LIGO The Search for Gravitational Waves

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LIGO The Search for Gravitational Waves

• Barry Barish
• Laboratori Nazionali del Gran Sasso
• 28-Oct-02

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Einsteins Theory of Gravitation gravitational
waves
Newtons Theory instantaneous action at a
distance Einsteins Theory information carried
by gravitational radiation at the speed of light

• A necessary consequence of Special Relativity
  with its finite speed for information transfer
• Time dependent gravitational fields come from
  the acceleration of masses and propagate away
  from their sources as a space-time warpage at the
  speed of light

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Direct Detectionastrophysical sources
Gravitational Wave Astrophysical Source
Terrestrial detectors LIGO, TAMA, Virgo,AIGO
Detectors in space LISA
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Astrophysics Sourcesfrequency range
Audio band

• EM waves are studied over 20 orders of
  magnitude
• (ULF radio -gt HE ?-rays)
• Gravitational Waves over 10 orders of magnitude
• (terrestrial space)

Space
Terrestrial
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Astrophysical Sources the search for
gravitational waves

• Compact binary inspiral chirps
• NS-NS waveforms are well described
• BH-BH need better waveforms
• search technique matched templates
• Supernovae / GRBs bursts
• burst signals in coincidence with signals in
  electromagnetic radiation
• prompt alarm ( one hour) with neutrino detectors
• Pulsars in our galaxy periodic
• search for observed neutron stars (frequency,
  doppler shift)
• all sky search (computing challenge)
• r-modes
• Cosmological Signalsstochastic background

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Interferometers terrestrial
free masses
free masses
International network (LIGO, Virgo, GEO, TAMA,
AIGO) of suspended mass Michelson-type
interferometers on earths surface detect distant
astrophysical sources
suspended test masses
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Suspended Mass Interferometerthe concept

• An interferometric gravitational wave detector
• A laser is used to measure the relative lengths
  of two orthogonal cavities (or arms)

• Arms in LIGO are 4km
• Current technology then allows one to measure h
  dL/L 10-21 which turns out to be an
  interesting target

causing the interference pattern to change at
the photodiode
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How Small is 10-18 Meter?
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What Limits Sensitivityof Interferometers?

• Seismic noise vibration limit at low
  frequencies
• Atomic vibrations (Thermal Noise) inside
  components limit at mid frequencies
• Quantum nature of light (Shot Noise) limits at
  high frequencies
• Myriad details of the lasers, electronics, etc.,
  can make problems above these levels

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Noise Floor40 m prototype
sensitivity demonstration

• displacement sensitivity
• in 40 m prototype.
• comparison to predicted contributions from
  various noise sources

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LIGO Observatories
Hanford Observatory
Livingston Observatory
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Coincidences between Sites

• Time Window
• Separation 3020 km (?? ? ??? msec)
• Two Sites Three interferometers
• Single interferometer non-gaussian
  level 50/hour
• Local coincidence - Hanford 2K and 4K
  (1000) 1/day
• Hanford/Livingston coincidence (uncorrelated) lt0.1
  /yr
• GEO / TAMA coincidences further reduces the false
  signal rate
• Data (continuous time-frequency record)
• Gravitational wave signal 0.2MB/sec
• Total data recorded 9 MB/sec
• Gravitational Wave Signal Extraction
• Signal from noise (noise analysis, vetoes,
  coincidences, etc)

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LIGO Scientific Collaboration
Oct 02
LSC Institutional Membership 44 collaborating
groups gt 400 collaborators
International India, Russia, Germany, U.K,
Japan, Spain and Australia.

• University of Adelaide ACIGA
• Australian National University ACIGA
• Balearic Islands University - Spain
• California State Dominquez Hills
• Caltech CACR
• Caltech LIGO
• Caltech Experimental Gravitation CEGG
• Caltech Theory CART
• University of Cardiff UK GEO
• Carleton College
• Cornell University
• Fermi National Laboratory
• University of Florida _at_ Gainesville
• Glasgow University GEO
• NASA-Goddard Spaceflight Center
• University of Hannover GEO
• Hobart Williams University
• India-IUCAA
• IAP Nizhny Novgorod

• LIGO Livingston LIGOLA
• LIGO Hanford LIGOWA
• Loyola New Orleans
• Louisiana State University
• Louisiana Tech University
• MIT LIGO
• Max Planck (Garching) GEO
• Max Planck (Potsdam) GEO
• University of Michigan
• Moscow State University
• NAOJ - TAMA
• Northwestern University
• University of Oregon
• Pennsylvania State University
• Southeastern Louisiana University
• Southern University
• Stanford University

The international partners are involved in all
aspects of the LIGO research program.
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LIGOschedule and plan
Primary Activities

• 1996 Construction Underway (mostly civil)
• 1997 Facility Construction (vacuum system)
• 1998 Interferometer Construction (complete
  facilities)
• 1999 Construction Complete (interferometers in
  vacuum)
• 2000 Detector Installation (commissioning
  subsystems)
• 2001 Commission Interferometers (first
  coincidences)
• 2002 Sensitivity studies (initiate LIGO I
  Science Run)
• 2003 LIGO I data run (one year integrated
  data at h 10-21)
• 2006 Begin Advanced LIGO installation

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LIGO Livingston Observatory
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LIGO Hanford Observatory
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Beam Pipe and Enclosure

• Minimal Enclosure (no services)
• Beam Pipe
• 1.2m diam 3 mm stainless
• 65 ft spiral weld sections
• 50 km of weld (NO LEAKS!)

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Vacuum Chambers and Seismic Isolation
Constrained Layer Damped Springs
Vacuum Chambers
Vacuum Chamber
Gate Valve
Passive Isolation
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LIGO I Suspension and Optics
fused silica
Single suspension 0.31mm music wire
Surface figure ?/6000

• surface uniformity lt 1nm rms
• scatter lt 50 ppm
• absorption lt 2 ppm
• internal Qs gt 2 106

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Commissioning LIGO Subsystems
stabilization
10-4 Hz/Hz1/2
10-7 Hz/Hz1/2
10-1 Hz/Hz1/2
LIGO I Goal
NdYag 1.064 mm Output power gt8 Watt TEM00 mode
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LIGO Prestabilized Laser data vs simulation
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Interferometer Configuration
end test mass
Requires test masses to be held in position to
10-10-10-13 meter Locking the interferometer
Light bounces back and forth along arms about 150
times
Light is recycled about 50 times
input test mass
Laser
signal
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LIGO Facility Noise Levels

• Fundamental Noise Sources
• Seismic at low frequencies
• Thermal at mid frequencies
• Shot at high frequencies
• Facility Noise Sources (example)
• Residual Gas
• 10-6 torr H2 unbaked
• 10-9 torr H2 baked

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Lock Acquisition
Developed by Matt Evans Caltech PhD Thesis
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LIGO watching the interferometer lock
Y Arm
Laser
X Arm
signal
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LIGO watching the interferometer lock
X arm
Y arm
Y Arm
Anti-symmetricport
Reflected light
Laser
X Arm
signal
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Detecting the Earth Tides Sun and Moon
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LIGO Lab Planning Memo August 2001

• The LIGO Laboratory will carry out the E7 run
  before the end of the year. We anticipate that
  the run will take place during December and will
  be scheduled for two full weeks. The run is an
  engineering run and will be the responsibility of
  the LIGO Laboratory
• PRIMARY GOAL
• Establish coincidence running between the sites
• Obtain first data sample for shaking down data
  analysis

Last LIGO Construction Project Milestone
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LIGO GEO InterferometersE7 Engineering Run
28 Dec 2001 - 14 Jan 2002 (402 hr)
Coincidence Data All
segments Segments gt15min 2X H2, L1 locked
160hrs (39) 99hrs
(24) clean 113hrs (26)
70hrs (16) H2,L1 longest clean segment 150 3X
L1H1 H2 locked 140hrs (35)
72hrs (18) clean 93hrs (21)
46hrs (11) L1H1 H2 longest clean
segment 118 4X L1H1 H2 GEO 77 hrs
(23 ) 26.1 hrs (7.81 ) 5X ALLEGRO

• Singles data
• All segments Segments gt15min
• L1 locked 284hrs (71) 249hrs
  (62)
• L1 clean 265hrs (61) 231hrs
  (53)
• L1 longest clean segment 358
• H1 locked 294hrs (72) 231hrs
  (57)
• H1 clean 267hrs (62) 206hrs
  (48)
• H1 longest clean segment 404
• H2 locked 214hrs (53) 157hrs
  (39)
• H2 clean 162hrs (38) 125hrs
  (28)
• H2 longest clean segment 724

Conclusion Large Duty Cycle is Attainable
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LIGO Engineering Run (E7) Sensitivities
Final LIGO Milestone ----------- Coincidences Bet
ween the Sites in 2001 Engineering Run 28 Dec
01 to 14 Jan 02
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(No Transcript)
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Improvements to LHO 4k noise
S1
Further low-freq improvement 2 days later
13 Oct
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Science Runningplan

• Two upper limit runs S1 and S2, interleaved
  with commissioning at publishable early
  sensitivity
• S1 Sept 02 duration 2 weeks
• S2 March 03 duration 8 weeks
  sensitivity better by gtx10
• First search run S3 will be performed in late
  2003 ( 6 months)

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LIGO data vs. SimLIGO
Triple Strain Spectra - Thu Aug 15 2002
LIGO S1 Run ----------- First Upper Limit
Run Aug Sept 02
Strain (1/Hz1/2)
Frequency (Hz)
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Preliminary
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S1 Duty Cycle

LLO-4K LHO-4K LHO-2K All three together
Integrated lock time (gt300 sec per segment) 169 hours 232 hours 288 hours 96 hours
Duty cycle (cf. 400 hour run time) 43 59 73 24

• Longest locked section for individual
  interferometer 21 hrs (11 in Science
  mode)
• Need to improve low frequency seismic isolation
  protection from local
  anthropogenic noise

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Upper LimitsS1,S2 Data Analysis Groups

• Compact binary inspiral chirps
• Supernovae / GRBs bursts
• Pulsars in our galaxy periodic
• Cosmological Signal stochastic background

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Do Supernovae Produce Gravitational Waves?

• Not if stellar core collapses symmetrically (like
  spiraling football)
• Strong waves if end-over-end rotation in collapse
• Increasing evidence for non-symmetry from
  speeding final neutron stars
• Gravitational wave amplitudes uncertain by
  factors of 1,000s !!

Puppis A
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Explosion of a Star supernova sequence
gravitational waves
ns
light
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Model of Core Collapse Burrows et al
kick sequence
gravitational core collapse
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Supernovae gravitational waves
Non axisymmetric collapse
burst signal
Rate 1/50 yr - our galaxy 3/yr - Virgo cluster
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Supernovae asymmetric collapse?

• pulsar proper motions
• Velocities -
• young SNR(pulsars?)
• gt 500 km/sec

• Burrows et al
• recoil velocity of matter and neutrinos

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Supernovaesignatures and sensitivity
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Upper LimitsS1,S2 Data Analysis Groups

• LSC Upper Limit Analysis Groups
• Typically 25 physicists
• One experimentalist / One theorist co-lead each
  group
• ----------------------------------
• Compact binary inspiral chirps
• Supernovae / GRBs bursts
• Pulsars in our galaxy periodic
• Cosmological Signal stochastic background

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Stochastic Background Sensitivity

• Detection
• Cross correlate Hanford and Livingston
  Interferometers
• Good Sensitivity
• GW wavelength ? 2x detector baseline? f ? 40 Hz
• Initial LIGO Sensitivity ? ? 10-5
• Advanced LIGO Sensitivity ? ? 5 10-9

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Stochastic Background LHO/LLO coherence plots
from E7
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S1 Expected Sensitivities
Upper limit (90 CL, 70 hrs H2-L1 data) ?0 lt 30
40 Hz lt f lt 215 Hz NOTE Factor of 2 x 103
improvement over E7.
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Stochastic Background sensitivities
S1
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Advanced LIGO sensitivity and source signals

• Advanced LIGO 2.5 hours 1 year of Initial
  LIGO
• Volume of sources grows with cube of sensitivity
• 15x in sensitivity 3000 in rate

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Conclusions

• LIGO construction complete
• LIGO commissioning and testing on track
• Engineering test runs underway, during period
  when emphasis is on commissioning, detector
  sensitivity and reliability. (Short upper limit
  data runs interleaved)
• First Science Search Run first search run
  begin in 2003
• Significant improvements in sensitivity
  anticipated to begin about 2007
• Detection is likely within the next decade !

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Recent Improvements
The 4k interferometer is operating again with the
common mode servo engaged. Attached is a new
noise spectrum, compared with the previous best
of 15 Aug 02.   There is a factor of
5-10 improvement over most of the 20-200 Hz band.
We have not increased the anti-symmetric port
light from the acquisition level for this
spectrum, so the noise is a little higher at high
frequencies compared to the previous.  
Minimum strain noise is 7 10-21 /Hz1/2 over the
band 150-850 Hz.   The main new items
implemented since S1 are   o
optical lever whitening filters on the four test
masses o more filtering of the MC2
DAC output signal o dewhitening
filters on the BS and RM