1. The US Laser Interferometer Gravitational-wave Observatory
Status and Plans
Nergis Mavalvala Royal Astronomical Society, London February 14, 2003

2. Global network of detectors
GEO
VIRGO
LIGO
TAMA
AIGO
LIGO
Detection confidence
Source polarization
Sky location
LISA

3. LIGO WA 3 k m ( 1 s )
4 km
2 km LA
4 km

4. Coincidences between Sites
Two Sites – Three interferometers
Separation ~ 3020 km
Time window:    msec time of flight
Source triangulation: ~ arcminute directionality
Coincidence
Local coincidence - Hanford 2K and 4K ~ 1/day
Hanford / Livingston coincidence (uncorrelated) < 0.1/yr
GEO / TAMA coincidences further reduces the false signal rate
Amplitude discrimination with full- and half- length ifos at Hanford
Source polarization
Data (continuous time-frequency record)
Gravitational wave signal MB/sec
Total data recorded MB/sec
Gravitational Wave Signal Extraction
Signal from noise (noise analysis, vetoes, coincidences, etc)

5. Operations Principles
Interferometer performance
Integrate commissioning and data taking consistent with obtaining one year of integrated data at h = by end of 2006
Physics results from LIGO I
Initial upper limit results in early 2003
First search results in 2004
Reach LIGO I goals by 2007
Advanced LIGO
Advanced LIGO proposal is about to be submitted
International collaboration and broad LSC participation
Advanced LIGO installation should begin by 2007

6. LIGO Organization & Support
LIGO Laboratory
MIT + Caltech
~140 people
Director: Barry Barish
LIGO Science
Collaboration
44 member institutions
> 400 individuals
Spokesperson: Rai Weiss
U.S. National Science Foundation UK
Germany
Japan
Russia
India
Spain
Australia $
SCIENCE
Detector
R&D
DESIGN
CONSTRUCTION
OPERATION

7. Initial LIGO Sensitivity Goal
Strain sensitivity < 3x /Hz1/2 at 200 Hz
Displacement Noise
Seismic motion
Thermal Noise
Radiation Pressure
Sensing Noise
Photon Shot Noise
Residual Gas
Facilities limits much lower

8. Limiting Noise Sources: Seismic Noise
Motion of the earth few mm rms at low frequencies
Passive seismic isolation ‘stacks’
amplify at mechanical resonances
but get f-2 isolation per stage above 10 Hz

9. Limiting Noise Sources: Thermal Noise
Suspended mirror in equilibrium with 293 K heat bath a kBT of energy per mode
Fluctuation-dissipation theorem:
Dissipative system will experience thermally driven fluctuations of its mechanical modes:
Z(f) is impedance (loss)
Low mechanical loss (high Quality factor)
Suspension  no bends or ‘kinks’ in pendulum wire
Test mass  no material defects in fused silica
FRICTION

10. Limiting Noise Sources: Quantum Noise
Shot Noise
Uncertainty in number of photons detected a
Higher input power Pbs a need low optical losses
(Tunable) interferometer response  Tifo depends on light storage time of GW signal in the interferometer
Radiation Pressure Noise
Photons impart momentum to cavity mirrors Fluctuations in the number of photons a
Lower input power, Pbs
 Optimal input power for a chosen (fixed) Tifo
Shot noise:
Laser light is Poisson distributed  sigma_N = sqrt(N)
dE dt >= hbar  d(N hbar omega) >= hbar  dN dphi >= 1
Radiation Pressure noise:
Pressure fluctuations are anti-correlated between cavities

11. Power-recycled Interferometer
Optical resonance: requires test masses to be held in position to meter “Locking the interferometer”
end test mass
Light bounces back and forth along arms ~100 times  30 kW
Light is “recycled” ~50 times  300 W
input test mass
Laser + optical field conditioning
6W single mode
signal

13. Science Running Plan
Two “upper limit” runs S1 and S2 (at publishable early sensitivity) are interleaved with commissioning
S1 Aug-Sep duration: 2 weeks
S2 Feb-Apr duration: 8 weeks
Finish detector integration & design updates...
Engineering "shakedown" runs interspersed as needed
First “search” run S3 will begins late (duration: 6 months)
Search for astrophysical signals at high strain sensitivity with high coincidence duty factor

14. S1 Run Summary 23 August – 9 September (17 days)
GEO and TAMA (part time) ran simultaneously
LIGO observation time ("science-mode" data)
L hours (42%) (limited by daytime seismic noise)
H hours (58%)
H hours (73%)
3x hours (23%)
Analyses near completion & preprints in preparation
Binary inspiral search
Burst search
Stochastic background search
Periodic/pulsar search
Logging was very close to LLO

15. Strain Sensitivities During S1
H2 & H1 L1
3*10-21 Hz f ~300 Hz
Substantially
Equals level of best strain sensitivity of TAMA (data taking 7, during S1), but at lower frequency

16. Displacement Sensitivity (Science Run 1, Sept. 2002)

17. Expected upper limits for S1
Preliminary “upper limit” sensitivities as projected in October 2002
Stochastic backgrounds
Upper limit 0 < 30
Neutron star binary inspiral
Upper limit distance < 200 kpc
Periodic sources PSR J at 1283 Hz
Upper limit h < % CL
Actual refined analysis results to be presentation at AAAS meeting, 2003
S2 should be at least 10x more sensitive than S1

18. Search for gravitational waves from coalescing binaries
Three targets:
Neutron star binaries (1-3 Msun)
Black hole binaries (> 3 Msun)
MACHO binaries (0.5-1 Msun)
Search method
template based matched filtering
Status
Neutron star search complete
MACHO search under way
Black hole search in S2
Neutron star search
2.0 post-Newtonian template waveforms for non-spinning binaries
Discrete set of 2110 templates designed for at most 3% loss in SNR
Sensitivity measured in distance to 2 x 1.4 Msun optimally oriented inspiral at SNR = 8
40 kpc < D < 200 kpc
Sensitive to inspirals in
Milky Way, LMC & SMC

19. Analysis Pipeline Event Candidates IFO 1 Matched filter trigger:
If SNR > 6.5, compute a2 : small values indicate that SNR accumulates in manner consistent with an inspiral signal.
If a2 < 5.0, record trigger
Triggers are clustered within duration of each template
Auxiliary data triggers
Vetoes eliminate noisy data
GW Channel
Auxiliary Data
GW Channel
Matched
Filter
Auxiliary Data
Veto
IFO 2
DMT
Matched
Filter
DMT
Veto
Event Candidates
Coincident in time, binary mass, and distance when H1, L1 clean
Single IFO trigger when only H1 or L1 operate
Event Candidates

20. Strain Sensitivity coming into S2
6 Jan L1

21. The next-generation detector Advanced LIGO (aka LIGO II)
Now being designed by the LIGO Scientific Collaboration
Goal:
Quantum-noise-limited interferometer
Factor of ten increase in sensitivity
Factor of 1000 in event rate. One day > entire 2-year initial data run
Schedule:
Begin installation: 2007
Begin data run: 2009

22. A Quantum Limited Interferometer
Facility limits
Gravity gradients
Residual gas
(scattered light)
Advanced LIGO
Seismic noise 4010 Hz
Thermal noise 1/15
Optical noise 1/10
Beyond Adv LIGO
Thermal noise: cooling of test masses
Quantum noise: quantum non-demolition
LIGO I
LIGO II
Seismic
Suspension thermal
Test mass thermal
Quantum

23. Optimizing the optical response: Signal Tuning
Power
Recycling
Signal
r(l).e i f
(l) l
Cavity forms compound output coupler with complex reflectivity. Peak response tuned by changing position of SRM
Reflects GW photons back into interferometer to accrue more phase

24. Advance LIGO Sensitivity: Improved and Tunable
Thorne…
SQL  Heisenberg microscope analog
If photon measures TM’s position too well, it’s own angular momentum will become uncertain.

25. Conclusion
LIGO construction is complete, and the worldwide GW community is actively exploiting its scientific capabilities along with sister detectors GEO and TAMA
Despite setbacks, sensitivity has improved 4 decades in 2 years (though still another decade to go...)
We are analyzing S1 coincidence science data more sensitive than any prior search
S2 and S3 promise significantly better sensitivity and uptime
We are moving forward with our proposal for advanced next-generation detectors to increase search volume by a further factor of 1,000+ within this decade

26. Sensitivity to Stochastic Background

27. Implications for source detection
NS-NS Inpiral
Optimized detector response
NS-BH Merger
NS can be tidally disrupted by BH
Frequency of onset of tidal disruption depends on its radius and equation of state a broadband detector
BH-BH binaries
Merger phase  non-linear dynamics of highly curved space time a broadband detector
Supernovae
Stellar core collapse  neutron star birth
If NS born with slow spin period (< 10 msec) hydrodynamic instabilities a GWs
~10 min
~3 sec
20 Mpc
300 Mpc

28. Source detection Spinning neutron stars Stochastic background
Galactic pulsars: non-axisymmetry uncertain
Low mass X-ray binaries: If accretion spin-up balanced by GW spin- down, then X-ray luminosity  GW strength Does accretion induce non-axisymmetry?
Stochastic background
Can cross-correlate detectors (but antenna separation between WA, LA, Europe a dead band)
W(f ~ 100 Hz) = 3 x (standard inflation  10-15)
(primordial nucleosynthesis d 10-5)
(exotic string theories  10-5)
Signal strengths for
20 days of integration
Sco X-1
Thorne
GW energy / closure energy

29. Astrophysical sources of GWs
Coalescing compact binaries
Classes of objects: NS-NS, NS-BH, BH-BH
Physics regimes: Inspiral, merger, ringdown
Other periodic sources
Spinning neutron stars  numerically hard problem
Burst events
Supernovae  asymmetric collapse
Stochastic background
Primordial Big Bang (t = sec)
Continuum of sources
The Unexpected
GWs
neutrinos
photons
now
Coalescing compact binaries  chirp sources
NS-NS  far away; long periods; final inspiral gives GW chirp
NS-BH  tidal disruption of NS by BH; merger  GRB triggers
Inspiral  accurate predition with PPN proportional to (v/c)^11
Merger  nonlinear dynamics of highly curved spacetime
Ringdown  ringdown of modes of coalesced object
Periodic sources
Spinning NS  axisymmetry unknown
Galactic pulsars in SN remnant gases  non-axisymmetry unknown
LMXBs  mass accretion from companion
Is accretion spin-up balanced by GW spin-down?
Issues  axisymmetric distortion from radiation reaction force
Supernovae
Collapse  Dynamics not understood. If instability makes star into tumblong bar, then GWs
Core convection  detect via correlations with neutrinos