direct searches for stochastic gravitational waves with ligo: status and prospects

LIGO-G050247-01-E

Direct Searches for Stochastic Gravitational Waves with LIGO: status and prospects

Direct Searches for Stochastic Gravitational Waves with LIGO: status and prospects

Albert LazzariniCalifornia Institute of Technology

On behalf of the LIGO Scientific Collaboration

The 11th International Symposium onParticles, Strings and Cosmology

30 May 2005Gyeongju, Korea

Albert LazzariniCalifornia Institute of Technology

On behalf of the LIGO Scientific Collaboration

The 11th International Symposium onParticles, Strings and Cosmology

30 May 2005Gyeongju, Korea

Black Holes courtesy of NCSA

LIGO Laboratory at CaltechLIGO-G050247-01-E

Outline of PresentationOutline of Presentation Stochastic gravitational waves

Characterization of strain Sources

LIGO Concept Principle of operation Sites, facilities Sensitivity

Recent observational results Prospects

Stochastic gravitational waves Characterization of strain Sources

LIGO Concept Principle of operation Sites, facilities Sensitivity

Recent observational results Prospects


Stochastic gravitational wave backgroundStochastic gravitational wave backgroundStochastic gravitational wave backgroundStochastic gravitational wave background

• Detect by cross-correlating interferometer outputs in pairs• US-LIGO : Hanford, Livingston • Europe: GEO600, Virgo• Japan: TAMA

• Good sensitivity requires:• GW > 2D (detector baseline)• f < 40 Hz for LIGO pair over 3000 km baseline

• Initial LIGO limiting sensitivity (1 year search): <10-6

Analog from cosmic microwave background -- WMAP 2003

GWs are the able to probe the very early universe GWs are the able to probe the very early universe

The integral of [1/f•GW(f)] over all frequencies corresponds to the fractional

energy density in gravitational waves in the Universe


Cosmological Gravitational WavesCosmological Gravitational Waves

Terrestrial


Characterization of a Stochastic Gravitational Wave BackgroundCharacterization of a Stochastic Gravitational Wave Background

Allen & Romano, Phys.Rev. D59 (1999)

GW energy density given by time derivative of strain

Assuming SGWB is isotropic, stationary and Gaussian, the strength is fully specified by the energy density in GWs

f) in terms of a measurable strain power spectrum, Sgw(f):

Strain amplitude scale:


Stochastic signals fromcosmological processesStochastic signals fromcosmological processes

Inflation -- flat spectrumKolb & Turner, The Early Universe

Phase transitions -- peaked at phase transition energy scale

Kamionkowski, Kosowski & Turner, Phys.Rev. D49 (1994)Apreda et al., Nucl.Phys. B631 (2002)

Cosmic strings -- gradually decreasing spectrumDamour & Vilenkin , Phys.Rev. D71 (2005)

Pre big-bang cosmologyBuonanno, Maggiore & Ungarellli , Phys.Rev. D55 (1997)


Incoherent superposition of many signals from various signal classes Coalescing binaries Supernovae Pulsars Low Mass X-Ray Binaries (LMXBs) Newly born neutrons stars

Normal modes - R modes Binary black holes

Gaussian -> non-Gaussian (“popcorn” noise) depending on rates

Drasco & Flannigan, Phys.Rev. D67 (2003),

Spectra follow from characteristics of individual sources

Maggiore, Phys.Rept. 331 (2000)

Incoherent superposition of many signals from various signal classes Coalescing binaries Supernovae Pulsars Low Mass X-Ray Binaries (LMXBs) Newly born neutrons stars

Normal modes - R modes Binary black holes

Gaussian -> non-Gaussian (“popcorn” noise) depending on rates

Drasco & Flannigan, Phys.Rev. D67 (2003),

Spectra follow from characteristics of individual sources

Maggiore, Phys.Rept. 331 (2000)

Stochastic signals from astrophysical processesStochastic signals from

astrophysical processes


n & Koranda, PRD 50 (1994)

Kolb & Turner, The Early Universe (1990)

The Cosmological Gravitational Wave “Landscape”


Armstrong et al., ApJ 599 (2003)

Lommen, astro-ph/0208572

Range of

Interferometers (Ground & Space-

Based


The LIGO Laboratory SitesThe LIGO Laboratory Sites

Caltech

MIT

3002 km

(L/c = 10 ms)

Livingston, LA

Hanford, WA

Interferometers are aligned along the great circle connecting the sites


The LIGO ObservatoriesThe LIGO ObservatoriesThe LIGO ObservatoriesThe LIGO Observatories

Livingston ObservatoryLouisianaOne interferometer (4km)

GEODETIC DATA (WGS84)h: -6.574 m X arm: S72.2836°W: N30°33’46.419531” Y arm: S17.7164°E: W90°46’27.265294”

Hanford, WA ->

Hanford ObservatoryWashingtonTwo interferometers(4 km and 2 km arms)

GEODETIC DATA (WGS84) h: 142.555 m X arm: N35.9993°W: N46°27’18.527841” Y arm: S54.0007°W: W119°24’27.565681”

<- Livingston, LA


Detector conceptDetector concept The concept is to compare the time it takes light to travel in two

orthogonal directions transverse to the gravitational waves. The gravitational wave causes the time difference to vary by

stretching one arm and compressing the other. The interference pattern is measured (or the fringe is split) to

one part in 1010, in order to obtain the required sensitivity.

The concept is to compare the time it takes light to travel in two orthogonal directions transverse to the gravitational waves.

The gravitational wave causes the time difference to vary by stretching one arm and compressing the other.

The interference pattern is measured (or the fringe is split) to one part in 1010, in order to obtain the required sensitivity.

h = L/L => / = 2 Nb hL/

QuickTime™ and aAnimation decompressor

are needed to see this picture.Light makesNb bounces


LIGO First Generation Detector

Limiting noise floor

LIGO First Generation Detector

Limiting noise floor Interferometer sensitivity is limited by three fundamental noise sources

seismic noise at the lowest frequencies thermal noise (Brownian motion of mirror materials, suspensions) at intermediate frequencies shot noise at high frequencies

Many other noise sources lie beneath and must be controlled as the instrument is improved


factor 2X of design goal throughout LIGO band

The LIGO is Approaching its Design Sensitivity

The LIGO is Approaching its Design Sensitivity


Detection strategyDetection strategy

Cross-correlation statistic:

Optimal filter (assume gw(f) = const):

Make many (N~ 104) repeated short (T = 60s) measurements to track instrumental variations:

Spectrum:


(f)

(f) - Overlap reduction factor(f) - Overlap reduction factor


S2 H1-L1 results using previously outlined methodS2 H1-L1 results using previously outlined method

Distribution of over S2 run

i i

Scatter plot of normalized residuals vs.

i

i

2

i

22896


S3 Expected Sensitivity: H1-L1

S3 Expected Sensitivity: H1-L1Estimated error of measurement (+3 plotted for the H1-L1 pair as a

function of run time.

Preliminary


H-L H1-H2 Freq range Observation Time

S1 (upper limit) PRD 69, 122004,

2004

< 23 +/- 4.6(H2-L1)

see instrumental noise 64-265 Hz 64 hours(08/23/02 – 09/09/02)

S2 (upper limit) Preliminary

< 0.018 +0.007- 0.003(H1-L1)

see instrumental noise 50-300 Hz 387 hours(02/14/03 – 04/14/03)

S3 (sensitivity) Expected based on

power spectra

~5 x 10-4

(H1-L1)potentially ~10x lower

than S3 H1-L150-300 Hz ~240 hours

(10/31/03 – 01/09/04)

Design sensitivities LIGO I ~1x 10-6 ~1.5x 10-7 30-300 Hz 1 year

LIGO Advanced nominal tuning low-freq tuning

~1.5x 10-9

~3.5x 10-10

~3x 10-10

~2.5x 10-10

10-100 Hz10-50 Hz

1 year1 year

Current and expected results on gw h1002Current and expected results on gw h1002


Frequency range for GW Astronomy

Frequency range for GW Astronomy

Dynamic range of Gravitational

Waves

Terrestrial and space detectors complementary probes

Provide ~8 orders of magnitude coverage

Dynamic range of Gravitational

Waves

Terrestrial and space detectors complementary probes

Provide ~8 orders of magnitude coverage

Space Terrestrial

Audio band


Initial and Advanced LIGOInitial and Advanced LIGO


Operated as a phased array:- Enhance detection confidence- Localize sources-- Decompose the polarization of gravitational waves-- Precursor triggers from low frequency

LISA

Growing International Network of GW InterferometersGrowing International Network of GW InterferometersGrowing International Network of GW InterferometersGrowing International Network of GW Interferometers

VIRGO: 3km2005 - 2006

AIGO: (?)kmProposed

LIGO-LHO: 2km, 4kmOn-line

LIGO-LLO: 4kmOn-line

GEO: 0.6kmOn-line

TAMA: 0.3kmOn-line


SummarySummary The current best published IFO-IFO upper-limit is from S1:

h2 < 23+/-4.6 S2 result: 0.018 (+0.007- 0.003) PRELIMINARY The S3 data analysis is in progress. Expect: < few x 10-4

H1-H2 is the most sensitive pair, but it also suffers from cross-correlated instrumental noise.

Also working on: Set limits for gw(f) ~ n(f/f0)n

Targeted searches (astrophysical foregrounds, spatially resolved map)

Expected sensitivities with one year of data from LLO-LHO: Initial LIGO h2 < 2x10-6

Advanced LIGO h2 < 7x10-10

The current best published IFO-IFO upper-limit is from S1: h2 < 23+/-4.6 S2 result: 0.018 (+0.007- 0.003) PRELIMINARY The S3 data analysis is in progress. Expect: < few x 10-4

H1-H2 is the most sensitive pair, but it also suffers from cross-correlated instrumental noise.

Also working on: Set limits for gw(f) ~ n(f/f0)n

Targeted searches (astrophysical foregrounds, spatially resolved map)

Expected sensitivities with one year of data from LLO-LHO: Initial LIGO h2 < 2x10-6

Advanced LIGO h2 < 7x10-10


FINISFINIS


What is known about the stochastic gravitational wave background?

What is known about the stochastic gravitational wave background?

2

Allen & Koranda, PhysRevD

Lommen, astro-ph/0208572

Kolb & Turner, TheEarlyUniverseAddisonWesley1990

direct searches for stochastic gravitational waves with ligo: status and prospects

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