Experimental search for Gravitational Waves

Experimental search for Gravitational Waves
Geppo Cagnoli INFN - Firenze University of Glasgow Physik-Institut der Universität Zürich/ETH 28th June 2006

Gmn= 8pTmn The GR prediction Newton’s Theory
“instantaneous action at a distance” Gmn= 8pTmn Einstein’s Theory information carried by gravitational radiation at the speed of light 28th June 2006 Physik-Institut der Universität Zürich / ETH

Sources of Gravitational Waves
Small amplitude approximation Mass quadruple moment Compact object binaries Pulsars Neutron Star internal dynamics Non symmetrical supernovae Cosmological gravitational waves 28th June 2006 Physik-Institut der Universität Zürich / ETH

Physik-Institut der Universität Zürich / ETH
New potential sources January 05: A swarm of 10,000 or more black holes may be orbiting the Milky Way's supermassive black hole, according to new results from NASA's Chandra X-ray Observatory. This would represent the highest concentration of black holes anywhere in the Galaxy. 28th June 2006 Physik-Institut der Universität Zürich / ETH

Detection Principles -1
In the reference frame of the lab (Fermi’s coordinates) the effect of GW is pure mechanical. The potential is: 3 types of detectors Resonators Interferometers RF cavities Inertia Dimensions 28th June 2006 Physik-Institut der Universität Zürich / ETH

Effect of a sinusoidal gravitational wave going through the slide on the space-time frame and on a circular distribution of free masses Figure: M.Lorenzini DL L DL/L < Expected from astronomical sources 28th June 2006 Physik-Institut der Universität Zürich / ETH

Two detectors fully developed: Resonant Masses Interferometers Figure: S. Reid 28th June 2006 Physik-Institut der Universität Zürich / ETH

Theory of GW Detectors - 1
Read-out V h x f Readout internal noise Detector internal noise 28th June 2006 Physik-Institut der Universität Zürich / ETH

First attempt of building a resonant detector
Joseph Weber (~1960) Resonant bar suspended in the middle Sensitivity pattern Piezoelectric transducers 28th June 2006 Physik-Institut der Universität Zürich / ETH

The Band Width of a resonant detector
Detector noise x/h Read-out noise Detector BW 28th June 2006 Physik-Institut der Universität Zürich / ETH

Resonant detectors today
GW bursts excite the resonances of the test masses Spheres Bars mechanical signal enhancement Capacitive + SQUID or optical readout 28th June 2006 Physik-Institut der Universität Zürich / ETH

A capacitive Read-out system of a resonant detector
Bar SQUID Amplifier Matching Transformer Capacitive Resonant Transducer Decoupling Capacitor Charging Line L s i Cryogenic Switch M C T d 28th June 2006 Physik-Institut der Universität Zürich / ETH

28th June 2006 Physik-Institut der Universität Zürich / ETH

Interferometric detectors: the concept
Monitoring the distances between free-flying masses with laser interferometer The background noise comes from the readout and from the internal motion of the masses 28th June 2006 Physik-Institut der Universität Zürich / ETH

A bit of history… Gertsenshtein M E and Pustovoit V I Sov. Phys.—JETP Moss G E, Miller L R and Forward R L Appl. Opt b Weiss R Q. Prog. Rep. Res. Lab. Electron 28th June 2006 Physik-Institut der Universität Zürich / ETH

The Band Width of an interferometric detector
Detector noise x = h · L / for each end mirror Read-out noise Detector BW 28th June 2006 Physik-Institut der Universität Zürich / ETH

Interferometers today - 1
End mirrors positioned in the Dark Fringe condition: laser beam is frequency modulated, the sidebands are detected Multiple bouncing phase accumulation: laser power increases from 20W to 1kW Power recycling: number of photons in the interferometer increases Signal recycling: just the side bands are reflected back in the interferometer GEO600 is the only detector that uses this technique to enhance the detector response in a narrow band Pendulum suspensions Fabry – Perot cavities Beamsplitter Photodiode Laser 28th June 2006 Physik-Institut der Universität Zürich / ETH

Pendulum suspensions Fabry – Perot cavities Beamsplitter Photodiode Laser 28th June 2006 Physik-Institut der Universität Zürich / ETH

Pendulum suspensions Fabry – Perot cavities Beamsplitter The optics and suspensions are in vacuum to minimize fluctuation of index of refraction Photodiode Laser 28th June 2006 Physik-Institut der Universität Zürich / ETH

3 km 600 m TAMA 4 & 2 km 300 m AIGO 4 km 28th June 2006 Physik-Institut der Universität Zürich / ETH

Real data from LIGO 28th June 2006 Physik-Institut der Universität Zürich / ETH

Real data from GEO600 10 -17 Displacement [m] 10 -18 10 -19 100 1000 [Hz] 28th June 2006 Physik-Institut der Universität Zürich / ETH

Real data from Virgo 28th June 2006 Physik-Institut der Universität Zürich / ETH

Detectors of 1st Generation
1ST GENERATION IS CLOSE TO REACH THE DETECTION RANGE FOR NS-NS COALESCENCE AT THE DISTANCE OF THE VIRGO CLUSTER (17MPc) 1 10 100 1k 10k Frequency [Hz] GEO600 LIGO VIRGO 1ST GENERATION FOR INTERFEROMETERS STEEL SUSPENSIONS (APART GEO600) ROOM TEMPERATURE FOR RESONATORS Al or AlCu 100mK < T < 4K AURIGA NAUTILUS MiniGRAIL 10 -22 10 -23 10 -24 10 -25 10 -19 10 -20 10 -21 h NS-NS 14 Mpc BH-BH 67 Mpc Pulsars [ Hz –1/2 ] Supernovae NS vibration BUT THE EVENT RATE IS TOO LOW !! 1 EVENT/3 YRS MOST OPTIMISTIC CASE 28th June 2006 Physik-Institut der Universität Zürich / ETH

Future Detectors of Gravitational Waves
DUAL Nested hollow cylinder resonant detector AURIGA collaboration Construction planned starting on 2009 Ad. LIGO, Ad. Virgo and GEO HF 2nd generation interferometers Virgo + GEO600 collaboration Commissioning starts on 2009 3rd Generation Interferometer Cryogenic and underground interferometer Construction envisaged by 2014 28th June 2006 Physik-Institut der Universität Zürich / ETH

DUAL – the concept read-out the differential deformations of two nested resonators The outer resonator is driven above resonance The inner resonator is driven below resonance π Phase difference 5.0 kHz useful GW band 28th June 2006 Physik-Institut der Universität Zürich / ETH

DUAL performance Q/T=2x108 K-1 Mo Dual 16.4 ton height 3.0m 0.94m
M. Bonaldi et al. Phys. Rev. D (2003) Mo Dual ton height 3.0m m SiC Dual 62.2 ton height 3.0m m Antenna pattern: like 2 IFOs colocated and rotated by 45° Q/T=2x108 K-1 28th June 2006 Physik-Institut der Universität Zürich / ETH

Real data from Virgo EARTH RELATED NOISE THERMAL NOISE READOUT CONTROL RELATED NOISE 28th June 2006 Physik-Institut der Universität Zürich / ETH

Readout noise – shot noise
A fundamental limit to phase measurement is due to the quantum nature of light Phase measurements to a level of rad require about 1 MW of laser power in the optical cavities But more power = more fluctuating radiation pressure P=1 MW  F=3 mN  dF=1.5 DN · Dj ≥ 1/2 fN √Hz 28th June 2006 Physik-Institut der Universität Zürich / ETH

Readout noise The Standard Quantum Limit
For a simple Michelson interferometer (GEO HF parameters) Roman Schnabel MPG-AEI Hannover Radiation pressure noise SQL 10-21 Quantum limit on phase measurement Strain [ 1/√Hz ] Quantum noise with increased laser power (x100) 10-23 1 Frequency [ Hz ] 100 28th June 2006 Physik-Institut der Universität Zürich / ETH

Beyond the SQL: Squeezed Light
In one representation of the EM field the two orthogonal states are the Amplitude Quadrature X1 and the Phase Quadrature X2 Roman Schnabel MPG-AEI Hannover 28th June 2006 Physik-Institut der Universität Zürich / ETH

Beyond the SQL: Squeezed Light
10-21 Roman Schnabel MPG-AEI Hannover Quantum limit on phase measurement Strain [ 1/√Hz ] Noise reduction by squeezed light - 6 dB in variance Radiation pressure noise SQL 10-22 1 Frequency [ Hz ] 100 28th June 2006 Physik-Institut der Universität Zürich / ETH

Squeezed light demonstrations
[Vahlbruch et al., Phys. Rev. Lett., submitted (2005)]. [Chelkowski et al., Phys. Rev. A 71, (2005)]. 28th June 2006 Physik-Institut der Universität Zürich / ETH

Intermediate frequencies
From the realm of Quantum to the realm of Statistical Physics 10-19 10-25 Strain [ 1/√Hz ] THERMAL NOISE 1 10 k Frequency [ Hz ] 28th June 2006 Physik-Institut der Universität Zürich / ETH

Thermal noise Non isolated system shows uncorrelated fluctuations of volume and temperature The equipartition principle states that each observable has a mean energy equal to kBT/2 The observable Optical readout: part of the mirror sensed by the laser Capacitive readout: the average position of the capacitor plates 28th June 2006 Physik-Institut der Universität Zürich / ETH

Thermal noise reduction strategy
Linear systems & thermal equilibrium Each dynamic variable <E>= kT Fluctuation-Dissipation theorem Lower T  Lower thermal noise Thermal noise for Damped Harmonic Oscillator R.K.Patria Statistical Mechanics Pergamon Press Log f Noise Log [S xx (w) ] Lower dissipation  Lower thermal noise 28th June 2006 Physik-Institut der Universität Zürich / ETH

The most severe limit for IFOs: thermal noise from the coatings
Alternate layers of transparent materials with different index of refraction Impedance mismatch and interference produce high coefficient of reflectivity Its structure is not compact as the substrate Deposition with DIBS 10 mm of coating produces more thermal noise than 10 cm of substrate 1 10 k Frequency [ Hz ] 10-19 10-25 Strain [ 1/√Hz ] QUANTUM COATINGS EGO SUBSTRATES 28th June 2006 Physik-Institut der Universität Zürich / ETH

Suspensions at room temperature
Best material: silica (SiO2) Silicate bonding Tested on GEO600 28th June 2006 Physik-Institut der Universität Zürich / ETH

Silicon for mirrors and suspensions at low T
Thermal expansion null at 124K and 18K  main source of thermal noise is ruled out High thermal conductivity Monocrystal ingots up to 45cm diameter Possibility of monolithic suspensions Diffractive as well as transmissive interferometry allowed 5000 k 2.5e-6 a 28th June 2006 Physik-Institut der Universität Zürich / ETH

Earth related noise - 1 Test masses have to behave like free flying objects, yet they have to be suspended against gravity Seismic motion always present has to be filtered 28th June 2006 Physik-Institut der Universität Zürich / ETH

Earth related noise - 2: Isolation short-circuit
The Newtonian noise will be dominant below 10 Hz for cryogenic detectors Surface waves die exponentially with depth: GO UNDERGROUND! Newtonian noise SEISMIC NOISE Figure: M.Lorenzini 28th June 2006 Physik-Institut der Universität Zürich / ETH

Further considerations
Building the most perfect inertial reference system A system subjected to the quantum problem of measurement All the fundamental parameters of the detector have to be CONTROLLED without introducing a significant noise 28th June 2006 Physik-Institut der Universität Zürich / ETH

Detector Generations Distance Rate NS-NS 14 Mpc 1/30ce 1/3yr NS-BH 29 Mpc 1/25ce 1/2yr BH-BH 67 Mpc 1/6ce 3/yr 1 10 100 1k 10k Frequency [Hz] Ad VIRGO Mo DUAL SiC DUAL GEO600 LIGO VIRGO AURIGA NAUTILUS MiniGRAIL 3rd GENERATION INTERFEROMETER 10 -22 10 -23 10 -24 10 -25 10 -19 10 -20 10 -21 h [ Hz –1/2 ] NS-NS 240 Mpc 3/yr 4/day NS-BH 500 Mpc 1/yr 6/day BH-BH Z~0.3 1/month 30/day 28th June 2006 Physik-Institut der Universität Zürich / ETH

NS-NS coalescence range
BH-BH coalescence range NS-NS coalescence range GRB050509B 3RD GENERATION INTERFEROMETER 1ST GENERATION 2ND GENERATION 28th June 2006 Physik-Institut der Universität Zürich / ETH

Beyond Earth based detectors: LISA
Audio band 1 Hz – 10 kHz LISA 28th June 2006 Physik-Institut der Universität Zürich / ETH

A collaborative ESA NASA mission
Cluster of 3 S/C in heliocentric orbit Trailing the earth by 20° (50 Mio km) Equilateral triangle with 5 Mio km arms Inclined against ecliptic by 60° 28th June 2006 Physik-Institut der Universität Zürich / ETH

The spacecraft LISA needs a purely gravitational orbit Test masses have to be shielded from solar wind Capacitive sensing of the test masses Feedback loop to propulsion FEEP thrusters with micro-Newton thrust 28th June 2006 Physik-Institut der Universität Zürich / ETH

The Payload 28th June 2006 Physik-Institut der Universität Zürich / ETH

LISA technology demonstration
10-12 Torsion pendulum 10-13 Flight test 10-14 LISA 10-15 28th June 2006 Physik-Institut der Universität Zürich / ETH

LISA Path Finder Mission
Only one S/C with two test masses is needed Testing: Inertial sensor Charge management Thrusters Drag-free control Low frequency laser metrology 28th June 2006 Physik-Institut der Universität Zürich / ETH

LISA sensitivity curve
LISA will see all the compact white-dwarf and neutron-star binaries in the Galaxy. (Schutz) 1 - 4 3 2 Frequency (Hz) 9 8 Detection threshold 6 M o z = RXJ 4U wave amplitude h 10 5 -5 -10 -15 apparent magnitude (GW flux) + B H 28th June 2006 Physik-Institut der Universität Zürich / ETH

A new way to observe the Universe
Conclusions A new way to observe the Universe 28th June 2006 Physik-Institut der Universität Zürich / ETH

Experimental search for Gravitational Waves

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