton's laws, test of gravity at micrometer distances, measurement of weak forces, test of inverse square law of gravity, superconducting torsion balance, experimental test of extension to the standard model, modeling of sensitivity of instrument for precision measurement of forces, design and construction of test masses for experimental gravity
Subjects:QC Physics
Institution:University of Birmingham
Library Catalogue:Check for printed version of this thesis
ID Code:1482
This unpublished thesis/dissertation is copyright of the author and/or third parties. The intellectual property rights of the author or third parties in respect of this work are as defined by The Copyright Designs and Patents Act 1988 or as modified by any successor legislation. Any use made of information contained in this thesis/dissertation must be in accordance with that legislation and must be properly acknowledged. Further distribution or reproduction in any format is prohibited without the permission of the copyright holder.
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