View
217
Download
0
Category
Preview:
Citation preview
First Results from LIGO
Keith Riles University of Michigan
High Energy Physics Seminar
Michigan State University – Feb. 24, 2004
K. Riles - First Results from LIGO -2/24/04
2
Outline
Nature & Generation of Gravitational Waves
Interferometric Gravitational Wave Detection
The Initial LIGO Detector
The LIGO Scientific Collaboration
Science Run S1: Sensitivity & Data Quality
First analysis results and future prospects
Preparing for Advanced LIGO
K. Riles - First Results from LIGO -2/24/04
3
Gravitational Waves = “Ripples in space-time”
Perturbation propagation similar to light (obeys same wave equation!) Propagation speed = c Two transverse polarizations - quadrupolar: + and x
Amplitude parameterized by (tiny) dimensionless strain h: L ~ h(t) x L
Nature of Gravitational Waves
Example:
Ring of test masses
responding to wave
propagating along z
K. Riles - First Results from LIGO -2/24/04
4
Why look for Gravitational Radiation?
Because it’s there! (presumably)
Test General Relativity: Quadrupolar radiation? Travels at speed of light? Unique probe of strong-field gravity
Gain different view of Universe: Sources cannot be obscured by dust Detectable sources some of the most interesting,
least understood in the Universe Opens up entirely new non-electromagnetic spectrum
K. Riles - First Results from LIGO -2/24/04
5
What will the sky look like?
K. Riles - First Results from LIGO -2/24/04
6
Generation of Gravitational Waves
Radiation generated by quadrupolar mass movements:
(with I = quadrupole tensor, r = source distance)
Example: Pair of 1.4 Msolar neutron stars in circular orbit of radius 20 km (imminent coalescence) at orbital frequency 400 Hz gives 800 Hz radiation of amplitude:
K. Riles - First Results from LIGO -2/24/04
7
Generation of Gravitational Waves
Major expected sources in 10-1000 Hz band:
Coalescences of binary compact star systems
(NS-NS, NS-BH, BH-BH)
Supernovae
(requires asymmetry in explosion)
Spinning neutron stars, e.g., pulsars
(requires axial asymmetry or wobbling spin axis)
Also expected (but probably exceedingly weak):
Stochastic background – Big Bang remnant
K. Riles - First Results from LIGO -2/24/04
8
Generation of Gravitational Waves
Sources well below LIGO bandwidth: Binaries well before coalescence Inspiral of stars into massive black holes Coalescence of massive black holes Stochastic background (e.g, big bang remnant, superposition of binaries)
Irreducible seismic noise argues for space-based system at low frequencies - LISA
Three satellites forming interferometers with 5 x 106 km baselines (launch 2012?)
K. Riles - First Results from LIGO -2/24/04
9
Generation of Gravitational Waves
Strong indirect evidence for GW generation:
Taylor-Hulse Pulsar System (PSR1913+16)
Two neutron stars (one=pulsar)
in elliptical 8-hour orbit
Measured periastron advance
quadratic in time in agreement with
absolute GR prediction
Orbital decay due to energy loss
K. Riles - First Results from LIGO -2/24/04
10
Generation of Gravitational Waves
Can we detect this radiation directly?
NO - freq too low
Must wait ~300 My for characteristic “chirp”:
K. Riles - First Results from LIGO -2/24/04
11
Generation of Gravitational Waves
Coalescence rate estimates based on two methods: Use known NS/NS binaries in our galaxy (two!) A priori calculation from stellar and binary system evolution
Large uncertainties!
For initial LIGO design “seeing distance” (~20 Mpc):
Expect 1/(3000 y) to 1/(4 y)
Will need Advanced LIGO to ensure detection
K. Riles - First Results from LIGO -2/24/04
12
Generation of Gravitational Waves
Most promising periodic source: Rotating Neutron Stars (e.g., pulsar)
But axisymmetric object rotating about symmetry axis
Generates NO radiation
Radiation requires an asymmetry or perturbation:
Equatorial ellipticity (e.g., – mm-high “mountain”): h α εequat
Poloidal ellipticity (natural) + wobble angle: h α εpol x Θwobble
(precession due to different L and Ω axes)
Notation henceforth: ε = ( εequat or εpol x θwobble )
K. Riles - First Results from LIGO -2/24/04
13
Periodic Sources of GW
Serious technical difficulty: Doppler frequency shifts Frequency modulation from earth’s rotation (v/c ~ 10-6) Frequency modulation from earth’s orbital motion (v/c ~ 10-4)
Additional, related complications: Daily amplitude modulation of antenna pattern Spin-down of source Orbital motion of sources in binary systems
Modulations / drifts complicate analysis enormously: Simple Fourier transform inadequate Every sky direction requires different demodulation
All-sky survey at full sensitivity = Formidable challenge
K. Riles - First Results from LIGO -2/24/04
14
Periodic Sources of GW
But two substantial benefits from modulations: Reality of signal confirmed by need for corrections Corrections give precise direction of source
Difficult to detect neutron stars!
But search is nonetheless attractive & intriguing:
Unknown number of electromagnetically quiet, undiscovered
neutron stars in our galactic neighborhood
Realistic values for ε unknown
A nearby source could be buried in the data, waiting for just the
right algorithm to tease it into view
K. Riles - First Results from LIGO -2/24/04
15
Gravitational Wave Detection
Suspended Interferometers (IFO’s)
Suspended mirrors in “free-fall”
Broad-band response
(~50 Hz to few kHz)
Waveform information
(e.g., chirp reconstruction)
Michelson IFO is
“natural” GW detector
K. Riles - First Results from LIGO -2/24/04
16
Gravitational Wave Detection
Major Interferometers coming on line world-wide
LIGO (NSF-$300M)
Livingston, Louisiana & Hanford, Washington
2 x 4000-m
1 x 2000-m
Advanced
Commissioning
VIRGO
Near Pisa, Italy 1 x 3000-mEarly
Commissioning
GEO
Near Hannover, Germany 1 x 600-mAdvanced
Commissioning
TAMA
Tokyo, Japan 1 x 300-mAdvanced
Commissioning
K. Riles - First Results from LIGO -2/24/04
17
LIGO Interferometer Optical Scheme
end test mass
LASER/MC
6W
recyclingmirror
•Recycling mirror matches losses, enhances effective power by ~ 50x
150 W
20000 W(~0.5W)
Michelson interferometer
4 km Fabry-Perot cavity
With Fabry-Perot arm cavities
K. Riles - First Results from LIGO -2/24/04
18
“Locking” the Inteferometer
Sensing gravitational waves requires sustained resonance in the Fabry-Perot arms and in the recycling cavity
Need to maintain half-integer # of laser wavelengths between mirrors
Feedback control servo uses error signals from imposed RF sidebands
Four primary coupled degrees of freedom to control
Highly non-linear system with 5-6 orders of magnitude in light intensity
Also need to control mirror rotation (“pitch” & “yaw”)
Ten more DOF’s (but less coupled)
And need to stabilize laser (intensity & frequency), keep the beam pointed, damp out seismic noise, correct for tides, etc.,…
K. Riles - First Results from LIGO -2/24/04
19
Gravitational Wave Detection
Initial LIGO Design Sensitivity
Dominant noise sources:
•Seismic below 50 Hz
•Suspensions in 50-150 Hz
•Shot noise above 150 Hz
Best design sensitivity:
~3 x 10-23 Hz-1/2 @ 150 Hz
K. Riles - First Results from LIGO -2/24/04
20
LIGO Observatories
Livingston
Hanford
Observation of nearly simultaneous signals 3000 km apart rules out terrestrial artifacts
K. Riles - First Results from LIGO -2/24/04
21
LIGO Detector Facilities
Vacuum System
•Stainless-steel tubes
(1.24 m diameter, ~10-8 torr)
•Gate valves for optics isolation
•Protected by concrete enclosure
K. Riles - First Results from LIGO -2/24/04
22
LIGO Detector Facilities
LASER Infrared (1064 nm, 10-W) Nd-YAG laser from Lightwave (now commercial product!) Elaborate intensity & frequency stabilization system, including feedback from main
interferometer
Optics Fused silica (high-Q, low-absorption, 1 nm surface rms, 25-cm diameter) Suspended by single steel wire Actuation of alignment / position via magnets & coils
K. Riles - First Results from LIGO -2/24/04
23
LIGO Detector Facilities
Seismic Isolation Multi-stage (mass & springs) optical table support gives 106 suppression Pendulum suspension gives additional 1 / f 2 suppression above ~1 Hz
102
100
10-2
10-4
10-6
10-8
10-10
Horizontal
Vertical
10-6
K. Riles - First Results from LIGO -2/24/04
24
Livingston Problem -- Logging
Livingston Observatory located in pine forest popular with pulp wood cutters
Spiky noise (e.g. falling trees) in 1-3 Hz band creates dynamic range problem for arm cavity control
Solution:Retrofit with active feed-forward isolation system (using technology developed for Advanced LIGO)
Work started January 2004
K. Riles - First Results from LIGO -2/24/04
25
Correlation between seismic noise and lock livetime (4-day weekend)
K. Riles - First Results from LIGO -2/24/04
26
Sampling of Milestones
December 1999 First light in Hanford 2-km cavity & brief arm lock
April 2000 Engineering run “E1” (1 day, one 2-km arm)
October 2000 Hanford 2-km “First-Lock” (whole kit & caboodle)
March 2001 Engineering run “E3” (3 days, one Livingston arm)
January 2002 Eng. run “E7” (17 days, all IFO’s + GEO + ALLEGRO)
September 2002 Science run “S1” (17 days, all IFO’s + GEO + TAMA)
Results reported here
Feb. – April 2003 Science run “S2” (59 days, all IFO’s + TAMA)
October 2003 Eng. run “E10” (7 days, all IFO’s)
Nov 2003 – Jan 2004 Science run “S3” (66 days, all IFO’s + GEO + TAMA)
Just ended!
K. Riles - First Results from LIGO -2/24/04
27
The LIGO Scientific Collaboration (LSC)
LSC formed to
• Determine the scientific needs of the project and set R&D priorities
• Present the scientific case for the program
• Carry out the scientific and technical research program
• Carry out the data analysis and validate the scientific results
• Maximize scientific returns in the operations of LIGO Laboratory facilities
• Determine the relative distribution of observing and development time
• Establish the long term needs of the field & set priorities for improvements
Modeled in part on the successful high energy physics arrangement between national facilities and user group collaborations:
LIGO Laboratory = Caltech + MIT + Hanford + Livingston
K. Riles - First Results from LIGO -2/24/04
28
LSC Membership (~400 scientists)
University of Adelaide ACIGA
Australian National University ACIGA
Balearic Islands University
California State Dominquez Hills
Caltech LIGO
Caltech Experimental Gravitation CEGG
Caltech Theory CART
University of Cardiff GEO
Carleton College
Cornell University
Fermi National Laboratory
University of Florida @ Gainesville
Glasgow University GEO
NASA-Goddard Spaceflight Center
University of Hannover GEO
Hobart – Williams University
India-IUCAA
IAP Nizhny Novgorod
IUCCA India
Iowa State University
Joint Institute of Laboratory Astrophysics
Salish Kootenai College
LIGO Livingston Observatory (LLO)LIGO Hanford Observatory (LLO)
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
Syracuse University
University of Texas@Brownsville
Washington State University@ Pullman
University of Western Australia ACIGA
University of Wisconsin@Milwaukee
K. Riles - First Results from LIGO -2/24/04
29
Michigan LIGO Group MembersOld fogeys:
Dick Gustafson, Keith Riles
Graduate students:
Dave Chin, Vladimir Dergachev
Research assistant:
Jennifer Lindahl
Undergraduates:
Tim Bodiya, John Lucido, Jake Slutsky, Phil Szepietowski
Former undergraduates:
Jamie Rollins (now at MIT)
Justin Dombrowski (now at seminary)
Joseph Marsano (now at Harvard)
Michael La Marca (now at Arizona State)
K. Riles - First Results from LIGO -2/24/04
30
Michigan Group – Main Efforts
Initial work -- R&D at Caltech 40-Meter Prototype Interferometer
Demonstration of “recycling” with suspended interferometer
Last major R&D milestone for LIGO project
Apprenticeship for Gustafson and Riles
Detector Characterization (leadership, instrumentation, software)
Riles, Gustafson, Chin, Dergachev, Bodiya, Lucido
Commissioning & Noise Reduction
Gustafson (in residence at Hanford), Chin
Control System Development
Gustafson, Lindahl, Szepietowski, Riles
Search for Periodic Sources (rotating neutron stars)
Chin, Dergachev, Riles, Gustafson, Slutsky
K. Riles - First Results from LIGO -2/24/04
31
Data Analysis
Four “upper limits groups” organized: (to become “search groups”)
Inspiraling binary systems
Unmodelled bursts
Periodic sources (e.g. pulsars)
Stochastic background (e.g., big-bang remnant)
First steps:
Limits not yet astrophysically interesting
Understanding detector artifacts
Defining analysis algorithms and strategy (e.g., acceptable single-IFO signal rate prior to coincidence searching)
K. Riles - First Results from LIGO -2/24/04
32
S1 Instrumental Sensitivities
LIGO S1 Run----------“First
Upper Limit Run”
23 Aug–9 Sept 200217 daysAll IFOs in power recycling config LLO 4Km
LHO 2Km
LHO 4Km
GEO in S1 RUN----------
Ran simultaneouslyIn power recycling Lesser sensitivity
K. Riles - First Results from LIGO -2/24/04
33
Science Run S1 Data Analysis
As expected, S1 data much improved over earlier engineering run data in
• Sensitivity
• Gaussianity
• Stationarity
But significant residual artifacts remained and new problems emerged as the noise floor fell
Artifacts substantially complicated the data analysis
K. Riles - First Results from LIGO -2/24/04
34
S1 Data Quality(three hours of Livingston 4-km)
Histograms vs time of filtered GW channel
CLEAN DATA
RAGGED DATA
K. Riles - First Results from LIGO -2/24/04
35
S1 Data Quality – Inspiral Range (kpc)(“seeing distance” for inspiraling binary system)
Calibration not as stable as we wanted: (one day of S1 Hanford 4-km running)
K. Riles - First Results from LIGO -2/24/04
36
S1 Data Quality
Despite commissioning improvements, occasional artifacts appeared:
Hanford 4-km “heartbeat”
Tracked down to undamped “side motion” of one end mirror kicked up by Oregon earthquake
K. Riles - First Results from LIGO -2/24/04
37
Science Run S1 Data Analysis
Will summarize here results from searches for four types of gravitational wave sources:
• Inspiral coalescence of binary neutron star system
• Periodic source (pulsar)
• Stochastic gravitational wave background
• Bursts
K. Riles - First Results from LIGO -2/24/04
38
S1 Results
Search for binary inspiral coalescence of two neutron stars
Reporting limit on inspiral rate / milky-way equivalent galaxy (per year)
Search method relies upon matched filtering (frequency domain) of bank of template waveforms against the data
Searching over grid of neutron star mass pairs with M1 < M2 < 3 MSUN
Efficiency depends on distance to binary system
Define “inspiral candle” range to be distance at which binary system of 2 × 1.4MSUN neutron stars can be detected with SNR=8 in optimal orientation
K. Riles - First Results from LIGO -2/24/04
39
S1 RangesL1: 110 kpc < D < 210 kpc
H1: 40 kpc < D < 75 kpc
H2: 38 kpc < D < 70 kpc
Visible: Milky Way
LMC, SMC
K. Riles - First Results from LIGO -2/24/04
40
Inspiral Results: [gr-qc/0308069 – submitted to PRD]
Use all candidates from Hanford and Livingston: 236 hours Cannot accurately assess background (be conservative, assume zero) Use maximum signal-to-noise ratio statistic to establish the rate limit. Monte Carlo simulation efficiency = 0.51 90% confidence limit = 2.3 / (efficiency * time) Express the rate as a rate per Milky-Way Equivalent Galaxies (MWEG)
R < 2.3 / (0.50 x 236 hr) = 1.7 x 102 / yr / (MWEG)
Previous observational limits Japanese TAMA R < 30,000 / yr / MWEG Caltech 40m R < 4,000 / yr / MWEG
Theoretical prediction R < 2 x 10-5 / yr / MWEG
K. Riles - First Results from LIGO -2/24/04
41
Loudest Surviving Event Candidate
Not NS/NS inspiral event 1 Sep 2002, 00:38:33 UTC S/N = 15.9, 2/dof = 2.2 (m1,m2) = (1.3, 1.1) Msun
SNR vs time:
χ2 vs time:
Study of auxiliary channels reveals:
Photodiode Saturation!
K. Riles - First Results from LIGO -2/24/04
42
S1 Results (cont.)
Search for periodic sources of gravitational radiation
Chose to focus on single (fastest) pulsar:
J1939+2134 fGW = 1.28 kHz
Two independent searches carried out:
Time Domain (heterodyne with modulation correction)
Frequency Domain (FFT stitching with correction)
Doppler modulations and pulsar spin-down explicitly taken into account in these coherent targeted analyses
K. Riles - First Results from LIGO -2/24/04
43
Graphic by R. Dupuis, Glasgow
Detectable amplitudes with a 1% false alarm rate and 10% false dismissal rate by the IFOs during S1 (colored curves) and at design sensitivities (black curves)
Upper limits on <ho> from spin-down measurements of known radio pulsars (filled circles)
<ho>= 11.4 [Sh(fo)/T]1/2
Expectations for pulsar strain amplitude sensitivity
S1: NO DETECTIONEXPECTED
PSR J1939+2134P = 0.00155781 sfGW = 1283.86 Hz
P = 1.0511 10-19 s/sD = 3.6 kpc
.
Crab pulsar
K. Riles - First Results from LIGO -2/24/04
44
Pulsar Results: [ gr-qc/0308050 –to appear in PRD]
No evidence of continuous wave emission from PSR J1939+2134 – As expected
Summary of 95% upper limits on h:
• ho < 1.4 x 10-22 constrains ellipticity < 3 x 10-4 (M=1.4Msun, r=10km, R=3.6kpc)
• Previous best result for PSR J1939+2134: ho < 10-20 (Glasgow, Hough et al., 1983)
IFO Frequentist FDS Bayesian TDS
GEO (1.9 0.1) x 10-21 (2.2 0.1) x 10-21
LLO (2.7 0.3) x 10-22 (1.4 0.1) x 10-22
LHO-2K (5.4 0.6) x 10-22 (3.3 0.3) x 10-22
LHO-4K (4.0 0.5) x 10-22 (2.4 0.2) x 10-22
K. Riles - First Results from LIGO -2/24/04
45
S1 Results (cont.)
Search for stochastic background of gravitational waves
Sources: early universe, many weak unresolved sources emitting gravitational waves independently Random radiation described by its spectrum (isotropic, unpolarized, stationary and Gaussian)
Analysis goals: constrain contribution of stochastic radiation’s energy GW to the total energy required to close the universe critical :
0
(1/ ) ( ) GWGW
critical
f f df
K. Riles - First Results from LIGO -2/24/04
46
Methods for the Stochastic Search
Optimally filtered cross-correlation of detector pairs: L1-H1, L1-H2 and H1-H2.
o
• Detector separation and orientation reduce correlations at high frequencies (GW > 2xBaseLine): overlap reduction function» H1-H2 best suited
» L1-H1(H2) significant <50Hz
• Achievable sensitivities to by detector pairs in S1 [assumes (f) = 0 ]
K. Riles - First Results from LIGO -2/24/04
47
Results of Stochastic Search [ gr-qc/0312088 – submitted to PRD]
Non-negligible LHO 4km-2km (H1-H2) cross-correlation due to common
acoustic coupling (now much improved!)
51 hrs
64 hrs
Tobs
GW (40Hz - 314 Hz) < 23 5
GW (40Hz - 314 Hz) < 55 11
90% CL Upper Limit
LHO 2km-LLO 4km
LHO 4km-LLO 4km
Interferometer Pair
Previous best upper limits:
Measured: Garching-Glasgow interferometers :
Measured: EXPLORER-NAUTILUS (cryogenic bars):
GW ( f ) 3105
GW (907Hz) 60
K. Riles - First Results from LIGO -2/24/04
48
S1 Results (cont.)
Search for gravitational wave bursts
Sources: Known and unknown phenomena emitting short transients of gravitational radiation of unknown waveform (e.g., supernovae, black hole mergers).
Analysis goals: Broad frequency band search to (a) establish a bound on their rate at the instruments, (b) interpret bound in terms of a source and population model on a rate vs. strength exclusion plot.
Search method: Time-Frequency domain algorithm identifies regions in the time-frequency plane with excess power (threshold on pixel power and cluster size – “tfcluster”).
K. Riles - First Results from LIGO -2/24/04
49
Bursts Search Pipeline
basic assumption: multi-interferometer response consistent with a plane wave-front incident on network of detectors.
design the capability to veto data epochs and events based on quality criteria and auxiliary channels.
essential: use temporal coincidence of the 3 interferometer’s ‘best candidates’
correlate frequency features of candidates (time-frequency domain analysis).
Search code generated events
Epoch veto’ed
Can be veto’ed by auxiliary channels
K. Riles - First Results from LIGO -2/24/04
50
Upper Limit on Rate of Bursts
End result of analysis pipeline: number of triple coincidence events. Use time-shift experiments to establish number of background events. Use Feldman-Cousins to set 90% confidence upper limits on rate of
foreground events:
< 1.6 events/day
Background estimation for TFCLUSTERS in S1
Zero-lag measurement
Poisson fit of timeshifted coincidencesbetween the LIGO sites
K. Riles - First Results from LIGO -2/24/04
51
90% CL Rate limit vs. Strength Plots for a Burst Model
Optimally oriented(per IFO)
Average over direction,Polarization (per IFO)
Burst model:
Sine-Gaussians with varying central frequencies
Burst model:
1ms, 2.5 ms Gaussian impulses
Determine detection efficiency of the end-to-end analysis pipeline via signal injection of various morphologies.
Assume a population of such sources uniformly distributed on a sphere around us: establish upper limit on rate of bursts as a function of their strength.
K. Riles - First Results from LIGO -2/24/04
52
Burst Search Results and the Future [ gr-qc/0312056 –to appear in PRD]
Search and raw results sensitive to a wide variety of waveform morphologies and broad frequency features (as long as signal has significant strain amplitude in LIGO’s frequency band).
90% CL upper limit of 1.6 events/day leads to limits on characteristic strain strength ~ 10-19 -- 10-17 / √Hz.
In the near future: Use multiple-interferometer information on amplitude of putative
signal and correlation statistic of their raw time-series. Improve time-resolution of event trigger generators. Pursue rigorously an externally triggered (by GRB’s, neutrinos)
search for bursts (excercised during S1).
K. Riles - First Results from LIGO -2/24/04
53
Looking Ahead
S1 analysis was a good exercise for operations and data analysis
Learning how to confront instrumental artifacts in astrophysical searches (no more Gaussian noise modelling!)
Excellent preparation for more sensitive future Science Runs
Meanwhile, IFO’s ever improving with further commissioning …
K. Riles - First Results from LIGO -2/24/04
54
Looking Ahead
May 01
Jan 03
Livingston 4-km IFO sensitivity history until S2:
Initial LIGO Design
K. Riles - First Results from LIGO -2/24/04
55
Looking Ahead
Initial LIGO Design
S11st Science Runend Sept. 2002
17 daysS22nd Science Runend Apr. 2003
59 days
S33rd Science Runbegin Nov. 2003
70 days
K. Riles - First Results from LIGO -2/24/04
56
Looking Ahead
The three LIGO interferometers are part of a forming global network.
Multiple signal detections will increase detection confidence and provide better precision on source locations and wave polarizations
LIGO GEO Virgo
TAMA
AIGO (proposed)
K. Riles - First Results from LIGO -2/24/04
57
Looking Way Ahead
Despite their immense technical challenges, the initial LIGO IFO’s were designed conservatively, based on “tabletop” prototypes, but with expected sensitivity gain of ~1000.
Given the expected low rate of detectable GW events, it was always planned that in engineering, building and commissioning initial LIGO, one would learn how reliably to build Advanced LIGO with another factor of ~10 improved sensitivity.
Because LIGO measures GW amplitude, an increase in sensitivity by 10 gives an increase in sampling volume, i.e, rate by ~1000
K. Riles - First Results from LIGO -2/24/04
58
Advanced LIGO
Detector Improvements:
Improved seismic isolation: Passive Active
Lowers seismic “wall” to ~12 Hz
New suspensions: Single Quadruple pendulum
Lower suspensions thermal noise in bandwidth
Increased test mass: 10 kg 30 kg
Compensates increased radiation pressure noise
New test mass material: Fused silica Sapphire
Lower internal thermal noise in bandwidth
Increased laser power: 10 W 180 W
Improved shot noise (high freq)
K. Riles - First Results from LIGO -2/24/04
59
Advanced LIGO
Sampling of source strengths vis a vis Initial LIGO and Advanced LIGO
Lower hrms and wider bandwidth both important
“Signal recycling” offers potential for tuning shape of noise curve to improve sensitivity in target band (e.g., known pulsar range)
K. Riles - First Results from LIGO -2/24/04
60
Advanced LIGO
Ambitious upgrade program:
• MRE proposal submitted to NSF in January
• Technical review went very well, but more layers to go
• Hope to begin detector upgrades in 2007
Begin observing in 2008
First 2-3 hours of Advanced LIGO is equivalent
to a “Snowmass year” of Initial LIGO
K. Riles - First Results from LIGO -2/24/04
61
Summary
Initial LIGO commissioning well underway
Much instrumental noise to beat down, but no show-stoppers have appeared
Engineering runs giving way to sporadic science runs (with astrophysical measurements as primary purpose) interspersed with ongoing commissioning
Confronting dirty-data analysis First astrophysics results
Looking ahead to several years of high-duty-cycle data taking
Looking farther ahead to major detector upgrade with more than 1000-fold increase in event rate
Direct GW detection only a matter of time
Exciting years to come!
Recommended