GG (GG (““Galileo Galileo GalileiGalilei””))TowardsTowards a space test of the a space test of the EquivalenceEquivalence PrinciplePrinciple toto 1010--1818

Anna M Nobili Dipartimento di Fisica “E. Fermi” Università di Pisa & INFN, Pisa – Italia

DedicatedDedicated toto Paolo Paolo FarinellaFarinella10 10 yearsyears after after hishis deathdeath(Pisa 14(Pisa 14--16 16 JuneJune 2010)2010)

Thinking back of Paolo: the most difficult thoughtsThinking back of Paolo: the most difficult thoughts……....

Paolo loved space missions, but knew that they take a long a long time … while he did not have much.. We started by proposing a space experiment to measure G and somehow as a result of that I am still here today talking to you of how to test the Equivalence Principle in space with the GG experiment! (The last paper we shared on the subject was: “The orbit of a space laboratory for the measurement G”, AJ 1988)

..I cannot help thinking that maybe this is what he missed when he used to say as a joke:

“ ..everybody should have the right to one week per year in which to be looked after like a child!”

Full awareness of being bound to a very limited lifetime shaped his lifestyle, though he mostly kept it for himself, pretending to be a normally healthy person. Unfortunately, the few of us with whom he shared the truth were foolish enough not to take it seriously and provide him with the care that almost surely would have granted him some more years of life…

A A veryvery high high precisionprecision test of the test of the EquivalenceEquivalence PrinciplePrinciple: : RelevanceRelevance toto PhysicsPhysics and and CosmologyCosmology (I)(I)

• Experimental evidence of an EP violation would imply the existence of a new physical interaction in Nature and make it for a scientific revolution.

• A null experimental result (no violation) to very high precision would strongly suggest that gravity is so fundamentally different from the other forces that a radical rethinking will be necessary to accommodate it within the same theoretical framework as the Standard Model based on quantum field theory (something similar to the discovery of the fundamentally different nature of light after the null result of Michelson-Morley experiment…). The result would tightly constrain physical theories for decades to come.

A A veryvery high high precisionprecision test of the test of the EquivalenceEquivalence PrinciplePrinciple: : RelevanceRelevance toto PhysicsPhysics and and CosmologyCosmology (II)(II)

“…Napoleon, and other great men of his type, they were makers of empire.. but there is an order of men who get beyond that, they are not makers of empire but they are makers of Universe … their hands are not stained by the blood of any human being on Earth…..Ptolomymade a Universe which lasted 14 hundred years … Newton also made a Universe which has lasted 3 hundred years …Einstein made a Universe and I can’t tell you how long that will last….”

G.B. Shaw honoring Einstein London 1930

With “dark matter” and “dark energy” puzzles only about 5% of the mass of the Universe is undesrtood today… we definitely have a problem, which calls for large scale in situ measurements as well as fundamental tests…

State of the art in EP testing (I)State of the art in EP testing (I)

E. Fischbach et al.: “Reanalysis of the Eötvös Experiment” PRL 1986

(-0.2 2.8)x10-12Be Al

MaterialsSource massApparatusAuthors

(0.3 1.8)x10-13Be TiEarthRotating torsionbalance. 20’ modulation

Eöt-Wash, PRL 2008

10-12

(SEP 1.3x10-3)Earthlike/ Moonlike

SunRotating torsionbalance. 1hr to 36’modulation

Eöt-Wash, PRL 1999

(-1.9 2.5)x10-12Be Cu

Earth

Rotating torsionbalance. 1hr modulation

Eöt-Wash, PRD 1994

(-0.3 0.9)x10-12Al PtSunTorsion balance. 8TMs. Not rotating. 24hr modulation byEarth rotation

Braginsky & PanovJETP 1972

(1.31)x10-11

10-8 10-9

Al Au

Manycombinations

Sun

Earth

Torsion balance. Notrotating. 24hr modulation by Earthrotation

Torsion balance. Notrotating. No signalmodulation

Roll, Krotkov & DickeAnn. Phys. 1964

Eötvös et al. 1900collected in Ann. Phys. 1922

a a

36 yr

14 yr

MaterialsSource massApparatusAuthors

10-785Rb & 87Rb

EarthCold atoms droppingFray et al with T. Hänsch., PRL 2004

10-9g measurement with cold atoms (Cs)Peters, Chung & Chu, Nature 1999

a a

GGG laboratory prototype current sensitivity in the field of the Sun (by lock-in detection/synchronous demodulation, under favorable conditions of reduced diurnal tilt noise) : 4x10-9 (macroscopic, fast rotating differential accelerometer in the field of the Sun)

Target: 10-15

10-16 (10-17)

85Rb & 87Rb

EarthCold atoms droppingDimopoulos, Graham, Hogan, Kasevich, PRL 2007

State of the art in EP testing (II)State of the art in EP testing (II)

Ongoing

Differ by 2 neutrons only!!!

GG (GG (““Galileo Galileo GalileiGalilei) : the basic ) : the basic conceptual designconceptual design

spin orb EP signal modulated by the rotating capacitors in between the test cylinders at

spin orb diff with

..and NO signal attenuation because the system is NOT a forced oscillator!

GG is the only EP experiment ever to make high frequency signal modulation possible. The advantages are enormous and far reaching!

““Galileo Galileo GalileiGalilei (GG)(GG)”” Phase APhase A--2 Study Report2 Study Report

Phase A-2 Study (2009) funded by ASI conducted by TAS-I (Torino)

DFC based on GOCE expertise (for which TAS-I was prime contractor)

Full 3D GG experiment simulator

Many requirements based on GGG laboratory prototype experimental results

http://eotvos.dm.unipi.it/PA2

Science goal: test the Equivalence Principle in the field of the Earth to 10-17

Satellite, orbit and the VEGA launcher Satellite, orbit and the VEGA launcher

To fly in near circular near equatorial orbit

GG satellite in the bay of VEGA (Kourou launch site)

2.2 m~600 km altitude

Passive attitude stabilization by 1-axis rotation at 1 Hz

550 kg total mass (with 20% margin) of which ; 100kg launch adapter, 80 kg payload)

Drag Free Control around orbit frequency

To be operated from Italian station in Malindi (Kenya)

1 yr nominal mission duration (up to 3 yr)

1.6 m

GG satellite GG satellite

GG satellite with solar panels

2.2 m

GG “spinning top”

Satellite and payload (I)Satellite and payload (I)

Satellite and payload (II)Satellite and payload (II)

GG differential accelerometer (I)GG differential accelerometer (I)

NOTE: We do not fly a vacuum chamber (use venting to space instead..)

GG EP violation signal recoveryGG EP violation signal recovery

EP violation signal after demodulation (from 1Hz rotation)

Error budget (I)Error budget (I)

How it is built

Establish requirements

Implement Drag Free ControlHeritage from GOCE!

Run GG Simulator

Analyze time history of test masses relative displacements

Single out systematic effects and check their magnitude and signature

Note on Drag Free Control:

• FEEP thrusters developed for LISA-PathFinder + adapted to GG (=> GG spin frequency reduced to 1 Hz; surface of solar panels increased)

• Small ad-hoc optical spin sensor built in Torino capable of measuring spin frequency to 10-5

Error budget for 10Error budget for 10--1717 goal (II)goal (II)

A simulator in the lab: A simulator in the lab: ““GG on the Ground (GGG)GG on the Ground (GGG)””

GGG lab at INFN Pisa-San Piero a Grado

Same number of degrees of freedom; same dynamical properties; position of relative equilibrium of the test masses in the horizontal plane is NOT stabilized by local gravity (as it should be as a test of experiment in space…)

GGG sensitivity: major improvements (I)GGG sensitivity: major improvements (I)

FFT of relative displacements of GGG test cylinders in the horizontal, not rotating, plane of lab

GGG sensitivity: major improvements (II)GGG sensitivity: major improvements (II)

PSD of relative displacements of GGG test cylinders in the horizontal, not rotating, plane of lab

sGGGsGGG (suspended GGG) (suspended GGG) -- ASI funds (I)ASI funds (I)

New chamber has the right symmetry and has been designed to minimize disturbances on GGG experiment

sGGG will be suspended inside chamber by cardanic joint (not rotating) to reduce low frequency terrain tilts passively, in addition to active tilt control now in use (Note: active tilt control is limited by thermal effects on tilt sensor and requires good thermal stabilization to be effective)

An Experiment Simulator will be built by Thales Alenia Space-Italy for the new GGG, similarly to the Simulator built for the space experiment, to be compared with experimental measurements …

sGGGsGGG (suspended GGG) (suspended GGG) -- (II)(II)

Passive attenuation of low frequency terrain tilt noise (I)Passive attenuation of low frequency terrain tilt noise (I)

Cardanic suspension for low frequency attenuation in the plane (only 2 lamellae of 1 direction visible)

Passive attenuation of low frequency terrain tilt noise (II)Passive attenuation of low frequency terrain tilt noise (II)

Experimental set up

1 lamella of the 2 to be used for tilt attenuation in each direction of the horizontal plane suspends a 64 kg pendulum mass

The bar with the “top” tiltmeter is modulated at a frequency of choice (chosen where noise is low) to measure with another tiltmeter on the pendulum mass how much the modulated signal is attenuated. In air, with large thermal variations and local disturbances this is a good way to establish in a quantitative way the passive attenuation achievable.

Passive attenuation of low frequency terrain tilt noise (III)Passive attenuation of low frequency terrain tilt noise (III)

Passive attenuation of low frequency terrain tilt noise (IV)Passive attenuation of low frequency terrain tilt noise (IV)

Large diurnal effects are due to the tiltmeter thermal dependence; note that on the pendulum mass the nradlevel is achieved, which is the nominal sensitivity of the tiltmeter … BUT IS THIS THE TRUE HORIZONTAL LEVEL ??? Only a more sensitive instrument can telll …

Passive attenuation of low frequency terrain tilt noise (V)Passive attenuation of low frequency terrain tilt noise (V)

The modulated signal is attenuated by a factor 10000!!!

““OldOld”” GGG in new chamberGGG in new chamber

25 days continuous run of 25 days continuous run of ““oldold”” GGG rotor in new chamberGGG rotor in new chamber

25 days run started 13 Nov 2009 17:13 UTC, 3.6x105 spin period, 7.2x105 data points: except for a single jump, the rotating test cylinders (10 kg each, 0.167 Hz spin rate) never move away from each other by more than 0.4 microns (in the non rotating horizontal plane of the lab – X,Y axes along the lab walls)

With 2D sensitivity of GGG accelerometer it is like having 2 torsion balances oriented along 2 orthogonal directions of the horizontal plane of the lab

Lock in detection relative to the Sun shows that it can reach a sensitivity of about 70 pm

……then JPL got interested in GGthen JPL got interested in GG

…proposing to replace the GG capacitance read-out with a laser interferometry gauge developed by Mike Shao for SIM mission under many years of NASA funding and capable do detect 1 pm displacements in about 1 sec (very high sensitivity + differential)

Informal Workshop Pisa (Italy) 10-12 February 2010

http://eotvos.dm.unipi.it/Workshop2010/index.html

"Galileo Galilei" (GG) and GGG lab prototype: state of the art and new possibilities

Would such high sensitive read out allow GG to achieve an EP test to 10-18 ?

GG thermal noise revisitedGG thermal noise revisited

“Since in GG the signal is read at the rotation/modulation frequency of 1Hz, and the displacement thermal noise of the proof masses is inversely proportional to the square of the frequency at which displacement is modulated, thermal noise in GG is a factor 1 million smaller than in similar EP experiments where rotation frequencies are inevitably (by design) much smaller (10-3 Hz in other satellite experiments as well as in rotating torsion balances).

This explains why thermal noise of the LIGO and VIRGO mirrors at 100 Hz and above has values orders of magnitude below the picometer. In GG, by up-converting the frequency of an EP violation signal in the field of the Earth from its (low) orbital frequency of 1.7x10-4 Hz to the (high) rotation/modulation frequency of 1 Hz the highest ever in EP experiments proof mass thermal noise is reduced by orders of magnitude, as the ratio of these frequencies squared. Instead, cooling the experiment to superfluid He temperature would only reduce thermal noise by a factor 10.”

Quoting from the Workshop summary notes:

……GG: towards an EP test to 10GG: towards an EP test to 10--1818

A very low thermal noise allows the target signal to be detected in a much shorter integration time, results in a very high duty cycle and allows high precision differential measurements by the laser gauge to be fully exploited. We therefore plan to carry out a careful re-analysis of all systematic perturbations in GG so as to possibly aim at testing the EP one order of magnitude better than in the current error budget, i.e. to 10-18. The end-to-end GG simulator built at TAS-I in 2009 during GG Phase A-2 study is the crucial tool that allows this analysis to be performed in a reliable way and in a short time, at the very beginning of GG Phase B Study should ASI approve it … (analysis already started..)

JPL has just recently officially approached ASI in view of upcoming NASA Calls. (e.g. SALMON: Stand Alone Mission of Opportunity)

““Galileo Galileo GalileiGalilei (GG)(GG)””

GG Phase A-2 Study Reporthttp://eotvos.dm.unipi.it/PA2