# GGG

# Collaboration:

- Sezione INFN e Universita' di Pisa, Sezione INFN e Universita' di Bologna

Location of the experiment: INFN - Sezione di Pisa (Laboratori di San Piero a Grado)

National Responsible: Anna M. Nobili (University of Pisa)

1. Goal of the experiment

Development of a fast rotating differential accelerometer for testing the equivalence principle to 1 part in 1013 on Earth or to 1 part in 1017 inside a small satellite in low Earth orbit.

more on the experiment...

2. Activities during 2002

State of the art prior to INFN approval (in mid March 2003)

GGG has been funded by ASI (Agenzia Spaziale Italiana) and the national Ministry of University and Research MIUR. The main results achieved with such funding are the following:

- design, construction and operation of a differential accelerometer made of weakly coupled concentric, co-axial test cylinders with self-centering capability in super-critical rotation
- system stabilization and operation with natural differential period of 10 s and 2.5 Hz spin rate
- low frequency stability in the relative motion of the test cylinders of 1.5ˇ10-7 m (limited by number of bits in the electronics of the analog-to-digital converter)
- measured value of Q relevant to the measurement (with full system assembled) of 16450 (at 0.9 Hz)

Milestones 2003

Active stabilization of whirl motions at all natural frequencies of the system | 31-12-03
Reduction of the dynamic range of the relative motion of the test cylinders and amplification of ADC electronics so as to improve the resolution by 1 order of magnitude | 31-12-03
Low frequency stability in the relative motion of the test cylinders of 10-8 m (with 15 s natural differential period and 2-to-4 Hz spin rate) | 31-12-03
Measurement of the Q relevant to the measurement (to confirm and possibly improve previous result) | 31-12-03
Measurement of low frequency seismic noise and active reduction of this platform noise by 1 order of magnitude | 31-12-03

3. INFN contribution to the experiment in terms of manpower

Manpower: 13 researchers (7.2 FTE)

Budget for the Year 2003: 2% of the INFN-CSN2 budget for the Year 2003

4. Publications in refereed journals (year 2002): 1

5. Conference talks (year 2002): 5

6. Number of undergraduate and doctoral theses on the experiment: 8 "laurea" degree theses; 1 doctoral thesis in Physics (ongoing)

7. Leadership roles in the experiment

Anna M. Nobili, spokesperson

8. Innovative instruments

GGG is an innovative differential accelerometer because it allows the expected signal to be modulated at high frequency, with consequent significant reduction of "1/f" electronic and mechanical noise. This is possible by exploiting the physical principle of supercritical rotation.

9. Competing experiments

GGG aims to compete with torsion balance ground experiments (the best ones are those by the "Eöt-Wash" group at the University of Washington, USA, which have reached 10-12). At present GGG is still far behind the "Eöt-Wash" results. However, it is based on novel physical principles (already demonstrated) which make it suitable for use in space for a very high precision test of the equivalence principle. Instead, the torsion balance is not suitable for flight (it requires 1-g preferential direction); moreover, its best result (10-12) appears to be hard to improve on (it was first achieved by Braginsky and Panov in 1972).

10. International Committee which has reviewed the experiment

GG and its preliminary GGG prototype have been reviewed by the Fundamental Physics Advisory Group (FPAG) of ESA (European Space Agency).

GG (based on the existence of the GGG laboratory prototype) was selected by ASI as a candidate for a national small scientific space mission and funded for Phase A Study in 1998; it was also selected and funded by ASI for an advanced Phase A Study in 2000.