1. Fundamental Physics. May 3rd 2006 1 Clive Speake G.Hammond, A. Matthews, F.Pena, S. Aston, E.Rocco. Gravitation Group, University of Birmingham. Motivation Brief overview of laboratory tests of gravitation Work at University of Birmingham Summary Precision tests of gravity: Particle physics at the low energy Frontier.

2. Fundamental Physics. May 3rd 2006 2 Motivation Standard Model of Particle Physics successfully describes Electro-weak and Strong interactions up to ~10 2 GeV. Standard Model of Cosmology (founded on classical General Relativity) successfully ‘explains’ observations of the Universe from a second or so after ‘Big-Bang’. BUT...

3. Fundamental Physics. May 3rd 2006 3 But... Gravitation cannot be renormalised like the other quantum interactions as there is no m f in nature. The natural scale for a quantum theory of gravity is the Planck scale: M p c 2 ~10 19 GeV. What happens between the Electro-Weak scale and the Planck scale (16 orders of energy)? Hierarchy problem. We need new symmetries eg Supersymmetry, Peccei-Quinn symmetry, but we have no direct evidence for these. Cosmology needs Dark Matter but we have not observed it yet. We require the majority of the mass/energy density of the Universe to consist of a zero-point fluctuation vacuum energy: Dark Energy.

4. Fundamental Physics. May 3rd 2006 4 Motivation Recent attempts at solving these problems suggest the possibility of new macroscopic forces. New gauge symmetries and conserved quantities lead to new forces eg axion, new forces coupling to conserved charges B, B-L. String theories predict a number of phenomena: macroscopic compactified dimensions, dilaton, moduli and others...

5. Fundamental Physics. May 3rd 2006 5 T Generic form of new interactions Assume a Yukawa-type potential: with  mm for m b c 2 ~0.2 meV

6. Fundamental Physics. May 3rd 2006 6 Adapted From Smith and Lewin 1990. weak Force Physics

7. Fundamental Physics. May 3rd 2006 7 Tests of gravitation Equivalence Principle. Searches for G-dot. Macroscopic forces coupling to intrinsic spin: search for axion-like particles, search for cosmic spin fields, breakdown of Lorentz invariance. Inverse square law/ Casimir force. For a review see Gundlach New J. Phys. 7 205 (2005)

8. Fundamental Physics. May 3rd 2006 8 Superconducting Torsion Balance Cavendish Balance (1798-Present) Birmingham Instrument in Casimir mode (1998-Present)  Based on Meissner effect zero stiffness suspension utilising Niobium  Temperature of 4.2K  Lift capacity  600g  Superconducting magnetic torque feedback.  We will eventually utilise a novel homodyne interferometric readout  MkI Noise  10 -13 Nm/  Hz Rev. Sci. Instrum. 75, 955 (2004)

9. Fundamental Physics. May 3rd 2006 9 The Spherical Superconducting Torsion Balance: Levitation Bearing Float Cryogenic analogue of a spherical air-bearing Copper shell 0.2mm, coated with Pb, (Nb). Hard drawn Nb wire.

10. Fundamental Physics. May 3rd 2006 10 Piezo Sphere -Plane Float Interferometer Spark eroded Nb foil feedback coils

11. Fundamental Physics. May 3rd 2006 11 Interferometer development for SSTB

12. Fundamental Physics. May 3rd 2006 12 Birmingham interferometer for LISA: Schematic of first prototype. C&QG 2005 A1,2 Polarising Beamsplitter B /4 Plate C Non-Polarising Beamsplitter D  Plate PD1,2,3 Photodiode P Polariser L1,2,3 Lens Laser Diode A1 B C B A2 P D PD1 PD2PD3 Proof Mass Reference Mirror L3L2 L1 Main beamsplitter Cat’s eye A2

13. Fundamental Physics. May 3rd 2006 13 Birmingham Interferometer: First prototype (40x70x25mm).

14. Fundamental Physics. May 3rd 2006 14 Birmingham interferometer: Performance. Using a 664nm VCSEL with 60 nW of optical power on diodes. Shot noise limited above 20 Hz. Nominally equal optical path lengths.

15. Fundamental Physics. May 3rd 2006 15 Casimir’s Calculation Zero-point energy of modes between plates of dimension L: z x d

16. Fundamental Physics. May 3rd 2006 16 Shortcomings of Casimir’s analysis Thermal Correction When, corresponding to d=7  m at room temperature,. thermal photons contribute to Casimir force. How to model conductivity of real metals? Roughness correction Electrostatic forces due to patch-potentials.

17. Fundamental Physics. May 3rd 2006 17 Conductivity, roughness, thin film and patch-potential corrections are minimised by using larger spacings between conductors. But force is smaller! The controversial thermal correction is minimised at larger separations at 4K. Plasmons have larger effect at shorter spacing? Reynaud and Lambrecht et al 2001

18. Fundamental Physics. May 3rd 2006 18 Birmingham work Assuming sensitivity of Mk1 device (Hammond et al 2004), we can resolve 0.5% of Casimir force at 4  m in 1 hour (R=10cm). Aim at ‘precision’ determination of Casimir force 0.1%. Crucial to damp parasitic modes of oscillation: – horizontal and vertical translational modes damped using copper-cored inductor in series with levitation bearing. –Simple pendulum mode damped using copper disk attached to the inside of float at its pole with superconducting electromagnet.

19. Fundamental Physics. May 3rd 2006 19 Experimental Tests of Newton’s law University of Washington Currently testing Newtonian gravity at 150  m. Aiming at 50  m. Employ conducting membrane as electrostatic shield between source and test mass. Eot-wash website Source mass Test mass Optical lever Torsion fibre

20. Fundamental Physics. May 3rd 2006 20 Birmingham work in progress Push to shorter ranges by dispensing with the electrostatic shield. Use transverse geometry to eliminate forces due to long and short range electrostatic interactions and Casimir force Exploit novel features of Spherical Superconducting torsion balance being developed at University of Birmingham.

21. Fundamental Physics. May 3rd 2006 21 Long range stick-slip piezo Modulated masses Test of the inverse square law: Basic concept Centre of simple pendulum motion coincides with centre of buoyancy.

22. Fundamental Physics. May 3rd 2006 22 Source/Test mass manufacture at RAL Al mandrill 150  m deep 400  m pitch, 50% fill.

23. Fundamental Physics. May 3rd 2006 23 Source/Test mass manufacture at RAL Electroplate with Au. Cover Al relief.

24. Fundamental Physics. May 3rd 2006 24 Source/Test mass manufacture at RAL Skim off the top layer to uncover Al.

25. Fundamental Physics. May 3rd 2006 25 Source/Test mass manufacture at RAL Sputter coat Au to thickness of 3  m

26. Fundamental Physics. May 3rd 2006 26 Source/Test mass manufacture at RAL Dissolve Al mandrill.

27. Fundamental Physics. May 3rd 2006 27 Al mandrill Au plating prior to skimming Courtesy of Peter Huggard, RAL.

28. Fundamental Physics. May 3rd 2006 28 Current Status We have completed development of Mk2 SSTB with capacitative angular readout. Current sensitivity is limited by capacitive sensor noise. This can be improved. Completion of cryogenic interferometer is due in 2-3 months.

29. Fundamental Physics. May 3rd 2006 29 Parametrisation of violation of inverse square law

30. Fundamental Physics. May 3rd 2006 30 moduli Dilaton RadionVacuum energy scenario 2 compact extra dimensions Possible signals

31. Fundamental Physics. May 3rd 2006 31 Potential upper limits

32. Fundamental Physics. May 3rd 2006 32 Summary Ideas beyond the Standard Model of Particle physics and, perhaps, also that of Cosmology are needed to make sense of gravity. Searches for new weak interactions are complementary to direct searches for new bosons in particle accelerators. Fundamental physics experiments in the lab or, perhaps, space can contribute.

33. Fundamental Physics. May 3rd 2006 33 Acknowledgements PPARC EPSRC BAE Leverhulme